mempool: snapshot

2026-06-08 14:11:56 -07:00 · 2025-12-13 16:26:29 +01:00
parent 9c8b9b1a3b
commit c59ac62e45
22 changed files with 1808 additions and 582 deletions
@@ -737,12 +737,14 @@ name = "brk_monitor"
 version = "0.0.111"
 dependencies = [
 "brk_error",
+ "brk_logger",
 "brk_rpc",
 "brk_types",
 "derive_deref",
 "log",
 "parking_lot",
 "rustc-hash",
+ "smallvec",
 ]

 [[package]]
@@ -74,6 +74,7 @@ serde = "1.0.228"
 serde_bytes = "0.11.19"
 serde_derive = "1.0.228"
 serde_json = { version = "1.0.145", features = ["float_roundtrip"] }
+smallvec = "1.15.1"
 tokio = { version = "1.48.0", features = ["rt-multi-thread"] }
 vecdb = { path = "../anydb/crates/vecdb", features = ["derive", "serde_json", "pco"] }
 # vecdb = { git = "https://github.com/anydb-rs/anydb", features = ["derive", "serde_json", "pco"] }
@@ -28,7 +28,7 @@ pco = "0.4.7"
 rayon = { workspace = true }
 rustc-hash = { workspace = true }
 serde = { workspace = true }
-smallvec = "1.15.1"
+smallvec = { workspace = true }
 vecdb = { workspace = true }

 [dev-dependencies]
@@ -94,11 +94,11 @@ fn write(
    dash: impl Display,
    args: impl Display,
 ) -> Result<(), std::io::Error> {
-    // writeln!(buf, "{date_time} {dash} {level} {args}")
+    writeln!(buf, "{date_time} {dash} {level} {args}")
    // Don't remove, used to know the target of unwanted logs
-    writeln!(
-        buf,
-        "{} {} {} {}  {}",
-        date_time, _target, level, dash, args
-    )
+    // writeln!(
+    //     buf,
+    //     "{} {} {} {}  {}",
+    //     date_time, _target, level, dash, args
+    // )
 }
@@ -16,3 +16,7 @@ derive_deref = { workspace = true }
 log = { workspace = true }
 parking_lot = { workspace = true }
 rustc-hash = { workspace = true }
+smallvec = { workspace = true }
+
+[dev-dependencies]
+brk_logger = { workspace = true }
@@ -0,0 +1,455 @@
+# Mempool Projected Blocks - Design Document
+
+## Goal
+
+Efficiently maintain projected blocks for fee estimation without rebuilding everything on each mempool change.
+
+## Core Idea
+
+Instead of rebuilding all projected blocks on every insert/remove:
+1. Insert new tx/package into the correct block (binary search by fee rate)
+2. Cascade overflow: if block > 1MB, move lowest fee rate item to next block
+3. On remove: cascade up to fill the gap
+
+## Data Structures
+
+### MempoolPackage
+
+```rust
+enum MempoolPackage {
+    /// Tx with no unconfirmed parents - can be mined independently
+    Independent(MempoolEntry),
+
+    /// Tx(s) bundled for CPFP - ancestors + paying descendant
+    Bundle {
+        /// The descendant tx that "pays for" the ancestors
+        child: Txid,
+        /// All txs in topological order (ancestors first, child last)
+        entries: Vec<MempoolEntry>,
+        /// Sum of all fees
+        total_fee: Sats,
+        /// Sum of all vsizes
+        total_vsize: VSize,
+    },
+
+    /// Tx waiting for unconfirmed parent(s) that are in a different Bundle
+    /// Not placed in projected blocks until dependencies clear
+    Pending {
+        entry: MempoolEntry,
+        /// Parent txids this tx is waiting for
+        waiting_for: FxHashSet<Txid>,
+    },
+}
+```
+
+### ProjectedBlock
+
+```rust
+struct ProjectedBlock {
+    /// Packages sorted by fee rate (highest first)
+    packages: Vec<MempoolPackage>,
+    /// Current total vsize
+    total_vsize: VSize,
+    /// Running fee total
+    total_fee: Sats,
+}
+```
+
+## Insert Algorithm
+
+### Case 1: No unconfirmed parents
+```
+tx A (10 sat/vB), no unconfirmed inputs
+```
+→ Create `Independent(A)`
+→ Binary search blocks by fee rate, insert, cascade overflow
+
+### Case 2: Has unconfirmed parent(s), CPFP beneficial
+```
+tx P (2 sat/vB) → tx C (50 sat/vB)
+Package rate = (P.fee + C.fee) / (P.vsize + C.vsize) = 26 sat/vB
+26 > max(2, 50)? No, 26 < 50
+```
+Wait, need to reconsider: CPFP is beneficial when child NEEDS parent to be mined.
+The package rate matters for when C will be mined (C can't be mined without P).
+
+Actually: C's effective rate = package rate, always. Because C cannot be mined without P.
+
+So: Create `Bundle { child: C, entries: [P, C], rate: 26 }`
+
+If P was already `Independent(P)` in a block:
+1. Remove P from its block
+2. Create Bundle
+3. Insert Bundle at rate 26 sat/vB
+
+### Case 3: Chain of unconfirmed txs
+```
+tx A (2 sat/vB) → tx B (3 sat/vB) → tx C (100 sat/vB)
+```
+C's package = A + B + C
+→ `Bundle { child: C, entries: [A, B, C] }`
+
+If A and B were already placed:
+1. Remove A, B from their positions
+2. Create Bundle with all three
+3. Insert at package fee rate
+
+### Case 4: Diamond dependency
+```
+    tx A (5 sat/vB)
+   ↙            ↘
+tx B (2)       tx C (2)
+   ↘            ↙
+    tx D (100 sat/vB)
+```
+D's ancestors = {A, B, C}
+→ `Bundle { child: D, entries: [A, B, C, D] }` (topological order)
+
+### Case 5: Multiple children competing for same parent
+```
+tx P (2 sat/vB)
+    ├→ tx C1 (50 sat/vB)  → package rate 26 sat/vB
+    └→ tx C2 (100 sat/vB) → package rate 51 sat/vB
+```
+P can only be in ONE package (can only be mined once).
+
+Choose the highest package fee rate: P + C2 at 51 sat/vB
+→ `Bundle { child: C2, entries: [P, C2] }`
+
+What happens to C1?
+- C1 cannot be mined until P is mined
+- C1 becomes `Pending { entry: C1, waiting_for: {P} }`
+- C1 is NOT in projected blocks
+
+When Bundle(P, C2) is mined:
+- P leaves mempool
+- C1's waiting_for becomes empty
+- C1 converts to `Independent(C1)` at 50 sat/vB
+- C1 gets inserted into projected blocks
+
+### Case 6: New tx improves existing Bundle
+```
+Existing: Bundle { child: C, entries: [P, C], rate: 26 }
+New tx D spends C's output, D has very high fee
+New package rate (P + C + D) = 40 sat/vB
+```
+Since 40 > 26:
+1. Remove old Bundle from its block
+2. Create new `Bundle { child: D, entries: [P, C, D] }`
+3. Insert at new rate
+
+### Case 7: New tx doesn't improve, becomes Pending
+```
+Existing: Bundle { child: C, entries: [P, C], rate: 26 }
+New tx D spends C's output, D has low fee
+New package rate (P + C + D) = 20 sat/vB
+```
+Since 20 < 26, D doesn't help:
+→ `Pending { entry: D, waiting_for: {C} }`
+
+When Bundle(P, C) is mined:
+→ D converts to `Independent(D)`
+
+## Remove Algorithm
+
+### Case 1: Remove an `Independent`
+```
+Remove Independent(A) from block 3
+```
+1. Remove A from block 3
+2. Block 3 now has space
+3. Pull highest fee rate package from block 4 into block 3
+4. Cascade: pull from block 5 to block 4, etc.
+5. Stop when a block has no underflow or no more blocks
+
+### Case 2: Remove the "child" (paying tx) of a Bundle
+```
+Bundle { child: C, entries: [P, C] } in block 2
+C gets dropped/RBF'd (NOT confirmed - if confirmed, P would be too)
+```
+1. Remove Bundle from block 2
+2. P has no more CPFP boost
+3. P becomes `Independent(P)` at its own rate (2 sat/vB)
+4. Insert P into appropriate block (probably much later)
+5. Cascade to fill block 2's gap
+
+### Case 3: Remove an ancestor from a Bundle (confirmation)
+```
+Bundle { child: C, entries: [P, C], rate: 26 } in block 2
+P gets confirmed (separate from C? unusual but possible in reorg)
+```
+1. Remove Bundle from block 2
+2. C no longer needs P
+3. C becomes `Independent(C)` at 50 sat/vB
+4. Insert C into earlier block (higher rate now)
+5. Cascade as needed
+
+### Case 4: Remove tx that has Pending descendants
+```
+Independent(P) in block 5
+Pending { entry: C, waiting_for: {P} }
+P gets confirmed
+```
+1. Remove P from block 5
+2. Find all Pending txs waiting for P
+3. For each: remove P from waiting_for
+4. If waiting_for is empty: convert to Independent, insert into blocks
+5. Cascade to fill block 5's gap
+
+### Case 5: Remove middle of a chain (tx dropped/invalid)
+```
+Bundle { child: D, entries: [A, B, C, D] }
+B gets dropped (double-spend, RBF, etc.)
+```
+B invalid means C and D are invalid too (missing input):
+1. Remove entire Bundle
+2. A becomes `Independent(A)` if still valid
+3. C, D removed from mempool entirely
+
+### Case 6: RBF replacement
+```
+Independent(A) in block 3
+New tx A' replaces A (same inputs, higher fee)
+```
+1. Remove A (and any descendants - they're now invalid)
+2. Insert A' as new Independent or Bundle
+
+## Pending → Active Transitions
+
+When a tx is removed (confirmed), check all `Pending` entries:
+
+```rust
+fn on_tx_removed(&mut self, txid: Txid) {
+    let pending_to_update: Vec<_> = self.pending
+        .iter()
+        .filter(|(_, p)| p.waiting_for.contains(&txid))
+        .map(|(id, _)| *id)
+        .collect();
+
+    for pending_txid in pending_to_update {
+        let pending = self.pending.get_mut(&pending_txid).unwrap();
+        pending.waiting_for.remove(&txid);
+
+        if pending.waiting_for.is_empty() {
+            // Convert to Independent and insert
+            let entry = self.pending.remove(&pending_txid).unwrap();
+            self.insert_independent(entry.entry);
+        }
+    }
+}
+```
+
+## Cascade Algorithm
+
+### Cascade Down (after insert causes overflow)
+
+```rust
+fn cascade_down(&mut self, starting_block: usize) {
+    let mut block_idx = starting_block;
+
+    while block_idx < self.blocks.len() {
+        let block = &mut self.blocks[block_idx];
+
+        if block.total_vsize <= BLOCK_VSIZE_TARGET {
+            break; // No overflow
+        }
+
+        // Pop lowest fee rate package
+        let overflow = block.packages.pop().unwrap();
+        block.total_vsize -= overflow.vsize();
+        block.total_fee -= overflow.fee();
+
+        // Push to next block
+        if block_idx + 1 >= self.blocks.len() {
+            self.blocks.push(ProjectedBlock::new());
+        }
+
+        let next_block = &mut self.blocks[block_idx + 1];
+        // Insert at beginning (it's the highest fee rate in this block)
+        next_block.packages.insert(0, overflow);
+        next_block.total_vsize += overflow.vsize();
+        next_block.total_fee += overflow.fee();
+
+        block_idx += 1;
+    }
+}
+```
+
+### Cascade Up (after remove causes underflow)
+
+```rust
+fn cascade_up(&mut self, starting_block: usize) {
+    let mut block_idx = starting_block;
+
+    while block_idx < self.blocks.len() {
+        let current_vsize = self.blocks[block_idx].total_vsize;
+
+        if current_vsize >= BLOCK_VSIZE_TARGET {
+            break; // Block is full enough
+        }
+
+        if block_idx + 1 >= self.blocks.len() {
+            break; // No more blocks to pull from
+        }
+
+        let next_block = &mut self.blocks[block_idx + 1];
+        if next_block.packages.is_empty() {
+            // Remove empty block
+            self.blocks.remove(block_idx + 1);
+            break;
+        }
+
+        // Pull highest fee rate package from next block
+        let pulled = next_block.packages.remove(0);
+        next_block.total_vsize -= pulled.vsize();
+        next_block.total_fee -= pulled.fee();
+
+        // Add to current block
+        let current_block = &mut self.blocks[block_idx];
+        current_block.packages.push(pulled);
+        current_block.total_vsize += pulled.vsize();
+        current_block.total_fee += pulled.fee();
+
+        block_idx += 1;
+    }
+
+    // Clean up empty trailing blocks
+    while self.blocks.last().map(|b| b.packages.is_empty()).unwrap_or(false) {
+        self.blocks.pop();
+    }
+}
+```
+
+## Data Structure for Efficient Operations
+
+Need to track:
+1. `txid → MempoolPackage` - which package contains a tx
+2. `txid → block_index` - which block a tx/package is in
+3. `txid → Vec<Txid>` - descendants waiting for this tx (Pending)
+4. Per-block: sorted packages by fee rate
+
+```rust
+struct MempoolState {
+    /// All packages (Independent, Bundle, or Pending)
+    packages: FxHashMap<Txid, MempoolPackage>,
+
+    /// For Bundle: maps each txid in bundle to the child txid (package key)
+    tx_to_package: FxHashMap<Txid, Txid>,
+
+    /// Maps package key (txid) to block index, None if Pending
+    package_to_block: FxHashMap<Txid, Option<usize>>,
+
+    /// Maps txid to list of Pending txids waiting for it
+    waiting_on: FxHashMap<Txid, FxHashSet<Txid>>,
+
+    /// The projected blocks
+    blocks: Vec<ProjectedBlock>,
+}
+```
+
+## Open Questions
+
+1. **Block fullness threshold**: Should we cascade when exactly at 1MB, or allow slight overflow?
+
+2. **Minimum fee rate**: Packages below minimum relay fee should be excluded?
+
+3. **Maximum ancestors**: Bitcoin Core limits ancestor count (25). Should we?
+
+4. **Memory bounds**: For huge mempools, should we limit projected blocks count?
+
+## mempool.space Implementation Analysis
+
+Source: [mempool/mempool rust/gbt/src](https://github.com/mempool/mempool/tree/master/rust/gbt/src)
+
+### Key Files
+- `gbt.rs` - Main block building algorithm
+- `audit_transaction.rs` - Transaction wrapper with ancestor tracking
+- `thread_transaction.rs` - Lightweight tx representation
+
+### Their Approach
+
+**Not incremental!** They rebuild from scratch but optimize heavily:
+
+1. **Use numeric UIDs** instead of 32-byte txids - massive memory/hash savings
+2. **Ancestor score** = (fee + ancestor_fees) / (weight + ancestor_weights)
+3. **Two-source selection**:
+   - `mempool_stack`: Original sorted order
+   - `modified` priority queue: Txs whose scores changed due to parent selection
+4. **Greedy selection loop**:
+   - Pick highest ancestor score from either source
+   - Include all ancestors first
+   - Update all descendants' scores (via `update_descendants()`)
+   - Move affected descendants to `modified` queue
+
+### Why They Don't Do Incremental
+
+The `update_descendants()` cascade is the key insight: when you select a tx, ALL its descendants need score recalculation because their ancestor set changed. This cascade can touch a huge portion of the mempool.
+
+Their solution: rebuild fast rather than update incrementally.
+- Use u32 UIDs (4 bytes vs 32 bytes)
+- Pre-allocate with capacity 1,048,576
+- Custom u32-based hasher
+- Run in separate thread via `spawn_blocking()`
+
+### Should We Follow Their Approach?
+
+**Pros of their approach:**
+- Simpler code, fewer edge cases
+- Proven correct (Bitcoin Core algorithm port)
+- Fast enough with optimizations (sub-100ms for full rebuild)
+
+**Pros of incremental:**
+- Lower latency for small changes
+- Less CPU spike on each update
+- Better for very high tx throughput
+
+**Recommendation:** Start with their approach (rebuild with optimizations), measure performance. Only add incremental if needed.
+
+### Simplified Algorithm (from mempool.space)
+
+```
+1. Build audit_pool: Map<uid, AuditTransaction>
+2. set_relatives(): compute ancestors for each tx
+3. Sort by ancestor_score descending
+4. while mempool not empty:
+     a. Pick best from (stack, modified_queue)
+     b. If ancestors not yet selected, select them first
+     c. Add to current block
+     d. If block full, start new block
+     e. update_descendants(): recalc scores, add to modified_queue
+5. Return blocks
+```
+
+### Key Optimization: Ancestor Score
+
+```rust
+ancestor_score = (tx.fee + sum(ancestor.fee)) / (tx.weight + sum(ancestor.weight))
+```
+
+This single metric captures CPFP naturally - a high-fee child boosts its low-fee parents by being evaluated as a package.
+
+## Revised Implementation Plan
+
+Given mempool.space's approach works well, simplify our design:
+
+### Phase 1: Fast Rebuild (MVP)
+- Use u32 UIDs for txs
+- Compute ancestor scores
+- Greedy selection with modified queue
+- Rebuild on each change (with spawn_blocking)
+
+### Phase 2: Incremental (If Needed)
+- Track which txs changed
+- Only rebuild affected portions
+- Cascade updates through dependency graph
+
+### Phase 3: Further Optimizations
+- Batch updates (coalesce rapid changes)
+- Dirty flag + lazy rebuild
+- Background thread continuous updates
+
+## References
+
+- Bitcoin Core's block assembly: `src/node/miner.cpp`
+- [mempool.space Rust GBT](https://github.com/mempool/mempool/tree/master/rust/gbt/src)
+- [mempool-blocks.ts](https://github.com/mempool/mempool/blob/master/backend/src/api/mempool-blocks.ts)
@@ -5,10 +5,9 @@ use brk_monitor::Mempool;
 use brk_rpc::{Auth, Client};

