New building algorithm. (#214)

## 📝 Summary

New experimental BlockBuildingAlgorithm added!

## 💡 Motivation and Context

The other algorithm was quite lonely and sad.

## ✅ I have completed the following steps:

* [X] Run `make lint`
* [X] Run `make test`
* [ ] Added tests (if applicable)

config-backtest-example.toml

@@ -28,3 +28,9 @@ sorting = "max-profit"
 failed_order_retries = 1
 drop_failed_orders = true
 
+[[builders]]
+name = "merging"
+algo = "merging-builder"
+discard_txs = true
+num_threads = 5
+merge_wait_time_ms = 100

config-live-example.toml

@@ -58,3 +58,10 @@ discard_txs = true
 sorting = "max-profit"
 failed_order_retries = 1
 drop_failed_orders = true
+
+[[builders]]
+name = "merging"
+algo = "merging-builder"
+discard_txs = true
+num_threads = 5
+merge_wait_time_ms = 100

crates/rbuilder/src/building/builders/merging_builder/combinator.rs

@@ -0,0 +1,170 @@
+use crate::{
+    building::{
+        builders::block_building_helper::{BlockBuildingHelper, BlockBuildingHelperFromDB},
+        BlockBuildingContext,
+    },
+    roothash::RootHashConfig,
+};
+
+use crate::utils::check_provider_factory_health;
+use reth::{providers::ProviderFactory, tasks::pool::BlockingTaskPool};
+use reth_db::database::Database;
+use reth_payload_builder::database::CachedReads;
+use std::time::Instant;
+use time::OffsetDateTime;
+use tokio_util::sync::CancellationToken;
+use tracing::{info_span, trace};
+
+use super::{GroupOrdering, OrderGroup};
+
+/// CombinatorContext is used for merging the best ordering from groups into final block.
+#[derive(Debug)]
+pub struct CombinatorContext<DB> {
+    provider_factory: ProviderFactory<DB>,
+    root_hash_task_pool: BlockingTaskPool,
+    ctx: BlockBuildingContext,
+    groups: Vec<OrderGroup>,
+    cancellation_token: CancellationToken,
+    cached_reads: Option<CachedReads>,
+    discard_txs: bool,
+    coinbase_payment: bool,
+    root_hash_config: RootHashConfig,
+    builder_name: String,
+}
+
+impl<DB: Database + Clone + 'static> CombinatorContext<DB> {
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(
+        provider_factory: ProviderFactory<DB>,
+        root_hash_task_pool: BlockingTaskPool,
+        ctx: BlockBuildingContext,
+        groups: Vec<OrderGroup>,
+        cancellation_token: CancellationToken,
+        cached_reads: Option<CachedReads>,
+        discard_txs: bool,
+        coinbase_payment: bool,
+        root_hash_config: RootHashConfig,
+        builder_name: String,
+    ) -> Self {
+        CombinatorContext {
+            provider_factory,
+            root_hash_task_pool,
+            ctx,
+            groups,
+            cancellation_token,
+            cached_reads,
+            discard_txs,
+            coinbase_payment,
+            root_hash_config,
+            builder_name,
+        }
+    }
+
+    pub fn set_groups(&mut self, groups: Vec<OrderGroup>) {
+        self.groups = groups;
+    }
+
+    /// Checks for simulated bundles that generated kickbacks.
+    /// orderings MUST be the same size as self.groups
+    fn contains_kickbacks(&self, orderings: &[GroupOrdering]) -> bool {
+        orderings.iter().enumerate().any(|(group_idx, ordering)| {
+            ordering.orders.iter().any(|(order_idx, _)| {
+                !self.groups[group_idx].orders[*order_idx]
+                    .sim_value
+                    .paid_kickbacks
+                    .is_empty()
+            })
+        })
+    }
+
+    pub fn combine_best_groups_mergings(
+        &mut self,
+        orders_closed_at: OffsetDateTime,
+        can_use_suggested_fee_recipient_as_coinbase: bool,
+    ) -> eyre::Result<Box<dyn BlockBuildingHelper>> {
+        let build_attempt_id: u32 = rand::random();
+        let span = info_span!("build_run", build_attempt_id);
+        let _guard = span.enter();
+        check_provider_factory_health(self.ctx.block(), &self.provider_factory)?;
+
+        let build_start = Instant::now();
+
+        let mut best_orderings: Vec<GroupOrdering> = self
+            .groups
+            .iter()
+            .map(|g| g.best_ordering.lock().unwrap().clone())
+            .collect();
+
+        let use_suggested_fee_recipient_as_coinbase = self.coinbase_payment
+            && !self.contains_kickbacks(&best_orderings)
+            && can_use_suggested_fee_recipient_as_coinbase;
+        // Create a new ctx to remove builder_signer if necessary
+        let mut ctx = self.ctx.clone();
+        if use_suggested_fee_recipient_as_coinbase {
+            ctx.modify_use_suggested_fee_recipient_as_coinbase();
+        }
+
+        let mut block_building_helper = BlockBuildingHelperFromDB::new(
+            self.provider_factory.clone(),
+            self.root_hash_task_pool.clone(),
+            self.root_hash_config.clone(),
+            ctx,
+            // @Perf cached reads / cursor caches
+            None,
+            self.builder_name.clone(),
+            self.discard_txs,
+            None,
+            self.cancellation_token.clone(),
+        )?;
+        block_building_helper.set_trace_orders_closed_at(orders_closed_at);
+        // loop until we insert all orders into the block
+        loop {
+            if self.cancellation_token.is_cancelled() {
+                break;
+            }
+
+            let sim_order = if let Some((group_idx, order_idx, _)) = best_orderings
+                .iter()
+                .enumerate()
+                .filter_map(|(group_idx, ordering)| {
+                    ordering
+                        .orders
+                        .first()
+                        .map(|(order_idx, order_profit)| (group_idx, *order_idx, *order_profit))
+                })
+                .max_by_key(|(_, _, p)| *p)
+            {
+                best_orderings[group_idx].orders.remove(0);
+                &self.groups[group_idx].orders[order_idx]
+            } else {
+                // no order left in the groups
+                break;
+            };
+
+            let start_time = Instant::now();
+            let commit_result = block_building_helper.commit_order(sim_order)?;
+            let order_commit_time = start_time.elapsed();
+
+            let mut gas_used = 0;
+            let mut execution_error = None;
+            let success = commit_result.is_ok();
+            match commit_result {
+                Ok(res) => {
+                    gas_used = res.gas_used;
+                }
+                Err(err) => execution_error = Some(err),
+            }
+            trace!(
+                order_id = ?sim_order.id(),
+                success,
+                order_commit_time_mus = order_commit_time.as_micros(),
+                gas_used,
+                ?execution_error,
+                "Executed order"
+            );
+        }
+        block_building_helper.set_trace_fill_time(build_start.elapsed());
+        self.cached_reads = Some(block_building_helper.clone_cached_reads());
+        Ok(Box::new(block_building_helper))
+    }
+}