From 92bca485b62df90396f359da001403e16c2c584f Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Fri, 10 Mar 2023 12:59:23 -0800
Subject: [PATCH] feat: stmgr: skip tipset execution when possible

---
 chain/stmgr/execute.go | 52 ++++++++++++++++++++++++++++++++++++++++++
 chain/types/tipset.go  |  4 ++++
 2 files changed, 56 insertions(+)

diff --git a/chain/stmgr/execute.go b/chain/stmgr/execute.go
index e673982992a..57ff205b91f 100644
--- a/chain/stmgr/execute.go
+++ b/chain/stmgr/execute.go
@@ -8,6 +8,7 @@ import (
 	"go.opencensus.io/trace"
 
 	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/chain/store"
 	"github.com/filecoin-project/lotus/chain/types"
 )
 
@@ -52,6 +53,12 @@ func (sm *StateManager) TipSetState(ctx context.Context, ts *types.TipSet) (st c
 
 	sm.stlk.Unlock()
 
+	// First, try to find the tipset in the current chain. If found, we can avoid re-executing
+	// it.
+	if st, rec, found := tryLookupTipsetState(ctx, sm.cs, ts); found {
+		return st, rec, nil
+	}
+
 	st, rec, err = sm.tsExec.ExecuteTipSet(ctx, sm, ts, sm.tsExecMonitor, false)
 	if err != nil {
 		return cid.Undef, cid.Undef, err
@@ -60,6 +67,51 @@ func (sm *StateManager) TipSetState(ctx context.Context, ts *types.TipSet) (st c
 	return st, rec, nil
 }
 
+// Try to lookup a state & receipt CID for a given tipset by walking the chain instead of executing
+// it. This will only successfully return the state/receipt CIDs if they're found in the state
+// store.
+//
+// NOTE: This _won't_ recursively walk the receipt/state trees. It assumes that having the root
+// implies having the rest of the tree. However, lotus generally makes that assumption anyways.
+func tryLookupTipsetState(ctx context.Context, cs *store.ChainStore, ts *types.TipSet) (cid.Cid, cid.Cid, bool) {
+	nextTs, err := cs.GetTipsetByHeight(ctx, ts.Height()+1, nil, false)
+	if err != nil {
+		// Nothing to see here. The requested height may be beyond the current head.
+		return cid.Undef, cid.Undef, false
+	}
+
+	// Make sure we're on the correct fork.
+	if nextTs.Parents() != ts.Key() {
+		// Also nothing to see here. This just means that the requested tipset is on a
+		// different fork.
+		return cid.Undef, cid.Undef, false
+	}
+
+	stateCid := nextTs.ParentState()
+	receiptCid := nextTs.ParentMessageReceipts()
+
+	// Make sure we have the parent state.
+	if hasState, err := cs.StateBlockstore().Has(ctx, stateCid); err != nil {
+		log.Errorw("failed to lookup state-root in blockstore", "cid", stateCid, "error", err)
+		return cid.Undef, cid.Undef, false
+	} else if !hasState {
+		// We have the chain but don't have the state. It looks like we need to try
+		// executing?
+		return cid.Undef, cid.Undef, false
+	}
+
+	// Make sure we have the receipts.
+	if hasReceipts, err := cs.ChainBlockstore().Has(ctx, receiptCid); err != nil {
+		log.Errorw("failed to lookup receipts in blockstore", "cid", receiptCid, "error", err)
+		return cid.Undef, cid.Undef, false
+	} else if !hasReceipts {
+		// If we don't have the receipts, re-execute and try again.
+		return cid.Undef, cid.Undef, false
+	}
+
+	return stateCid, receiptCid, true
+}
+
 func (sm *StateManager) ExecutionTraceWithMonitor(ctx context.Context, ts *types.TipSet, em ExecMonitor) (cid.Cid, error) {
 	st, _, err := sm.tsExec.ExecuteTipSet(ctx, sm, ts, em, true)
 	return st, err
diff --git a/chain/types/tipset.go b/chain/types/tipset.go
index c1aa90fc9da..047a1c00e09 100644
--- a/chain/types/tipset.go
+++ b/chain/types/tipset.go
@@ -234,6 +234,10 @@ func (ts *TipSet) MinTicketBlock() *BlockHeader {
 	return min
 }
 
+func (ts *TipSet) ParentMessageReceipts() cid.Cid {
+	return ts.blks[0].ParentMessageReceipts
+}
+
 func (ts *TipSet) ParentState() cid.Cid {
 	return ts.blks[0].ParentStateRoot
 }