 fn main() -> Result<()> {
-    // Connect to Bitcoin Core
-    let bitcoin_dir = Client::default_bitcoin_path();
-    // let bitcoin_dir = Path::new("/Volumes/WD_BLACK/bitcoin");
+    brk_logger::init(None)?;

+    let bitcoin_dir = Client::default_bitcoin_path();
    let client = Client::new(
        Client::default_url(),
        Auth::CookieFile(bitcoin_dir.join(".cookie")),
@@ -16,19 +15,58 @@ fn main() -> Result<()> {

    let mempool = Mempool::new(&client);

+    // Start mempool sync in background thread
    let mempool_clone = mempool.clone();
    thread::spawn(move || {
        mempool_clone.start();
    });

-    // Access from main thread
+    // Poll and display stats every 5 seconds
    loop {
        thread::sleep(Duration::from_secs(5));
-        let txs = mempool.get_txs();
-        println!("mempool_tx_count: {}", txs.len());
-        let addresses = mempool.get_addresses();
-        println!("mempool_address_count: {}", addresses.len());
-    }

-    // Ok(())
+        // Basic mempool info
+        let info = mempool.get_info();
+        let block_stats = mempool.get_block_stats();
+        let total_fees: u64 = block_stats.iter().map(|s| u64::from(s.total_fee)).sum();
+        println!("\n=== Mempool Info ===");
+        println!("  Transactions: {}", info.count);
+        println!("  Total vsize:  {} vB", info.vsize);
+        println!(
+            "  Total fees:   {:.4} BTC",
+            total_fees as f64 / 100_000_000.0
+        );
+
+        // Fee recommendations (like mempool.space)
+        let fees = mempool.get_fees();
+        println!("\n=== Recommended Fees (sat/vB) ===");
+        println!("  No Priority     {:.4}", f64::from(fees.economy_fee));
+        println!("  Low Priority    {:.4}", f64::from(fees.hour_fee));
+        println!("  Medium Priority {:.4}", f64::from(fees.half_hour_fee));
+        println!("  High Priority   {:.4}", f64::from(fees.fastest_fee));
+
+        // Projected blocks (like mempool.space)
+        if !block_stats.is_empty() {
+            println!("\n=== Projected Blocks ===");
+            for (i, stats) in block_stats.iter().enumerate() {
+                let total_fee_btc = u64::from(stats.total_fee) as f64 / 100_000_000.0;
+                println!(
+                    "  Block {}: ~{:.4} sat/vB, {:.4}-{:.4} sat/vB, {:.3} BTC, {} txs",
+                    i + 1,
+                    f64::from(stats.median_fee_rate()),
+                    f64::from(stats.min_fee_rate()),
+                    f64::from(stats.max_fee_rate()),
+                    total_fee_btc,
+                    stats.tx_count,
+                );
+            }
+        }
+
+        // Address tracking stats
+        let addresses = mempool.get_addresses();
+        println!("\n=== Address Tracking ===");
+        println!("  Addresses with pending txs: {}", addresses.len());
+
+        println!("\n----------------------------------------");
+    }
 }
@@ -1,234 +1,10 @@
-use std::{sync::Arc, thread, time::Duration};
-
-use brk_error::Result;
-use brk_rpc::Client;
-use brk_types::{
-    AddressBytes, AddressMempoolStats, MempoolInfo, RecommendedFees, TxWithHex, Txid,
-};
-use derive_deref::Deref;
-use log::error;
-use parking_lot::{RwLock, RwLockReadGuard};
-use rustc_hash::{FxHashMap, FxHashSet};
+//! Bitcoin mempool monitor.
+//!
+//! Provides real-time mempool tracking with:
+//! - Fee estimation via projected blocks
+//! - Address mempool stats
+//! - CPFP-aware block building

 mod mempool;

