From 678fb674ebc23888c7dfd1d4b22110be2e0522e5 Mon Sep 17 00:00:00 2001
From: nsa <elzeigel@gmail.com>
Date: Thu, 27 Jun 2019 13:34:55 -0400
Subject: [PATCH] routing: move call to PruneGraph outside of the collating
 loop

This commit moves the call to PruneGraph outside of the loop
that collates all of the spentOutputs. With this change, if
a node has been offline for a long period of time, resyncing
with the chain no longer takes up as much memory (1MB vs 200MB
in some cases) or time. Previously, PruneGraph was called
for every block and allocated a very large map further down
in the pruneGraphNodes function. Now, pruneGraphNodes is only
called once.
---
 routing/router.go | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/routing/router.go b/routing/router.go
index 388f5ba0..972be896 100644
--- a/routing/router.go
+++ b/routing/router.go
@@ -680,7 +680,7 @@ func (r *ChannelRouter) syncGraphWithChain() error {
 	// If we're not yet caught up, then we'll walk forward in the chain
 	// pruning the channel graph with each new block that hasn't yet been
 	// consumed by the channel graph.
-	var numChansClosed uint32
+	var spentOutputs []*wire.OutPoint
 	for nextHeight := pruneHeight + 1; nextHeight <= uint32(bestHeight); nextHeight++ {
 		// Break out of the rescan early if a shutdown has been
 		// requested, otherwise long rescans will block the daemon from
@@ -705,33 +705,25 @@ func (r *ChannelRouter) syncGraphWithChain() error {
 		// We're only interested in all prior outputs that have been
 		// spent in the block, so collate all the referenced previous
 		// outpoints within each tx and input.
-		var spentOutputs []*wire.OutPoint
 		for _, tx := range filterBlock.Transactions {
 			for _, txIn := range tx.TxIn {
 				spentOutputs = append(spentOutputs,
 					&txIn.PreviousOutPoint)
 			}
 		}
+	}
 
-		// With the spent outputs gathered, attempt to prune the
-		// channel graph, also passing in the hash+height of the block
-		// being pruned so the prune tip can be updated.
-		closedChans, err := r.cfg.Graph.PruneGraph(spentOutputs,
-			nextHash,
-			nextHeight)
-		if err != nil {
-			return err
-		}
-
-		numClosed := uint32(len(closedChans))
-		log.Infof("Block %v (height=%v) closed %v channels",
-			nextHash, nextHeight, numClosed)
-
-		numChansClosed += numClosed
+	// With the spent outputs gathered, attempt to prune the channel graph,
+	// also passing in the best hash+height so the prune tip can be updated.
+	closedChans, err := r.cfg.Graph.PruneGraph(
+		spentOutputs, bestHash, uint32(bestHeight),
+	)
+	if err != nil {
+		return err
 	}
 
 	log.Infof("Graph pruning complete: %v channels were closed since "+
-		"height %v", numChansClosed, pruneHeight)
+		"height %v", len(closedChans), pruneHeight)
 	return nil
 }