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executor: avoid concurrently update for SimpleLRUCache in ApplyCache (#50356) #50385

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8 changes: 7 additions & 1 deletion executor/apply_cache.go
Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,12 @@ func (c *applyCache) put(key applyCacheKey, val kvcache.Value) {
c.cache.Put(key, val)
}

func (c *applyCache) removeOldest() (kvcache.Key, kvcache.Value, bool) {
c.lock.Lock()
defer c.lock.Unlock()
return c.cache.RemoveOldest()
}

// Get gets a cache item according to cache key. It's thread-safe.
func (c *applyCache) Get(key applyCacheKey) (*chunk.List, error) {
value, hit := c.get(key)
Expand All @@ -83,7 +89,7 @@ func (c *applyCache) Set(key applyCacheKey, value *chunk.List) (bool, error) {
return false, nil
}
for mem+c.memTracker.BytesConsumed() > c.memCapacity {
evictedKey, evictedValue, evicted := c.cache.RemoveOldest()
evictedKey, evictedValue, evicted := c.removeOldest()
if !evicted {
return false, nil
}
Expand Down
59 changes: 59 additions & 0 deletions executor/apply_cache_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ package executor
import (
"strconv"
"strings"
"sync"
"testing"

"github.com/pingcap/tidb/parser/mysql"
Expand Down Expand Up @@ -77,3 +78,61 @@ func TestApplyCache(t *testing.T) {
require.NoError(t, err)
require.Nil(t, result)
}

func TestApplyCacheConcurrent(t *testing.T) {
ctx := mock.NewContext()
ctx.GetSessionVars().MemQuotaApplyCache = 100
applyCache, err := newApplyCache(ctx)
require.NoError(t, err)

fields := []*types.FieldType{types.NewFieldType(mysql.TypeLonglong)}
value := make([]*chunk.List, 2)
key := make([][]byte, 2)
for i := 0; i < 2; i++ {
value[i] = chunk.NewList(fields, 1, 1)
srcChunk := chunk.NewChunkWithCapacity(fields, 1)
srcChunk.AppendInt64(0, int64(i))
srcRow := srcChunk.GetRow(0)
value[i].AppendRow(srcRow)
key[i] = []byte(strings.Repeat(strconv.Itoa(i), 100))

// TODO: *chunk.List.GetMemTracker().BytesConsumed() is not accurate, fix it later.
require.Equal(t, int64(100), applyCacheKVMem(key[i], value[i]))
}

applyCache.Set(key[0], value[0])
var wg sync.WaitGroup
wg.Add(2)
var func1 = func() {
for i := 0; i < 100; i++ {
for {
result, err := applyCache.Get(key[0])
require.NoError(t, err)
if result != nil {
applyCache.Set(key[1], value[1])
break
}
}
}
wg.Done()
}
var func2 = func() {
for i := 0; i < 100; i++ {
for {
result, err := applyCache.Get(key[1])
require.NoError(t, err)
if result != nil {
applyCache.Set(key[0], value[0])
break
}
}
}
wg.Done()
}
go func1()
go func2()
wg.Wait()
result, err := applyCache.Get(key[0])
require.NoError(t, err)
require.NotNil(t, result)
}