-use mempool::{ProjectedBlocks, TxGraph};
-
-const MAX_FETCHES_PER_CYCLE: usize = 10_000;
-
-///
-/// Mempool monitor
-///
-/// Thread safe and free to clone
-///
-#[derive(Clone, Deref)]
-pub struct Mempool(Arc<MempoolInner>);
-
-impl Mempool {
-    pub fn new(client: &Client) -> Self {
-        Self(Arc::new(MempoolInner::new(client.clone())))
-    }
-}
-
-pub struct MempoolInner {
-    client: Client,
-    info: RwLock<MempoolInfo>,
-    fees: RwLock<RecommendedFees>,
-    graph: RwLock<TxGraph>,
-    projected_blocks: RwLock<ProjectedBlocks>,
-    txs: RwLock<FxHashMap<Txid, TxWithHex>>,
-    addresses: RwLock<FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>>,
-}
-
-impl MempoolInner {
-    pub fn new(client: Client) -> Self {
-        Self {
-            client,
-            info: RwLock::new(MempoolInfo::default()),
-            fees: RwLock::new(RecommendedFees::default()),
-            graph: RwLock::new(TxGraph::new()),
-            projected_blocks: RwLock::new(ProjectedBlocks::default()),
-            txs: RwLock::new(FxHashMap::default()),
-            addresses: RwLock::new(FxHashMap::default()),
-        }
-    }
-
-    pub fn get_info(&self) -> MempoolInfo {
-        self.info.read().clone()
-    }
-
-    pub fn get_fees(&self) -> RecommendedFees {
-        self.fees.read().clone()
-    }
-
-    pub fn get_projected_blocks(&self) -> ProjectedBlocks {
-        self.projected_blocks.read().clone()
-    }
-
-    pub fn get_txs(&self) -> RwLockReadGuard<'_, FxHashMap<Txid, TxWithHex>> {
-        self.txs.read()
-    }
-
-    pub fn get_addresses(
-        &self,
-    ) -> RwLockReadGuard<'_, FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>> {
-        self.addresses.read()
-    }
-
-    /// Start an infinite update loop with a 1 second interval
-    pub fn start(&self) {
-        loop {
-            if let Err(e) = self.update() {
-                error!("Error updating mempool: {}", e);
-            }
-            thread::sleep(Duration::from_secs(1));
-        }
-    }
-
-    pub fn update(&self) -> Result<()> {
-        let current_txids = self
-            .client
-            .get_raw_mempool()?
-            .into_iter()
-            .collect::<FxHashSet<_>>();
-
-        let new_txs = self.fetch_new_txs(&current_txids);
-        let has_changes = self.apply_changes(&current_txids, &new_txs);
-
-        if has_changes {
-            self.rebuild_projected_blocks();
-        }
-
-        Ok(())
-    }
-
-    /// Fetch transactions that are new to our mempool
-    fn fetch_new_txs(&self, current_txids: &FxHashSet<Txid>) -> FxHashMap<Txid, TxWithHex> {
-        let txs = self.txs.read();
-        current_txids
-            .iter()
-            .filter(|txid| !txs.contains_key(*txid))
-            .take(MAX_FETCHES_PER_CYCLE)
-            .cloned()
-            .collect::<Vec<_>>()
-            .into_iter()
-            .filter_map(|txid| {
-                self.client
-                    .get_mempool_transaction(&txid)
-                    .ok()
-                    .map(|tx| (txid, tx))
-            })
-            .collect()
-    }
-
-    /// Apply transaction additions and removals, returns true if there were changes
-    fn apply_changes(
-        &self,
-        current_txids: &FxHashSet<Txid>,
-        new_txs: &FxHashMap<Txid, TxWithHex>,
-    ) -> bool {
-        let mut info = self.info.write();
-        let mut graph = self.graph.write();
-        let mut txs = self.txs.write();
-        let mut addresses = self.addresses.write();
-
-        let mut had_removals = false;
-        let had_additions = !new_txs.is_empty();
-
-        // Remove transactions no longer in mempool
-        txs.retain(|txid, tx_with_hex| {
-            if current_txids.contains(txid) {
-                return true;
-            }
-
-            had_removals = true;
-            let tx = tx_with_hex.tx();
-
-            info.remove(tx);
-            graph.remove(txid);
-            Self::update_address_stats_on_removal(tx, txid, &mut addresses);
-
-            false
-        });
-
-        // Add new transactions
-        for (txid, tx_with_hex) in new_txs {
-            let tx = tx_with_hex.tx();
-
-            info.add(tx);
-            graph.insert(tx);
-            Self::update_address_stats_on_addition(tx, txid, &mut addresses);
-        }
-        txs.extend(new_txs.clone());
-
-        had_removals || had_additions
-    }
-
-    /// Rebuild projected blocks and update recommended fees
-    fn rebuild_projected_blocks(&self) {
-        let graph = self.graph.read();
-        let projected = ProjectedBlocks::build(&graph);
-        let fees = projected.recommended_fees();
-
-        *self.projected_blocks.write() = projected;
-        *self.fees.write() = fees;
-    }
-
-    fn update_address_stats_on_removal(
-        tx: &brk_types::Transaction,
-        txid: &Txid,
-        addresses: &mut FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>,
-    ) {
-        // Inputs: undo "sending" state
-        tx.input
-            .iter()
-            .flat_map(|txin| txin.prevout.as_ref())
-            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
-            .for_each(|(txout, bytes)| {
-                let (stats, set) = addresses.entry(bytes).or_default();
-                set.remove(txid);
-                stats.sent(txout);
-                stats.update_tx_count(set.len() as u32);
-            });
-
-        // Outputs: undo "receiving" state
-        tx.output
-            .iter()
-            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
-            .for_each(|(txout, bytes)| {
-                let (stats, set) = addresses.entry(bytes).or_default();
-                set.remove(txid);
-                stats.received(txout);
-                stats.update_tx_count(set.len() as u32);
-            });
-    }
-
-    fn update_address_stats_on_addition(
-        tx: &brk_types::Transaction,
-        txid: &Txid,
-        addresses: &mut FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>,
-    ) {
-        // Inputs: mark as "sending"
-        tx.input
-            .iter()
-            .flat_map(|txin| txin.prevout.as_ref())
-            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
-            .for_each(|(txout, bytes)| {
-                let (stats, set) = addresses.entry(bytes).or_default();
-                set.insert(txid.clone());
-                stats.sending(txout);
-                stats.update_tx_count(set.len() as u32);
-            });
-
-        // Outputs: mark as "receiving"
-        tx.output
-            .iter()
-            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
-            .for_each(|(txout, bytes)| {
-                let (stats, set) = addresses.entry(bytes).or_default();
-                set.insert(txid.clone());
-                stats.receiving(txout);
-                stats.update_tx_count(set.len() as u32);
-            });
-    }
-}
+pub use mempool::{BlockStats, Mempool, MempoolInner, ProjectedSnapshot};
@@ -0,0 +1,164 @@
+use std::ops::{Index, IndexMut};
+
+use brk_types::{Sats, VSize};
+use smallvec::SmallVec;
+
+use crate::mempool::{MempoolTxIndex, PoolIndex};
+
+/// Compare ancestor fee rates using cross-multiplication (avoids f64 division).
+/// Returns true if (fee_a / vsize_a) > (fee_b / vsize_b).
+#[inline]
+fn has_higher_fee_rate(fee_a: Sats, vsize_a: VSize, fee_b: Sats, vsize_b: VSize) -> bool {
+    // Cross multiply: fee_a/vsize_a > fee_b/vsize_b  ⟺  fee_a * vsize_b > fee_b * vsize_a
+    let score_a = u64::from(fee_a) as u128 * u64::from(vsize_b) as u128;
+    let score_b = u64::from(fee_b) as u128 * u64::from(vsize_a) as u128;
+    score_a > score_b
+}
+
+/// Type-safe wrapper around Vec<AuditTx> that only allows PoolIndex access.
+pub struct Pool(Vec<AuditTx>);
+
+impl Pool {
+    pub fn new(txs: Vec<AuditTx>) -> Self {
+        Self(txs)
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl Index<PoolIndex> for Pool {
+    type Output = AuditTx;
+
+    #[inline]
+    fn index(&self, idx: PoolIndex) -> &Self::Output {
+        &self.0[idx.as_usize()]
+    }
+}
+
+impl IndexMut<PoolIndex> for Pool {
+    #[inline]
+    fn index_mut(&mut self, idx: PoolIndex) -> &mut Self::Output {
+        &mut self.0[idx.as_usize()]
+    }
+}
+
+/// Lightweight transaction for block building.
+/// Created fresh each rebuild, discarded after.
+pub struct AuditTx {
+    /// Original entries index (for final output)
+    pub entries_idx: MempoolTxIndex,
+    /// Pool index (for internal graph traversal)
+    pub pool_idx: PoolIndex,
+    pub fee: Sats,
+    pub vsize: VSize,
+    /// In-mempool parent pool indices
+    pub parents: SmallVec<[PoolIndex; 4]>,
+    /// In-mempool child pool indices
+    pub children: SmallVec<[PoolIndex; 8]>,
+    /// Cumulative fee (self + all ancestors)
+    pub ancestor_fee: Sats,
+    /// Cumulative vsize (self + all ancestors)
+    pub ancestor_vsize: VSize,
+    /// Already selected into a block
+    pub used: bool,
+    /// Already in modified priority queue
+    pub in_modified: bool,
+}
+
+impl AuditTx {
+    /// Create AuditTx with pre-computed ancestor values from Bitcoin Core.
+    pub fn new_with_ancestors(
+        entries_idx: MempoolTxIndex,
+        pool_idx: PoolIndex,
+        fee: Sats,
+        vsize: VSize,
+        ancestor_fee: Sats,
+        ancestor_vsize: VSize,
+    ) -> Self {
+        Self {
+            entries_idx,
+            pool_idx,
+            fee,
+            vsize,
+            parents: SmallVec::new(),
+            children: SmallVec::new(),
+            ancestor_fee,
+            ancestor_vsize,
+            used: false,
+            in_modified: false,
+        }
+    }
+
+    #[inline]
+    pub fn has_higher_score_than(&self, other: &Self) -> bool {
+        has_higher_fee_rate(
+            self.ancestor_fee,
+            self.ancestor_vsize,
+            other.ancestor_fee,
+            other.ancestor_vsize,
+        )
+    }
+}
+
+/// Priority queue entry for the modified queue.
+/// Stores a snapshot of ancestor values at time of insertion.
+#[derive(Clone, Copy)]
+pub struct TxPriority {
+    /// Pool index (for indexing into pool array)
+    pub pool_idx: PoolIndex,
+    /// Snapshot of ancestor fee at insertion time
+    pub ancestor_fee: Sats,
+    /// Snapshot of ancestor vsize at insertion time
+    pub ancestor_vsize: VSize,
+}
+
+impl TxPriority {
+    pub fn new(tx: &AuditTx) -> Self {
+        Self {
+            pool_idx: tx.pool_idx,
+            ancestor_fee: tx.ancestor_fee,
+            ancestor_vsize: tx.ancestor_vsize,
+        }
+    }
+
+    #[inline]
+    pub fn has_higher_score_than(&self, other: &Self) -> bool {
+        has_higher_fee_rate(
+            self.ancestor_fee,
+            self.ancestor_vsize,
+            other.ancestor_fee,
+            other.ancestor_vsize,
+        )
+    }
+}
+
+impl PartialEq for TxPriority {
+    fn eq(&self, other: &Self) -> bool {
+        self.pool_idx == other.pool_idx
+    }
+}
+
+impl Eq for TxPriority {}
+
+impl PartialOrd for TxPriority {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for TxPriority {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        // Higher score = higher priority (for max-heap)
+        if self.has_higher_score_than(other) {
+            std::cmp::Ordering::Greater
+        } else if other.has_higher_score_than(self) {
+            std::cmp::Ordering::Less
+        } else {
+            // Tiebreaker: lower index first (deterministic)
+            other.pool_idx.cmp(&self.pool_idx)
+        }
+    }
+}
@@ -0,0 +1,118 @@
+use brk_types::TxidPrefix;
+use rustc_hash::FxHashMap;
+
+use super::audit::{AuditTx, Pool};
+use super::selection::select_into_blocks;
+use crate::mempool::{MempoolEntry, MempoolTxIndex, PoolIndex, SelectedTx};
+
+/// Number of projected blocks to build
+const NUM_PROJECTED_BLOCKS: usize = 8;
+
+/// Estimated txs per block (for partial sort optimization)
+const TXS_PER_BLOCK: usize = 4000;
+
+/// Build projected blocks from mempool entries.
+///
+/// Returns SelectedTx (with effective fee rate) grouped by block, in mining priority order.
+pub fn build_projected_blocks(entries: &[Option<MempoolEntry>]) -> Vec<Vec<SelectedTx>> {
+    // Collect live entries
+    let live: Vec<(MempoolTxIndex, &MempoolEntry)> = entries
+        .iter()
+        .enumerate()
+        .filter_map(|(i, opt)| opt.as_ref().map(|e| (MempoolTxIndex::from(i), e)))
+        .collect();
+
+    if live.is_empty() {
+        return Vec::new();
+    }
+
+    // Build AuditTx pool with pre-computed ancestor values from Bitcoin Core
+    let mut pool = Pool::new(build_audit_pool(&live));
+
+    // Sort by ancestor score (partial sort for efficiency)
+    let sorted = partial_sort_by_score(&pool);
+
+    // Run selection algorithm
+    select_into_blocks(&mut pool, sorted, NUM_PROJECTED_BLOCKS)
+}
+
+/// Build the AuditTx pool with parent/child relationships.
+/// AuditTx.parents and .children store pool indices (for graph traversal).
+/// AuditTx.entries_idx stores the original entries index (for final output).
