From 07595564afa6201d8858a06d47ea9c26023307de Mon Sep 17 00:00:00 2001
From: guo-shaoge <shaoge1994@163.com>
Date: Tue, 18 May 2021 14:59:05 +0800
Subject: [PATCH] Revert "add isReaderStale"

This reverts commit c45b41dae7eab88cbf4edbdb433e3ef4214bd3c6.
---
 util/chunk/disk.go      | 19 +++++--------------
 util/chunk/disk_test.go | 30 ------------------------------
 2 files changed, 5 insertions(+), 44 deletions(-)

diff --git a/util/chunk/disk.go b/util/chunk/disk.go
index f0d16dc037157..ef269213e9d0d 100644
--- a/util/chunk/disk.go
+++ b/util/chunk/disk.go
@@ -49,10 +49,6 @@ type ListInDisk struct {
 	checksumWriter *checksum.Writer
 	cipherWriter   *encrypt.Writer
 
-	// By using this flag, we don't need to allocate a new reader every time.
-	isReaderStale bool
-	r             io.ReaderAt
-
 	// ctrCipher stores the key and nonce using by aes encrypt io layer
 	ctrCipher *encrypt.CtrCipher
 }
@@ -64,8 +60,7 @@ func NewListInDisk(fieldTypes []*types.FieldType) *ListInDisk {
 	l := &ListInDisk{
 		fieldTypes: fieldTypes,
 		// TODO(fengliyuan): set the quota of disk usage.
-		diskTracker:   disk.NewTracker(memory.LabelForChunkListInDisk, -1),
-		isReaderStale: true,
+		diskTracker: disk.NewTracker(memory.LabelForChunkListInDisk, -1),
 	}
 	return l
 }
@@ -155,7 +150,6 @@ func (l *ListInDisk) Add(chk *Chunk) (err error) {
 	l.offsets = append(l.offsets, chk2.getOffsetsOfRows())
 	l.diskTracker.Consume(n)
 	l.numRowsInDisk += chk.NumRows()
-	l.isReaderStale = true
 	return
 }
 
@@ -180,14 +174,11 @@ func (l *ListInDisk) GetRow(ptr RowPtr) (row Row, err error) {
 	}
 	off := l.offsets[ptr.ChkIdx][ptr.RowIdx]
 	var underlying io.ReaderAt = l.disk
-	if l.isReaderStale {
-		if l.ctrCipher != nil {
-			underlying = NewReaderWithCache(encrypt.NewReader(l.disk, l.ctrCipher), l.cipherWriter.GetCache(), l.cipherWriter.GetCacheDataOffset())
-		}
-		l.r = NewReaderWithCache(checksum.NewReader(underlying), l.checksumWriter.GetCache(), l.checksumWriter.GetCacheDataOffset())
-		l.isReaderStale = false
+	if l.ctrCipher != nil {
+		underlying = NewReaderWithCache(encrypt.NewReader(l.disk, l.ctrCipher), l.cipherWriter.GetCache(), l.cipherWriter.GetCacheDataOffset())
 	}
-	r := io.NewSectionReader(l.r, off, l.offWrite-off)
+	checksumReader := NewReaderWithCache(checksum.NewReader(underlying), l.checksumWriter.GetCache(), l.checksumWriter.GetCacheDataOffset())
+	r := io.NewSectionReader(checksumReader, off, l.offWrite-off)
 	format := rowInDisk{numCol: len(l.fieldTypes)}
 	_, err = format.ReadFrom(r)
 	if err != nil {
diff --git a/util/chunk/disk_test.go b/util/chunk/disk_test.go
index c534f6c49b009..36750aa898244 100644
--- a/util/chunk/disk_test.go
+++ b/util/chunk/disk_test.go
@@ -263,7 +263,6 @@ func testReaderWithCache(c *check.C) {
 	chk := NewChunkWithCapacity(field, 1)
 	chk.AppendString(0, buf.String())
 	l := NewListInDisk(field)
-	c.Assert(l.isReaderStale, check.IsTrue)
 	err := l.Add(chk)
 	c.Assert(err, check.IsNil)
 
@@ -328,35 +327,6 @@ func testReaderWithCache(c *check.C) {
 	c.Assert(err, check.IsNil)
 	c.Assert(readCnt, check.Equals, 10)
 	c.Assert(reflect.DeepEqual(data, buf.Bytes()[1002:1012]), check.IsTrue)
-
-	// Test l.isReaderStale works properly
-	// It means only new reader is alloced after writing.
-	oriReader := l.r
-	for i := 0; i < 100; i++ {
-		row, err = l.GetRow(RowPtr{0, 0})
-		c.Assert(err, check.IsNil)
-		c.Assert(oriReader == l.r, check.IsTrue)
-		c.Assert(l.isReaderStale, check.IsFalse)
-	}
-	// After write, reader is stale.
-	err = l.Add(chk)
-	c.Assert(err, check.IsNil)
-	c.Assert(oriReader == l.r, check.IsTrue)
-	c.Assert(l.isReaderStale, check.IsTrue)
-
-	// New reader is generated when reading.
-	row, err = l.GetRow(RowPtr{1, 0})
-	c.Assert(err, check.IsNil)
-	c.Assert(oriReader != l.r, check.IsTrue)
-	c.Assert(l.isReaderStale, check.IsFalse)
-	oriReader = l.r
-
-	for i := 0; i < 100; i++ {
-		row, err = l.GetRow(RowPtr{0, 0})
-		c.Assert(err, check.IsNil)
-		c.Assert(oriReader == l.r, check.IsTrue)
-		c.Assert(l.isReaderStale, check.IsFalse)
-	}
 }
 
 // Here we test situations where size of data is small, so no data is flushed to disk.