From f4e466955d0e67a48f55ddae324069b2c48415e4 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Thu, 3 Mar 2022 14:38:03 +0200
Subject: [PATCH] lib/mergeset: move storageBlock from inmemoryPart to a
 sync.Pool

The lifetime of storageBlock is much shorter comparing to the lifetime of inmemoryPart,
so sync.Pool usage should reduce overall memory usage and improve performance
because of better locality of reference when marshaling inmemoryBlock to inmemoryPart.

https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2247
---
 lib/mergeset/encoding.go      | 15 +++++++++++++++
 lib/mergeset/inmemory_part.go | 14 +++++++-------
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/lib/mergeset/encoding.go b/lib/mergeset/encoding.go
index b7774d720..7dd6dd3f9 100644
--- a/lib/mergeset/encoding.go
+++ b/lib/mergeset/encoding.go
@@ -148,6 +148,21 @@ func (sb *storageBlock) Reset() {
 	sb.lensData = sb.lensData[:0]
 }
 
+func getStorageBlock() *storageBlock {
+	v := storageBlockPool.Get()
+	if v == nil {
+		return &storageBlock{}
+	}
+	return v.(*storageBlock)
+}
+
+func putStorageBlock(sb *storageBlock) {
+	sb.Reset()
+	storageBlockPool.Put(sb)
+}
+
+var storageBlockPool sync.Pool
+
 type marshalType uint8
 
 const (
diff --git a/lib/mergeset/inmemory_part.go b/lib/mergeset/inmemory_part.go
index 9b556fd0e..3816fee24 100644
--- a/lib/mergeset/inmemory_part.go
+++ b/lib/mergeset/inmemory_part.go
@@ -10,7 +10,6 @@ import (
 
 type inmemoryPart struct {
 	ph partHeader
-	sb storageBlock
 	bh blockHeader
 	mr metaindexRow
 
@@ -28,7 +27,6 @@ type inmemoryPart struct {
 
 func (mp *inmemoryPart) Reset() {
 	mp.ph.Reset()
-	mp.sb.Reset()
 	mp.bh.Reset()
 	mp.mr.Reset()
 
@@ -47,25 +45,27 @@ func (mp *inmemoryPart) Reset() {
 // Init initializes mp from ib.
 func (mp *inmemoryPart) Init(ib *inmemoryBlock) {
 	mp.Reset()
+	sb := getStorageBlock()
+	defer putStorageBlock(sb)
 
 	// Use the minimum possible compressLevel for compressing inmemoryPart,
 	// since it will be merged into file part soon.
 	// See https://github.com/facebook/zstd/releases/tag/v1.3.4 for details about negative compression level
 	compressLevel := -5
-	mp.bh.firstItem, mp.bh.commonPrefix, mp.bh.itemsCount, mp.bh.marshalType = ib.MarshalUnsortedData(&mp.sb, mp.bh.firstItem[:0], mp.bh.commonPrefix[:0], compressLevel)
+	mp.bh.firstItem, mp.bh.commonPrefix, mp.bh.itemsCount, mp.bh.marshalType = ib.MarshalUnsortedData(sb, mp.bh.firstItem[:0], mp.bh.commonPrefix[:0], compressLevel)
 
 	mp.ph.itemsCount = uint64(len(ib.items))
 	mp.ph.blocksCount = 1
 	mp.ph.firstItem = append(mp.ph.firstItem[:0], ib.items[0].String(ib.data)...)
 	mp.ph.lastItem = append(mp.ph.lastItem[:0], ib.items[len(ib.items)-1].String(ib.data)...)
 
-	fs.MustWriteData(&mp.itemsData, mp.sb.itemsData)
+	fs.MustWriteData(&mp.itemsData, sb.itemsData)
 	mp.bh.itemsBlockOffset = 0
-	mp.bh.itemsBlockSize = uint32(len(mp.sb.itemsData))
+	mp.bh.itemsBlockSize = uint32(len(mp.itemsData.B))
 
-	fs.MustWriteData(&mp.lensData, mp.sb.lensData)
+	fs.MustWriteData(&mp.lensData, sb.lensData)
 	mp.bh.lensBlockOffset = 0
-	mp.bh.lensBlockSize = uint32(len(mp.sb.lensData))
+	mp.bh.lensBlockSize = uint32(len(mp.lensData.B))
 
 	mp.unpackedIndexBlockBuf = mp.bh.Marshal(mp.unpackedIndexBlockBuf[:0])
 	mp.packedIndexBlockBuf = encoding.CompressZSTDLevel(mp.packedIndexBlockBuf[:0], mp.unpackedIndexBlockBuf, 0)