+/// Uses Bitcoin Core's pre-computed ancestor values (correct, no double-counting).
+fn build_audit_pool(live: &[(MempoolTxIndex, &MempoolEntry)]) -> Vec<AuditTx> {
+    // Create mapping from TxidPrefix to pool index
+    let prefix_to_pool_idx: FxHashMap<TxidPrefix, PoolIndex> = live
+        .iter()
+        .enumerate()
+        .map(|(pool_idx, (_, entry))| (entry.txid_prefix(), PoolIndex::from(pool_idx)))
+        .collect();
+
+    // Build pool with parent relationships
+    // Use Bitcoin Core's pre-computed ancestor_fee and ancestor_vsize
+    let mut pool: Vec<AuditTx> = live
+        .iter()
+        .enumerate()
+        .map(|(pool_idx, (entries_idx, entry))| {
+            let pool_idx = PoolIndex::from(pool_idx);
+            let mut tx = AuditTx::new_with_ancestors(
+                *entries_idx,
+                pool_idx,
+                entry.fee,
+                entry.vsize,
+                entry.ancestor_fee,
+                entry.ancestor_vsize,
+            );
+
+            // Find in-mempool parents from depends list (provided by Bitcoin Core)
+            for parent_prefix in &entry.depends {
+                if let Some(&parent_pool_idx) = prefix_to_pool_idx.get(parent_prefix) {
+                    tx.parents.push(parent_pool_idx);
+                }
+            }
+
+            tx
+        })
+        .collect();
+
+    // Build child relationships (reverse of parents)
+    for pool_idx in 0..pool.len() {
+        let parents = pool[pool_idx].parents.clone();
+        for parent_pool_idx in parents {
+            pool[parent_pool_idx.as_usize()].children.push(PoolIndex::from(pool_idx));
+        }
+    }
+
+    pool
+}
+
+/// Partial sort: only fully sort the top N txs needed for blocks.
+/// Returns pool indices sorted by ancestor score.
+fn partial_sort_by_score(pool: &Pool) -> Vec<PoolIndex> {
+    let mut indices: Vec<PoolIndex> = (0..pool.len()).map(PoolIndex::from).collect();
+    let needed = NUM_PROJECTED_BLOCKS * TXS_PER_BLOCK;
+
+    // Comparator: descending by score, then ascending by index (deterministic tiebreaker)
+    let cmp = |a: &PoolIndex, b: &PoolIndex| -> std::cmp::Ordering {
+        let tx_a = &pool[*a];
+        let tx_b = &pool[*b];
+        if tx_b.has_higher_score_than(tx_a) {
+            std::cmp::Ordering::Greater
+        } else if tx_a.has_higher_score_than(tx_b) {
+            std::cmp::Ordering::Less
+        } else {
+            a.cmp(b)
+        }
+    };
+
+    if indices.len() > needed {
+        // Partition: move top `needed` to front (unordered), then sort just those
+        indices.select_nth_unstable_by(needed, cmp);
+        indices[..needed].sort_unstable_by(cmp);
+        indices.truncate(needed);
+    } else {
+        indices.sort_unstable_by(cmp);
+    }
+
+    indices
+}
@@ -0,0 +1,5 @@
+mod audit;
+mod build;
+mod selection;
+
+pub use build::build_projected_blocks;
@@ -0,0 +1,278 @@
+use std::collections::BinaryHeap;
+
+use brk_types::FeeRate;
+
+use super::audit::{Pool, TxPriority};
+use crate::mempool::{PoolIndex, SelectedTx};
+
+/// Target vsize per block (~1MB, derived from 4MW weight limit)
+const BLOCK_VSIZE_LIMIT: u64 = 1_000_000;
+
+/// Select transactions into blocks using the two-source algorithm.
+///
+/// Takes pool indices (sorted by score), returns SelectedTx with effective fee rate at selection time.
+pub fn select_into_blocks(
+    pool: &mut Pool,
+    sorted_pool_indices: Vec<PoolIndex>,
+    num_blocks: usize,
+) -> Vec<Vec<SelectedTx>> {
+    let mut blocks: Vec<Vec<SelectedTx>> = Vec::with_capacity(num_blocks);
+    let mut current_block: Vec<SelectedTx> = Vec::new();
+    let mut current_vsize: u64 = 0;
+
+    let mut sorted_iter = sorted_pool_indices.into_iter().peekable();
+    let mut modified_queue: BinaryHeap<TxPriority> = BinaryHeap::new();
+
+    'outer: loop {
+        // Pick best candidate from either sorted list or modified queue
+        let best_pool_idx = pick_best_candidate(pool, &mut sorted_iter, &mut modified_queue);
+        let Some(pool_idx) = best_pool_idx else {
+            break;
+        };
+
+        // Skip if already used
+        if pool[pool_idx].used {
+            continue;
+        }
+
+        // Capture the package rate BEFORE selecting ancestors
+        // This is the rate that justified this tx (and its ancestors) for inclusion
+        let package_rate = {
+            let tx = &pool[pool_idx];
+            FeeRate::from((tx.ancestor_fee, tx.ancestor_vsize))
+        };
+
+        // Select this tx and all its unselected ancestors
+        let selected = select_with_ancestors(pool, pool_idx);
+
+        for sel_pool_idx in selected {
+            let tx = &pool[sel_pool_idx];
+            let tx_vsize = u64::from(tx.vsize);
+
+            // Check if tx fits in current block
+            if current_vsize + tx_vsize > BLOCK_VSIZE_LIMIT && !current_block.is_empty() {
+                blocks.push(std::mem::take(&mut current_block));
+                current_vsize = 0;
+
+                if blocks.len() >= num_blocks {
+                    // Early exit - we have enough blocks
+                    break 'outer;
+                }
+            }
+
+            // Effective fee rate = the package rate at selection time.
+            // This is the mining score that determined which block this tx lands in.
+            // For CPFP, both parent and child get the same package rate (the child's score).
+            current_block.push(SelectedTx {
+                entries_idx: tx.entries_idx,
+                effective_fee_rate: package_rate,
+            });
+            current_vsize += tx_vsize;
+
+            // Update descendants' ancestor scores
+            update_descendants(pool, sel_pool_idx, &mut modified_queue);
+        }
+    }
+
+    // Don't forget the last block
+    if !current_block.is_empty() && blocks.len() < num_blocks {
+        blocks.push(current_block);
+    }
+
+    // Post-process: fix fee rate ordering violations between adjacent blocks.
+    // This handles cases where a tx's score improved after its target block was full.
+    fix_block_ordering(&mut blocks);
+
+    // Log how many txs were left unselected
+    let total_selected: usize = blocks.iter().map(|b| b.len()).sum();
+    log::debug!(
+        "Selected {} txs into {} blocks, modified_queue has {} remaining",
+        total_selected,
+        blocks.len(),
+        modified_queue.len()
+    );
+
+    blocks
+}
+
+/// Pick the best candidate from sorted list or modified queue.
+/// Returns a pool index.
+fn pick_best_candidate(
+    pool: &Pool,
+    sorted_iter: &mut std::iter::Peekable<std::vec::IntoIter<PoolIndex>>,
+    modified_queue: &mut BinaryHeap<TxPriority>,
+) -> Option<PoolIndex> {
+    // Skip used txs in sorted iterator
+    while sorted_iter.peek().is_some_and(|&idx| pool[idx].used) {
+        sorted_iter.next();
+    }
+
+    // Skip used txs and stale entries in modified queue.
+    // A tx can be pushed multiple times as its score improves (when different ancestors are selected).
+    // For example: tx C depends on A and B. When A is selected, C is pushed with score 2.0.
+    // When B is selected, C is pushed again with score 4.0. The queue now has two entries for C.
+    // We skip the stale 2.0 entry and use the current 4.0 entry.
+    while let Some(p) = modified_queue.peek() {
+        let tx = &pool[p.pool_idx];
+        if tx.used {
+            modified_queue.pop();
+            continue;
+        }
+        // Check if this queue entry has outdated snapshot (a newer entry exists with better score)
+        if p.ancestor_fee != tx.ancestor_fee || p.ancestor_vsize != tx.ancestor_vsize {
+            modified_queue.pop();
+            continue;
+        }
+        break;
+    }
+
+    let sorted_best = sorted_iter.peek().map(|&idx| &pool[idx]);
+    let modified_best = modified_queue.peek().map(|p| &pool[p.pool_idx]);
+
+    match (sorted_best, modified_best) {
+        (None, None) => None,
+        (Some(_), None) => sorted_iter.next(),
+        (None, Some(_)) => {
+            let p = modified_queue.pop().unwrap();
+            Some(p.pool_idx)
+        }
+        (Some(sorted_tx), Some(modified_tx)) => {
+            // Compare CURRENT scores from pool (not stale snapshots)
+            if sorted_tx.has_higher_score_than(modified_tx) {
+                sorted_iter.next()
+            } else {
+                let p = modified_queue.pop().unwrap();
+                Some(p.pool_idx)
+            }
+        }
+    }
+}
+
+/// Select a tx and all its unselected ancestors (topological order).
+/// Takes and returns pool indices.
+fn select_with_ancestors(pool: &mut Pool, pool_idx: PoolIndex) -> Vec<PoolIndex> {
+    let mut to_select: Vec<PoolIndex> = Vec::new();
+    let mut stack = vec![pool_idx];
+
+    // DFS to find all unselected ancestors
+    while let Some(current) = stack.pop() {
+        let tx = &pool[current];
+        if tx.used {
+            continue;
+        }
+
+        // Push unselected parents onto stack (process parents first)
+        let has_unselected_parents = tx.parents.iter().any(|&p| !pool[p].used);
+        if has_unselected_parents {
+            stack.push(current); // Re-add self to process after parents
+            for &parent in &tx.parents {
+                if !pool[parent].used {
+                    stack.push(parent);
+                }
+            }
+        } else {
+            // All parents selected, can select this one
+            if !pool[current].used {
+                pool[current].used = true;
+                to_select.push(current);
+            }
+        }
+    }
+
+    to_select
+}
+
+/// Fix fee rate ordering violations between blocks.
+/// Swaps txs between adjacent blocks until Block N's min >= Block N+1's max.
+fn fix_block_ordering(blocks: &mut [Vec<SelectedTx>]) {
+    // Iterate until no more swaps needed
+    let mut changed = true;
+    let mut iterations = 0;
+    const MAX_ITERATIONS: usize = 100; // Prevent infinite loops
+
+    while changed && iterations < MAX_ITERATIONS {
+        changed = false;
+        iterations += 1;
+
+        for i in 0..blocks.len().saturating_sub(1) {
+            // Find min in block i and max in block i+1
+            let Some(curr_min_idx) = blocks[i]
+                .iter()
+                .enumerate()
+                .min_by_key(|(_, s)| s.effective_fee_rate)
+                .map(|(idx, _)| idx)
+            else {
+                continue;
+            };
+
+            let Some(next_max_idx) = blocks[i + 1]
+                .iter()
+                .enumerate()
+                .max_by_key(|(_, s)| s.effective_fee_rate)
+                .map(|(idx, _)| idx)
+            else {
+                continue;
+            };
+
+            let curr_min = blocks[i][curr_min_idx].effective_fee_rate;
+            let next_max = blocks[i + 1][next_max_idx].effective_fee_rate;
+
+            // If violation exists, swap the two txs
+            if next_max > curr_min {
+                // Swap: move high-fee tx to earlier block, low-fee tx to later block
+                let high_tx = blocks[i + 1].swap_remove(next_max_idx);
+                let low_tx = blocks[i].swap_remove(curr_min_idx);
+                blocks[i].push(high_tx);
+                blocks[i + 1].push(low_tx);
+                changed = true;
+            }
+        }
+    }
+
+    if iterations >= MAX_ITERATIONS {
+        log::warn!("fix_block_ordering: reached max iterations, some violations may remain");
+    }
+}
+
+/// Update descendants' ancestor scores after selecting a tx.
+/// Takes a pool index.
+fn update_descendants(
+    pool: &mut Pool,
+    selected_pool_idx: PoolIndex,
+    modified_queue: &mut BinaryHeap<TxPriority>,
+) {
+    let selected_fee = pool[selected_pool_idx].fee;
+    let selected_vsize = pool[selected_pool_idx].vsize;
+
+    // Track visited to avoid double-subtracting in diamond patterns
+    let mut visited = rustc_hash::FxHashSet::default();
+
+    // BFS through children (children are pool indices)
+    let mut stack: Vec<PoolIndex> = pool[selected_pool_idx].children.to_vec();
+
+    while let Some(child_idx) = stack.pop() {
+        // Skip if already visited (handles diamond patterns)
+        if !visited.insert(child_idx) {
+            continue;
+        }
+
+        let child = &mut pool[child_idx];
+
+        if child.used {
+            continue;
+        }
+
+        // Subtract selected tx from ancestor totals
+        child.ancestor_fee -= selected_fee;
+        child.ancestor_vsize -= selected_vsize;
+
+        // Always re-push to modified queue with updated score.
+        // This may create duplicates, but we handle that by checking
+        // if the tx is used or if the snapshot is stale when popping.
+        modified_queue.push(TxPriority::new(child));
+        child.in_modified = true;
+
+        // Continue to grandchildren
+        stack.extend(child.children.iter().copied());
+    }
+}
@@ -1,62 +1,55 @@
-use brk_types::{FeeRate, Sats, Transaction, Txid, VSize, Vout};
-use rustc_hash::FxHashSet;
+use brk_types::{FeeRate, MempoolEntryInfo, Sats, Txid, TxidPrefix, VSize};

