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fix(vlog): upgrade discardStats to RWMutex and secure Iterate read path (#19431) #2309

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fix(vlog): upgrade discardStats to RWMutex and secure Iterate read path (#19431) #2309

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6 changes: 3 additions & 3 deletions discard.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ import (
// discardStats keeps track of the amount of data that could be discarded for
// a given logfile.
type discardStats struct {
sync.Mutex
sync.RWMutex

*z.MmapFile
opt Options
Expand Down Expand Up @@ -135,6 +135,8 @@ func (lf *discardStats) Update(fidu uint32, discard int64) int64 {
}

func (lf *discardStats) Iterate(f func(fid, stats uint64)) {
lf.RLock()
defer lf.RUnlock()
for slot := 0; slot < lf.nextEmptySlot; slot++ {
idx := 16 * slot
f(lf.get(idx), lf.get(idx+8))
Expand All @@ -143,8 +145,6 @@ func (lf *discardStats) Iterate(f func(fid, stats uint64)) {

// MaxDiscard returns the file id with maximum discard bytes.
func (lf *discardStats) MaxDiscard() (uint32, int64) {
lf.Lock()
defer lf.Unlock()

var maxFid, maxVal uint64
lf.Iterate(func(fid, val uint64) {
Expand Down
38 changes: 38 additions & 0 deletions discard_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ package badger

import (
"os"
"sync"
"testing"

"github.com/stretchr/testify/require"
Expand Down Expand Up @@ -64,3 +65,40 @@ func TestReloadDiscardStats(t *testing.T) {
require.Zero(t, ds2.Update(uint32(1), 0))
require.Equal(t, 1, int(ds2.Update(uint32(2), 0)))
}


func TestDiscardStats_ConcurrentRace(t *testing.T) {
dir, err := os.MkdirTemp("", "badger-test")
require.NoError(t, err)
defer removeDir(dir)

opt := DefaultOptions(dir)
db, err := Open(opt)
require.NoError(t, err)
defer db.Close()
ds := db.vlog.discardStats

var wg sync.WaitGroup
for i := 0; i < 20; i++ {
wg.Add(1)
go func(id uint32) {
defer wg.Done()
for j := 0; j < 100; j++ {
ds.Update(id, int64(j*10))
}
}(uint32(i))
}

for i := 0; i < 20; i++ {
wg.Add(1)
go func() {
defer wg.Done()
for j := 0; j < 100; j++ {
ds.Iterate(func(id, val uint64) {})
ds.MaxDiscard()
}
}()
}
wg.Wait()
}

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