-/// (txid, vout) tuple identifying an unspent output in the mempool
-pub type MempoolOutpoint = (Txid, Vout);
-
-/// A mempool transaction with its dependency metadata
+/// A mempool transaction entry.
+///
+/// Stores only the data needed for fee estimation and block building.
+/// Ancestor values are pre-computed by Bitcoin Core (correctly handling shared ancestors).
 #[derive(Debug, Clone)]
 pub struct MempoolEntry {
    pub txid: Txid,
    pub fee: Sats,
    pub vsize: VSize,
-
-    /// Outpoints this tx spends (inputs)
-    pub spends: Vec<MempoolOutpoint>,
-
-    /// Txids of unconfirmed ancestors (parents, grandparents, etc.)
-    pub ancestors: FxHashSet<Txid>,
-
-    /// Cumulative fee of this tx + all ancestors
+    /// Pre-computed ancestor fee (self + all ancestors, no double-counting)
    pub ancestor_fee: Sats,
-
-    /// Cumulative vsize of this tx + all ancestors
+    /// Pre-computed ancestor vsize (self + all ancestors, no double-counting)
    pub ancestor_vsize: VSize,
+    /// Parent txid prefixes (transactions this tx depends on)
+    pub depends: Vec<TxidPrefix>,
 }

 impl MempoolEntry {
-    pub fn new(tx: &Transaction) -> Self {
-        let txid = tx.txid.clone();
-        let fee = tx.fee;
-        let vsize = tx.vsize();
-
-        let spends = tx
-            .input
-            .iter()
-            .map(|txin| (txin.txid.clone(), txin.vout))
-            .collect();
-
+    pub fn from_info(info: &MempoolEntryInfo) -> Self {
        Self {
-            txid,
-            fee,
-            vsize,
-            spends,
-            ancestors: FxHashSet::default(),
-            ancestor_fee: fee,
-            ancestor_vsize: vsize,
+            txid: info.txid.clone(),
+            fee: info.fee,
+            vsize: VSize::from(info.vsize),
+            ancestor_fee: info.ancestor_fee,
+            ancestor_vsize: VSize::from(info.ancestor_size),
+            depends: info.depends.iter().map(TxidPrefix::from).collect(),
        }
    }

-    /// Individual fee rate (without ancestors)
    #[inline]
    pub fn fee_rate(&self) -> FeeRate {
        FeeRate::from((self.fee, self.vsize))
    }

-    /// Ancestor fee rate (fee + ancestors_fee) / (vsize + ancestors_vsize)
-    /// This is the effective mining priority
+    /// Ancestor fee rate (package rate for CPFP)
    #[inline]
    pub fn ancestor_fee_rate(&self) -> FeeRate {
        FeeRate::from((self.ancestor_fee, self.ancestor_vsize))
    }
+
+    /// Effective fee rate for display - the rate that justified this tx's inclusion.
+    /// For CPFP parents, this is their ancestor_fee_rate (child paying for them).
+    /// For regular txs, this is their own fee_rate.
+    #[inline]
+    pub fn effective_fee_rate(&self) -> FeeRate {
+        std::cmp::max(self.fee_rate(), self.ancestor_fee_rate())
+    }
+
+    #[inline]
+    pub fn txid_prefix(&self) -> TxidPrefix {
+        TxidPrefix::from(&self.txid)
+    }
 }
@@ -1,175 +0,0 @@
-use brk_types::{Sats, Transaction, Txid, VSize, Vout};
-use rustc_hash::{FxHashMap, FxHashSet};
-
-use super::entry::MempoolOutpoint;
-use super::MempoolEntry;
-
-/// Transaction dependency graph for the mempool
-///
-/// Tracks parent-child relationships and computes ancestor feerates
-/// for proper CPFP (Child-Pays-For-Parent) handling.
-#[derive(Debug, Default)]
-pub struct TxGraph {
-    /// All mempool entries by txid
-    entries: FxHashMap<Txid, MempoolEntry>,
-
-    /// Maps outpoint -> txid that created it (for finding parents)
-    outpoint_to_tx: FxHashMap<MempoolOutpoint, Txid>,
-
-    /// Maps txid -> txids that spend its outputs (children)
-    children: FxHashMap<Txid, FxHashSet<Txid>>,
-}
-
-impl TxGraph {
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    pub fn entries(&self) -> &FxHashMap<Txid, MempoolEntry> {
-        &self.entries
-    }
-
-    pub fn len(&self) -> usize {
-        self.entries.len()
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.entries.is_empty()
-    }
-
-    /// Add a transaction to the graph
-    pub fn insert(&mut self, tx: &Transaction) {
-        let mut entry = MempoolEntry::new(tx);
-
-        // Find in-mempool parents and build ancestor set
-        let parents = self.find_parents(&entry.spends);
-        entry.ancestors = self.compute_ancestors(&parents);
-
-        // Compute ancestor fee/vsize
-        let (ancestor_fee, ancestor_vsize) = self.sum_ancestors(&entry.ancestors);
-        entry.ancestor_fee = entry.fee + ancestor_fee;
-        entry.ancestor_vsize = entry.vsize + ancestor_vsize;
-
-        // Register this tx's outputs
-        for (vout, _) in tx.output.iter().enumerate() {
-            let outpoint = (entry.txid.clone(), Vout::from(vout as u32));
-            self.outpoint_to_tx.insert(outpoint, entry.txid.clone());
-        }
-
-        // Register as child of parents
-        for parent in &parents {
-            self.children
-                .entry(parent.clone())
-                .or_default()
-                .insert(entry.txid.clone());
-        }
-
-        self.entries.insert(entry.txid.clone(), entry);
-    }
-
-    /// Remove a transaction from the graph
-    pub fn remove(&mut self, txid: &Txid) -> Option<MempoolEntry> {
-        let entry = self.entries.remove(txid)?;
-
-        // Remove from outpoint index
-        // Note: We don't know the vout count, so we remove all entries pointing to this txid
-        self.outpoint_to_tx.retain(|_, tx| tx != txid);
-
-        // Remove from children index
-        self.children.remove(txid);
-        for children_set in self.children.values_mut() {
-            children_set.remove(txid);
-        }
-
-        // Update descendants' ancestor data
-        self.update_descendants_after_removal(txid, &entry);
-
-        Some(entry)
-    }
-
-    /// Check if a txid is in the mempool
-    pub fn contains(&self, txid: &Txid) -> bool {
-        self.entries.contains_key(txid)
-    }
-
-    /// Get all txids currently in the graph
-    pub fn txids(&self) -> impl Iterator<Item = &Txid> {
-        self.entries.keys()
-    }
-
-    /// Find which inputs reference in-mempool transactions (parents)
-    fn find_parents(&self, spends: &[MempoolOutpoint]) -> Vec<Txid> {
-        spends
-            .iter()
-            .filter_map(|outpoint| self.outpoint_to_tx.get(outpoint).cloned())
-            .collect()
-    }
-
-    /// Compute full ancestor set (transitive closure)
-    fn compute_ancestors(&self, parents: &[Txid]) -> FxHashSet<Txid> {
-        let mut ancestors = FxHashSet::default();
-        let mut stack: Vec<Txid> = parents.to_vec();
-
-        while let Some(txid) = stack.pop() {
-            if ancestors.insert(txid.clone()) {
-                if let Some(entry) = self.entries.get(&txid) {
-                    stack.extend(entry.ancestors.iter().cloned());
-                }
-            }
-        }
-
-        ancestors
-    }
-
-    /// Sum fee and vsize of all ancestors
-    fn sum_ancestors(&self, ancestors: &FxHashSet<Txid>) -> (Sats, VSize) {
-        ancestors.iter().fold(
-            (Sats::default(), VSize::default()),
-            |(fee, vsize), txid| {
-                if let Some(entry) = self.entries.get(txid) {
-                    (fee + entry.fee, vsize + entry.vsize)
-                } else {
-                    (fee, vsize)
-                }
-            },
-        )
-    }
-
-    /// Update all descendants after removing a transaction
-    fn update_descendants_after_removal(&mut self, removed: &Txid, removed_entry: &MempoolEntry) {
-        // Find all descendants
-        let descendants = self.find_descendants(removed);
-
-        // Update each descendant's ancestor set and cumulative values
-        for desc_txid in descendants {
-            if let Some(desc) = self.entries.get_mut(&desc_txid) {
-                // Remove the removed tx from ancestors
-                desc.ancestors.remove(removed);
-
-                // Subtract the removed tx's contribution
-                desc.ancestor_fee = desc.ancestor_fee - removed_entry.fee;
-                desc.ancestor_vsize = desc.ancestor_vsize - removed_entry.vsize;
-            }
-        }
-    }
-
-    /// Find all descendants of a transaction (children, grandchildren, etc.)
-    fn find_descendants(&self, txid: &Txid) -> Vec<Txid> {
-        let mut descendants = Vec::new();
-        let mut stack = vec![txid.clone()];
-        let mut visited = FxHashSet::default();
-
-        while let Some(current) = stack.pop() {
-            if let Some(children) = self.children.get(&current) {
-                for child in children {
-                    if visited.insert(child.clone()) {
-                        descendants.push(child.clone());
-                        stack.push(child.clone());
-                    }
-                }
-            }
-        }
-
-        descendants
-    }
-}
@@ -1,7 +1,13 @@
+mod block_builder;
 mod entry;
-mod graph;
+mod monitor;
 mod projected_blocks;
+mod types;

-pub use entry::MempoolEntry;
-pub use graph::TxGraph;
-pub use projected_blocks::ProjectedBlocks;
+// Public API
+pub use monitor::{Mempool, MempoolInner};
+pub use projected_blocks::{BlockStats, ProjectedSnapshot};
+
+// Crate-internal (used by submodules)
+pub(crate) use entry::MempoolEntry;
+pub(crate) use types::{MempoolTxIndex, PoolIndex, SelectedTx};
@@ -0,0 +1,341 @@
+use std::{
+    sync::{
+        Arc,
+        atomic::{AtomicBool, AtomicU64, Ordering},
+    },
+    thread,
+    time::{Duration, Instant},
+};
+
+use brk_error::Result;
+use brk_rpc::Client;
+use brk_types::{
+    AddressBytes, AddressMempoolStats, MempoolEntryInfo, MempoolInfo, RecommendedFees, TxWithHex,
+    Txid, TxidPrefix,
+};
+use derive_deref::Deref;
+use log::{error, info};
+use parking_lot::{RwLock, RwLockReadGuard};
+use rustc_hash::{FxHashMap, FxHashSet};
+
+use super::block_builder::build_projected_blocks;
+use super::entry::MempoolEntry;
+use super::projected_blocks::{BlockStats, ProjectedSnapshot};
+use super::types::MempoolTxIndex;
+
+/// Max new txs to fetch full data for per update cycle (for address tracking)
+const MAX_TX_FETCHES_PER_CYCLE: usize = 10_000;
+
+/// Minimum interval between rebuilds (milliseconds)
+const MIN_REBUILD_INTERVAL_MS: u64 = 1000;
+
+/// Block building state - grouped for atomic locking.
+#[derive(Default)]
+struct BlockBuildingState {
+    /// Slot-based entry storage
+    entries: Vec<Option<MempoolEntry>>,
+    /// TxidPrefix -> slot index
+    txid_prefix_to_idx: FxHashMap<TxidPrefix, MempoolTxIndex>,
+    /// Recycled slot indices
+    free_indices: Vec<MempoolTxIndex>,
+}
+
+/// Mempool monitor.
+///
+/// Thread-safe wrapper around `MempoolInner`. Free to clone.
+#[derive(Clone, Deref)]
+pub struct Mempool(Arc<MempoolInner>);
+
+impl Mempool {
+    pub fn new(client: &Client) -> Self {
+        Self(Arc::new(MempoolInner::new(client.clone())))
+    }
+}
+
+/// Inner mempool state and logic.
+pub struct MempoolInner {
+    client: Client,
+
+    // Mempool state
+    info: RwLock<MempoolInfo>,
+    txs: RwLock<FxHashMap<Txid, TxWithHex>>,
+    addresses: RwLock<FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>>,
+
+    // Block building data (single lock for consistency)
+    block_state: RwLock<BlockBuildingState>,
+
+    // Projected blocks snapshot
+    snapshot: RwLock<ProjectedSnapshot>,
+
+    // Rate limiting
+    dirty: AtomicBool,
+    last_rebuild_ms: AtomicU64,
+}
+
+impl MempoolInner {
+    pub fn new(client: Client) -> Self {
+        Self {
+            client,
+            info: RwLock::new(MempoolInfo::default()),
+            txs: RwLock::new(FxHashMap::default()),
+            addresses: RwLock::new(FxHashMap::default()),
+            block_state: RwLock::new(BlockBuildingState::default()),
+            snapshot: RwLock::new(ProjectedSnapshot::default()),
+            dirty: AtomicBool::new(false),
+            last_rebuild_ms: AtomicU64::new(0),
+        }
+    }
+
+    pub fn get_info(&self) -> MempoolInfo {
+        self.info.read().clone()
+    }
+
+    pub fn get_fees(&self) -> RecommendedFees {
+        self.snapshot.read().fees.clone()
+    }
+
+    pub fn get_snapshot(&self) -> ProjectedSnapshot {
+        self.snapshot.read().clone()
+    }
+
+    pub fn get_block_stats(&self) -> Vec<BlockStats> {
+        self.snapshot.read().block_stats.clone()
+    }
+
+    pub fn get_txs(&self) -> RwLockReadGuard<'_, FxHashMap<Txid, TxWithHex>> {
+        self.txs.read()
+    }
+
+    pub fn get_addresses(
+        &self,
+    ) -> RwLockReadGuard<'_, FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>> {
+        self.addresses.read()
+    }
+
+    /// Start an infinite update loop with a 1 second interval.
+    pub fn start(&self) {
+        loop {
+            if let Err(e) = self.update() {
+                error!("Error updating mempool: {}", e);
+            }
+            thread::sleep(Duration::from_secs(1));
+        }
+    }
+
+    /// Sync with Bitcoin Core mempool and rebuild projections if needed.
+    pub fn update(&self) -> Result<()> {
+        // Single RPC call gets all entries with fees
+        let entries_info = self.client.get_raw_mempool_verbose()?;
+
+        let current_txids: FxHashSet<Txid> = entries_info.iter().map(|e| e.txid.clone()).collect();
+
+        // Find new txids and fetch full tx data for address tracking
+        let new_txs = self.fetch_new_txs(&current_txids);
+
+        // Apply changes using the entry info (has fees) and full txs (for addresses)
+        let has_changes = self.apply_changes(&entries_info, &new_txs);
+
+        if has_changes {
+            self.dirty.store(true, Ordering::Release);
+        }
+
+        self.rebuild_if_needed();
+
+        Ok(())
+    }
+
+    /// Fetch full transaction data for new txids (needed for address tracking).
+    fn fetch_new_txs(&self, current_txids: &FxHashSet<Txid>) -> FxHashMap<Txid, TxWithHex> {
+        let txs = self.txs.read();
+        current_txids
+            .iter()
+            .filter(|txid| !txs.contains_key(*txid))
+            .take(MAX_TX_FETCHES_PER_CYCLE)
+            .cloned()
+            .collect::<Vec<_>>()
+            .into_iter()
+            .filter_map(|txid| {
+                self.client
+                    .get_mempool_transaction(&txid)
+                    .ok()
+                    .map(|tx| (txid, tx))
+            })
+            .collect()
+    }
+
+    /// Apply transaction additions and removals. Returns true if there were changes.
+    fn apply_changes(
+        &self,
+        entries_info: &[MempoolEntryInfo],
+        new_txs: &FxHashMap<Txid, TxWithHex>,
+    ) -> bool {
+        // Build lookup map for current entries
+        let current_entries: FxHashMap<TxidPrefix, &MempoolEntryInfo> = entries_info
+            .iter()
+            .map(|e| (TxidPrefix::from(&e.txid), e))
+            .collect();
+
+        let mut info = self.info.write();
+        let mut txs = self.txs.write();
+        let mut addresses = self.addresses.write();
+        let mut block_state = self.block_state.write();
+
+        let mut had_removals = false;
+        let had_additions = !new_txs.is_empty();
+
+        // Remove transactions no longer in mempool
+        txs.retain(|txid, tx_with_hex| {
+            let prefix = TxidPrefix::from(txid);
+            if current_entries.contains_key(&prefix) {
+                return true;
+            }
+
+            had_removals = true;
+            let tx = tx_with_hex.tx();
+
+            info.remove(tx);
+            Self::update_address_stats_on_removal(tx, txid, &mut addresses);
+
+            // Remove from slot-based storage
+            if let Some(idx) = block_state.txid_prefix_to_idx.remove(&prefix) {
+                if let Some(slot) = block_state.entries.get_mut(idx.as_usize()) {
+                    *slot = None;
+                }
+                block_state.free_indices.push(idx);
+            }
+
+            false
+        });
+
+        // Add new transactions
+        for (txid, tx_with_hex) in new_txs {
+            let tx = tx_with_hex.tx();
+            let prefix = TxidPrefix::from(txid);
+
+            // Get the entry info (has fee from Bitcoin Core)
+            let Some(entry_info) = current_entries.get(&prefix) else {
+                continue;
+            };
+
+            let entry = MempoolEntry::from_info(entry_info);
+
+            info.add(tx);
+            Self::update_address_stats_on_addition(tx, txid, &mut addresses);
+
+            // Allocate slot
+            let idx = if let Some(idx) = block_state.free_indices.pop() {
+                block_state.entries[idx.as_usize()] = Some(entry);
+                idx
+            } else {
+                let idx = MempoolTxIndex::from(block_state.entries.len());
+                block_state.entries.push(Some(entry));
+                idx
+            };
+
+            block_state.txid_prefix_to_idx.insert(prefix, idx);
+        }
+        txs.extend(new_txs.clone());
+
+        had_removals || had_additions
+    }
+
+    /// Rebuild projected blocks if dirty and enough time has passed.
+    fn rebuild_if_needed(&self) {
+        if !self.dirty.load(Ordering::Acquire) {
+            return;
+        }
+
+        let now_ms = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .map(|d| d.as_millis() as u64)
+            .unwrap_or(0);
+
+        let last = self.last_rebuild_ms.load(Ordering::Acquire);
+        if now_ms.saturating_sub(last) < MIN_REBUILD_INTERVAL_MS {
+            return;
+        }
+
+        // Attempt to claim the rebuild (atomic compare-exchange)
+        if self
+            .last_rebuild_ms
+            .compare_exchange(last, now_ms, Ordering::AcqRel, Ordering::Relaxed)
+            .is_err()
+        {
+            return; // Another thread is rebuilding
+        }
+
+        self.dirty.store(false, Ordering::Release);
+
+        let i = Instant::now();
+        self.rebuild_projected_blocks();
+        info!("mempool: rebuild_projected_blocks in {:?}", i.elapsed());
+    }
+
+    /// Rebuild projected blocks snapshot.
+    fn rebuild_projected_blocks(&self) {
+        let block_state = self.block_state.read();
+
+        let blocks = build_projected_blocks(&block_state.entries);
+        let snapshot = ProjectedSnapshot::build(blocks, &block_state.entries);
+
+        *self.snapshot.write() = snapshot;
+    }
+
+    fn update_address_stats_on_removal(
+        tx: &brk_types::Transaction,
+        txid: &Txid,
+        addresses: &mut FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>,
+    ) {
+        // Inputs: undo "sending" state
+        tx.input
+            .iter()
+            .flat_map(|txin| txin.prevout.as_ref())
+            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
+            .for_each(|(txout, bytes)| {
+                let (stats, set) = addresses.entry(bytes).or_default();
+                set.remove(txid);
+                stats.sent(txout);
+                stats.update_tx_count(set.len() as u32);
+            });
+
+        // Outputs: undo "receiving" state
+        tx.output
+            .iter()
+            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
+            .for_each(|(txout, bytes)| {
+                let (stats, set) = addresses.entry(bytes).or_default();
+                set.remove(txid);
+                stats.received(txout);
+                stats.update_tx_count(set.len() as u32);
+            });
+    }
+
+    fn update_address_stats_on_addition(
+        tx: &brk_types::Transaction,
+        txid: &Txid,
+        addresses: &mut FxHashMap<AddressBytes, (AddressMempoolStats, FxHashSet<Txid>)>,
+    ) {
+        // Inputs: mark as "sending"
+        tx.input
+            .iter()
+            .flat_map(|txin| txin.prevout.as_ref())
+            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
+            .for_each(|(txout, bytes)| {
+                let (stats, set) = addresses.entry(bytes).or_default();
+                set.insert(txid.clone());
+                stats.sending(txout);
+                stats.update_tx_count(set.len() as u32);
+            });
+
+        // Outputs: mark as "receiving"
+        tx.output
+            .iter()
+            .flat_map(|txout| txout.address_bytes().map(|bytes| (txout, bytes)))
+            .for_each(|(txout, bytes)| {
+                let (stats, set) = addresses.entry(bytes).or_default();
+                set.insert(txid.clone());
+                stats.receiving(txout);
+                stats.update_tx_count(set.len() as u32);
+            });
+    }
+}
@@ -1,135 +1,137 @@
-use std::mem;
+use brk_types::{FeeRate, RecommendedFees, Sats, VSize};

-use brk_types::{FeeRate, RecommendedFees, Sats, Txid, VSize};
-use rustc_hash::FxHashSet;
+use super::{MempoolEntry, MempoolTxIndex, SelectedTx};

-use super::TxGraph;
+/// Minimum fee rate for estimation (sat/vB)
+const MIN_FEE_RATE: f64 = 1.0;

-/// Maximum block weight in weight units (4 million)
-const MAX_BLOCK_WEIGHT: u64 = 4_000_000;
-
-/// Target block vsize (weight / 4)
-const BLOCK_VSIZE_TARGET: u64 = MAX_BLOCK_WEIGHT / 4;
-
-/// Number of projected blocks to build
-const NUM_PROJECTED_BLOCKS: usize = 8;
-
-/// Minimum fee rate (no priority)
-const MIN_FEE_RATE: f64 = 0.1;
-
-/// A projected future block built from mempool transactions
+/// Immutable snapshot of projected blocks.
+/// Stores indices into live entries + pre-computed stats.
 #[derive(Debug, Clone, Default)]
-pub struct ProjectedBlock {
-    pub txids: Vec<Txid>,
+pub struct ProjectedSnapshot {
+    /// Block structure: indices into entries Vec
+    pub blocks: Vec<Vec<MempoolTxIndex>>,
+    /// Pre-computed stats per block
+    pub block_stats: Vec<BlockStats>,
+    /// Pre-computed fee recommendations
+    pub fees: RecommendedFees,
+}
+
+/// Statistics for a single projected block.
+#[derive(Debug, Clone, Default)]
+pub struct BlockStats {
+    pub tx_count: u32,
    pub total_vsize: VSize,
    pub total_fee: Sats,
-    pub min_fee_rate: FeeRate,
-    pub max_fee_rate: FeeRate,
-    pub median_fee_rate: FeeRate,
+    /// Fee rate percentiles: [0%, 10%, 25%, 50%, 75%, 90%, 100%]
+    /// - fee_range[0] = min, fee_range[3] = median, fee_range[6] = max
+    pub fee_range: [FeeRate; 7],
 }

-/// Projected mempool blocks for fee estimation
-#[derive(Debug, Clone, Default)]
-pub struct ProjectedBlocks {
-    pub blocks: Vec<ProjectedBlock>,
+impl BlockStats {
+    pub fn min_fee_rate(&self) -> FeeRate {
+        self.fee_range[0]
+    }
+
+    pub fn median_fee_rate(&self) -> FeeRate {
+        self.fee_range[3]
+    }
+
+    pub fn max_fee_rate(&self) -> FeeRate {
+        self.fee_range[6]
+    }
 }

-impl ProjectedBlocks {
-    /// Build projected blocks from a transaction graph
-    ///
-    /// Simulates how miners would construct blocks by selecting
-    /// transactions with highest ancestor fee rates first.
-    pub fn build(graph: &TxGraph) -> Self {
-        if graph.is_empty() {
-            return Self::default();
-        }
-
-        // Collect entries sorted by ancestor fee rate (descending)
-        let mut sorted: Vec<_> = graph
-            .entries()
+impl ProjectedSnapshot {
+    /// Build snapshot from selected transactions (with effective fee rates) and entries.
+    pub fn build(blocks: Vec<Vec<SelectedTx>>, entries: &[Option<MempoolEntry>]) -> Self {
+        let block_stats: Vec<BlockStats> = blocks
            .iter()
-            .map(|(txid, entry)| {
-                (
-                    txid.clone(),
-                    entry.ancestor_fee_rate(),
-                    entry.vsize,
-                    entry.fee,
-                )
-            })
+            .map(|selected| compute_block_stats(selected, entries))
            .collect();

-        sorted.sort_by(|a, b| b.1.cmp(&a.1));
+        let fees = compute_recommended_fees(&block_stats);

-        // Build blocks greedily
-        let mut blocks = Vec::with_capacity(NUM_PROJECTED_BLOCKS);
-        let mut current_block = ProjectedBlock::default();
-        let mut included: FxHashSet<Txid> = FxHashSet::default();
+        // Convert to just indices for storage
+        let blocks: Vec<Vec<MempoolTxIndex>> = blocks
+            .into_iter()
+            .map(|selected| selected.into_iter().map(|s| s.entries_idx).collect())
+            .collect();

-        for (txid, fee_rate, vsize, fee) in sorted {
-            // Skip if already included (as part of ancestor package)
-            if included.contains(&txid) {
-                continue;
-            }
-
-            // Would this tx fit in the current block?
-            let new_vsize = current_block.total_vsize + vsize;
-
-            if u64::from(new_vsize) > BLOCK_VSIZE_TARGET && !current_block.txids.is_empty() {
-                // Finalize and store current block
-                Self::finalize_block(&mut current_block);
-                blocks.push(mem::take(&mut current_block));
-
-                if blocks.len() >= NUM_PROJECTED_BLOCKS {
-                    break;
-                }
-            }
-
-            // Add to current block
-            current_block.txids.push(txid.clone());
-            current_block.total_vsize += vsize;
-            current_block.total_fee += fee;
-            included.insert(txid);
-
-            // Track fee rate bounds
-            if current_block.max_fee_rate == FeeRate::default() {
-                current_block.max_fee_rate = fee_rate;
-            }
-            current_block.min_fee_rate = fee_rate;
+        Self {
+            blocks,
+            block_stats,
+            fees,
        }
-
-        // Don't forget the last block
-        if !current_block.txids.is_empty() && blocks.len() < NUM_PROJECTED_BLOCKS {
-            Self::finalize_block(&mut current_block);
-            blocks.push(current_block);
-        }
-
-        Self { blocks }
-    }
-
-    /// Compute recommended fees from projected blocks
-    pub fn recommended_fees(&self) -> RecommendedFees {
-        RecommendedFees {
-            fastest_fee: self.fee_for_block(0),
-            half_hour_fee: self.fee_for_block(2), // ~3 blocks
-            hour_fee: self.fee_for_block(5),      // ~6 blocks
-            economy_fee: self.fee_for_block(7),   // ~8 blocks
-            minimum_fee: FeeRate::from(MIN_FEE_RATE),
-        }
-    }
-
-    /// Get the minimum fee rate needed to get into block N
-    fn fee_for_block(&self, block_index: usize) -> FeeRate {
-        self.blocks
-            .get(block_index)
-            .map(|b| b.min_fee_rate)
-            .unwrap_or_else(|| FeeRate::from(MIN_FEE_RATE))
-    }
-
-    fn finalize_block(block: &mut ProjectedBlock) {
-        // Compute median fee rate from min/max as approximation
-        // (true median would require storing all fee rates)
-        let min = f64::from(block.min_fee_rate);
-        let max = f64::from(block.max_fee_rate);
-        block.median_fee_rate = FeeRate::from((min + max) / 2.0);
    }
 }
+
+/// Compute statistics for a single block using effective fee rates from selection time.
+fn compute_block_stats(selected: &[SelectedTx], entries: &[Option<MempoolEntry>]) -> BlockStats {
+    if selected.is_empty() {
+        return BlockStats::default();
+    }
+
+    let mut total_fee = Sats::default();
+    let mut total_vsize = VSize::default();
+    let mut fee_rates: Vec<FeeRate> = Vec::with_capacity(selected.len());
+
+    for sel in selected {
+        if let Some(entry) = &entries[sel.entries_idx.as_usize()] {
+            total_fee += entry.fee;
+            total_vsize += entry.vsize;
+            // Use the effective fee rate captured at selection time
+            // This is the actual mining score that determined this tx's block placement
+            fee_rates.push(sel.effective_fee_rate);
+        }
+    }
+
+    fee_rates.sort();
+
+    BlockStats {
+        tx_count: selected.len() as u32,
+        total_vsize,
+        total_fee,
+        fee_range: [
+            percentile(&fee_rates, 0),
+            percentile(&fee_rates, 10),
+            percentile(&fee_rates, 25),
+            percentile(&fee_rates, 50),
+            percentile(&fee_rates, 75),
+            percentile(&fee_rates, 90),
+            percentile(&fee_rates, 100),
+        ],
+    }
+}
+
+/// Get percentile value from sorted array.
+fn percentile(sorted: &[FeeRate], p: usize) -> FeeRate {
+    if sorted.is_empty() {
+        return FeeRate::default();
+    }
+    let idx = (p * (sorted.len() - 1)) / 100;
+    sorted[idx]
+}
+
+/// Compute recommended fees from block stats (mempool.space style).
+fn compute_recommended_fees(stats: &[BlockStats]) -> RecommendedFees {
+    RecommendedFees {
+        // High priority: median of block 1
+        fastest_fee: median_fee_for_block(stats, 0),
+        // Medium priority: median of blocks 2-3
+        half_hour_fee: median_fee_for_block(stats, 2),
+        // Low priority: median of blocks 4-6
+        hour_fee: median_fee_for_block(stats, 5),
+        // No priority: median of later blocks
+        economy_fee: median_fee_for_block(stats, 7),
+        minimum_fee: FeeRate::from(MIN_FEE_RATE),
+    }
+}
+
+/// Get the median fee rate for block N.
+fn median_fee_for_block(stats: &[BlockStats], block_index: usize) -> FeeRate {
+    stats
+        .get(block_index)
+        .map(|s| s.median_fee_rate())
+        .unwrap_or_else(|| FeeRate::from(MIN_FEE_RATE))
+}
@@ -0,0 +1,47 @@
+/// Index into the mempool entries Vec.
+/// NOT the global TxIndex for confirmed transactions.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct MempoolTxIndex(pub(crate) u32);
+
+impl MempoolTxIndex {
+    #[inline]
+    pub fn as_usize(self) -> usize {
+        self.0 as usize
+    }
+}
+
+impl From<usize> for MempoolTxIndex {
+    #[inline]
+    fn from(value: usize) -> Self {
+        Self(value as u32)
+    }
+}
+
+/// Index into the temporary pool Vec used during block building.
+/// Distinct from MempoolTxIndex to prevent mixing up index spaces.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct PoolIndex(u32);
+
+impl PoolIndex {
+    #[inline]
+    pub fn as_usize(self) -> usize {
+        self.0 as usize
+    }
+}
+
+impl From<usize> for PoolIndex {
+    #[inline]
+    fn from(value: usize) -> Self {
+        Self(value as u32)
+    }
+}
+
+/// A selected transaction with its effective mining score at selection time.
+/// The effective_fee_rate is the ancestor score when this tx was selected,
+/// which may differ from the original ancestor score (if ancestors were already mined).
+#[derive(Debug, Clone, Copy)]
+pub struct SelectedTx {
+    pub entries_idx: MempoolTxIndex,
+    /// Fee rate at selection time (ancestor_fee / ancestor_vsize)
+    pub effective_fee_rate: brk_types::FeeRate,
+}
@@ -9,7 +9,10 @@ use bitcoincore_rpc::{
    {Client as CoreClient, Error as RpcError, RpcApi},
 };
 use brk_error::Result;
-use brk_types::{BlockHash, Height, Sats, Transaction, TxIn, TxOut, TxStatus, TxWithHex, Txid, Vout};
+use brk_types::{
+    BlockHash, Height, MempoolEntryInfo, Sats, Transaction, TxIn, TxOut, TxStatus, TxWithHex, Txid,
+    Vout,
+};

 pub use bitcoincore_rpc::Auth;

@@ -196,6 +199,24 @@ impl Client {
            .map_err(Into::into)
    }

+    /// Get all mempool entries with their fee data in a single RPC call
+    pub fn get_raw_mempool_verbose(&self) -> Result<Vec<MempoolEntryInfo>> {
+        let result = self.call(|c| c.get_raw_mempool_verbose())?;
+        Ok(result
+            .into_iter()
+            .map(|(txid, entry)| MempoolEntryInfo {
+                txid: txid.into(),
+                vsize: entry.vsize,
+                weight: entry.weight.unwrap_or(entry.vsize * 4),
+                fee: Sats::from(entry.fees.base.to_sat()),
+                ancestor_count: entry.ancestor_count,
+                ancestor_size: entry.ancestor_size,
+                ancestor_fee: Sats::from(entry.fees.ancestor.to_sat()),
+                depends: entry.depends.into_iter().map(Txid::from).collect(),
+            })
+            .collect())
+    }
+
    pub fn get_raw_transaction<'a, T, H>(
        &self,
        txid: &'a T,
@@ -43,6 +43,7 @@ mod limit;
 mod loadedaddressdata;
 mod loadedaddressindex;
 mod metric;
+mod mempoolentryinfo;
 mod mempoolinfo;
 mod metriccount;
 mod metrics;
@@ -151,6 +152,7 @@ pub use indexinfo::*;
 pub use limit::*;
 pub use loadedaddressdata::*;
 pub use loadedaddressindex::*;
+pub use mempoolentryinfo::*;
 pub use mempoolinfo::*;
 pub use metric::*;
 pub use metriccount::*;
@@ -0,0 +1,15 @@
+use crate::{Sats, Txid};
+
+/// Mempool entry info from Bitcoin Core's getrawmempool verbose
+#[derive(Debug, Clone)]
+pub struct MempoolEntryInfo {
+    pub txid: Txid,
+    pub vsize: u64,
+    pub weight: u64,
+    pub fee: Sats,
+    pub ancestor_count: u64,
+    pub ancestor_size: u64,
+    pub ancestor_fee: Sats,
+    /// Parent txids in the mempool
+    pub depends: Vec<Txid>,
+}
@@ -0,0 +1,133 @@
+# Mempool.space API Compatibility - Implementation Status
+
+Plan file: `/Users/k/.claude/plans/smooth-weaving-crayon.md`
+
+## Completed Endpoints
+
+| Endpoint | Path | Notes |
+|----------|------|-------|
+| GET Block | `/api/block/{hash}` | |
+| GET Block Height | `/api/block-height/{height}` | Returns plain text hash |
+| GET Block Status | `/api/block/{hash}/status` | |
+| GET Block Txids | `/api/block/{hash}/txids` | |
+| GET Blocks | `/api/blocks[/:start_height]` | Last 10 blocks |
+| GET Transaction | `/api/tx/{txid}` | |
+| GET Tx Status | `/api/tx/{txid}/status` | |
+| GET Tx Hex | `/api/tx/{txid}/hex` | Returns plain text |
+| GET Address | `/api/address/{address}` | |
+| GET Address Txs | `/api/address/{address}/txs` | |
+| GET Address UTXOs | `/api/address/{address}/utxo` | |
+| GET Mempool Info | `/api/mempool/info` | |
+| GET Mempool Txids | `/api/mempool/txids` | |
+| GET Recommended Fees | `/api/v1/fees/recommended` | Basic impl, needs optimization |
+
+## Remaining Endpoints
+
+### Mempool/Fees (4)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 1 | Optimize projected blocks | - | CPFP/ancestor scores | HIGH |
+| 2 | GET Mempool Blocks | `/api/v1/fees/mempool-blocks` | #1 | HIGH |
+| 3 | GET Mempool Recent | `/api/mempool/recent` | | MED |
+| 4 | GET RBF Replacements | `/api/v1/replacements` | RBF tracking in brk_monitor | LOW |
+
+### Blocks (4)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 5 | GET Block Txs | `/api/block/{hash}/txs[/:start_index]` | | MED |
+| 6 | GET Block Txid at Index | `/api/block/{hash}/txid/{index}` | | LOW |
+| 7 | GET Block Raw | `/api/block/{hash}/raw` | brk_reader | LOW |
+| 8 | GET Block by Timestamp | `/api/v1/mining/blocks/timestamp/{timestamp}` | Binary search | LOW |
+
+### Addresses (3)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 9 | GET Address Txs Chain | `/api/address/{address}/txs/chain[/:after_txid]` | | MED |
+| 10 | GET Address Txs Mempool | `/api/address/{address}/txs/mempool` | brk_monitor | MED |
+| 11 | GET Validate Address | `/api/v1/validate-address/{address}` | | LOW |
+
+### Transactions (4)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 12 | GET Tx Outspend | `/api/tx/{txid}/outspend/{vout}` | #27 txoutindex_to_txinindex | HIGH |
+| 13 | GET Tx Outspends | `/api/tx/{txid}/outspends` | #27 | HIGH |
+| 14 | GET Tx Merkle Proof | `/api/tx/{txid}/merkle-proof` | | LOW |
+| 15 | POST Tx Broadcast | `/api/tx` | brk_rpc | MED |
+
+### General (1)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 16 | GET Difficulty Adjustment | `/api/v1/difficulty-adjustment` | | MED |
+
+### Mining (9)
+
+| # | Endpoint | Path | Dependencies | Priority |
+|---|----------|------|--------------|----------|
+| 17 | GET Mining Pools | `/api/v1/mining/pools[/:timePeriod]` | #28 pool identification | LOW |
+| 18 | GET Mining Pool | `/api/v1/mining/pool/{slug}` | #28 | LOW |
+| 19 | GET Hashrate | `/api/v1/mining/hashrate[/:timePeriod]` | | MED |
+| 20 | GET Difficulty Adjustments | `/api/v1/mining/difficulty-adjustments[/:interval]` | | LOW |
+| 21 | GET Reward Stats | `/api/v1/mining/reward-stats/{blockCount}` | | LOW |
+| 22 | GET Block Fees | `/api/v1/mining/blocks/fees/{timePeriod}` | | LOW |
+| 23 | GET Block Rewards | `/api/v1/mining/blocks/rewards/{timePeriod}` | | LOW |
+| 24 | GET Block Fee Rates | `/api/v1/mining/blocks/fee-rates/{timePeriod}` | | LOW |
+| 25 | GET Block Sizes/Weights | `/api/v1/mining/blocks/sizes-weights/{timePeriod}` | | LOW |
+
+### Infrastructure (3)
+
+| # | Task | Location | Priority |
+|---|------|----------|----------|
+| 26 | Index txindex_to_sigop_cost | brk_indexer | MED |
+| 27 | Add txoutindex_to_txinindex mapping | brk_computer/stateful | HIGH |
+| 28 | Pool identification from coinbase | brk_computer | LOW |
+
+## Priority Order
+
+### Phase 1: Core Functionality (HIGH)
+1. **#27** Add txoutindex_to_txinindex mapping (enables outspend lookups)
+2. **#12** GET Tx Outspend
+3. **#13** GET Tx Outspends
+4. **#1** Optimize projected blocks (CPFP/ancestor scores)
+5. **#2** GET Mempool Blocks
+
+### Phase 2: Essential Features (MED)
+6. **#15** POST Tx Broadcast
+7. **#16** GET Difficulty Adjustment
+8. **#5** GET Block Txs (paginated)
+9. **#9** GET Address Txs Chain
+10. **#10** GET Address Txs Mempool
+11. **#19** GET Hashrate
+12. **#26** Index txindex_to_sigop_cost
+13. **#3** GET Mempool Recent
+
+### Phase 3: Nice to Have (LOW)
+14. **#6** GET Block Txid at Index
+15. **#7** GET Block Raw
+16. **#8** GET Block by Timestamp
+17. **#11** GET Validate Address
+18. **#14** GET Tx Merkle Proof
+19. **#4** GET RBF Replacements
+20. **#20** GET Difficulty Adjustments
+21. **#21** GET Reward Stats
+22. **#22-25** Mining block statistics
+23. **#17-18** Mining pools (requires #28)
+24. **#28** Pool identification
+
+## Design Documents
+
+- Mempool projected blocks: `crates/brk_monitor/src/mempool/DESIGN.md`
+
+## Skipped Endpoints
+
+| Endpoint | Reason |
+|----------|--------|
+| GET Price | `/api/v1/prices` | External data source needed |
+| GET Historical Price | `/api/v1/historical-price` | External data source needed |
+| GET Full-RBF Replacements | `/api/v1/fullrbf/replacements` | Low priority |
+| Lightning endpoints | Requires separate Lightning indexing |
+| Accelerator endpoints | mempool.space-specific paid service |