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planner: update the underlying binding cache structure (pingcap#58481)
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qw4990 authored Dec 24, 2024
1 parent b079b5f commit a21c95b
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Showing 14 changed files with 162 additions and 201 deletions.
4 changes: 1 addition & 3 deletions pkg/bindinfo/BUILD.bazel
Original file line number Diff line number Diff line change
Expand Up @@ -32,12 +32,10 @@ go_library(
"//pkg/util/hack",
"//pkg/util/hint",
"//pkg/util/intest",
"//pkg/util/kvcache",
"//pkg/util/mathutil",
"//pkg/util/memory",
"//pkg/util/parser",
"//pkg/util/sqlexec",
"//pkg/util/stringutil",
"@com_github_dgraph_io_ristretto//:ristretto",
"@com_github_pingcap_errors//:errors",
"@com_github_pingcap_failpoint//:failpoint",
"@com_github_pkg_errors//:errors",
Expand Down
199 changes: 59 additions & 140 deletions pkg/bindinfo/binding_cache.go
Original file line number Diff line number Diff line change
Expand Up @@ -20,18 +20,15 @@ import (
"sync/atomic"
"time"

"github.com/dgraph-io/ristretto"
"github.com/pingcap/tidb/pkg/bindinfo/internal/logutil"
"github.com/pingcap/tidb/pkg/bindinfo/norm"
"github.com/pingcap/tidb/pkg/metrics"
"github.com/pingcap/tidb/pkg/parser"
"github.com/pingcap/tidb/pkg/parser/ast"
"github.com/pingcap/tidb/pkg/sessionctx"
"github.com/pingcap/tidb/pkg/sessionctx/variable"
"github.com/pingcap/tidb/pkg/util/hack"
"github.com/pingcap/tidb/pkg/util/intest"
"github.com/pingcap/tidb/pkg/util/kvcache"
"github.com/pingcap/tidb/pkg/util/mathutil"
"github.com/pingcap/tidb/pkg/util/memory"
"github.com/pingcap/tidb/pkg/util/stringutil"
"go.uber.org/zap"
)
Expand Down Expand Up @@ -59,14 +56,14 @@ type digestBiMap interface {
// Del deletes the pair of noDBDigest and sqlDigest.
Del(sqlDigest string)

// All returns all the sqlDigests.
All() (sqlDigests []string)

// NoDBDigest2SQLDigest converts noDBDigest to sqlDigest.
NoDBDigest2SQLDigest(noDBDigest string) []string

// SQLDigest2NoDBDigest converts sqlDigest to noDBDigest.
SQLDigest2NoDBDigest(sqlDigest string) string

// Copy copies this digestBiMap.
Copy() digestBiMap
}

type digestBiMapImpl struct {
Expand Down Expand Up @@ -116,6 +113,17 @@ func (b *digestBiMapImpl) Del(sqlDigest string) {
delete(b.sqlDigest2noDBDigest, sqlDigest)
}

// All returns all the sqlDigests.
func (b *digestBiMapImpl) All() []string {
b.mu.RLock()
defer b.mu.RUnlock()
sqlDigests := make([]string, 0, len(b.sqlDigest2noDBDigest))
for sqlDigest := range b.sqlDigest2noDBDigest {
sqlDigests = append(sqlDigests, sqlDigest)
}
return sqlDigests
}

// NoDBDigest2SQLDigest converts noDBDigest to sqlDigest.
func (b *digestBiMapImpl) NoDBDigest2SQLDigest(noDBDigest string) []string {
b.mu.RLock()
Expand All @@ -130,26 +138,6 @@ func (b *digestBiMapImpl) SQLDigest2NoDBDigest(sqlDigest string) string {
return b.sqlDigest2noDBDigest[sqlDigest]
}

// Copy copies this digestBiMap.
func (b *digestBiMapImpl) Copy() digestBiMap {
b.mu.RLock()
defer b.mu.RUnlock()
noDBDigest2SQLDigest := make(map[string][]string, len(b.noDBDigest2SQLDigest))
for k, list := range b.noDBDigest2SQLDigest {
newList := make([]string, len(list))
copy(newList, list)
noDBDigest2SQLDigest[k] = newList
}
sqlDigest2noDBDigest := make(map[string]string, len(b.sqlDigest2noDBDigest))
for k, v := range b.sqlDigest2noDBDigest {
sqlDigest2noDBDigest[k] = v
}
return &digestBiMapImpl{
noDBDigest2SQLDigest: noDBDigest2SQLDigest,
sqlDigest2noDBDigest: sqlDigest2noDBDigest,
}
}

// BindingCache is the interface for the cache of the SQL plan bindings.
type BindingCache interface {
// MatchingBinding supports cross-db matching on bindings.
Expand All @@ -170,104 +158,40 @@ type BindingCache interface {
GetMemCapacity() int64
// Size returns the number of items in the cache.
Size() int
// Close closes the cache.
Close()
}

// bindingCache uses the LRU cache to store the bindings.
// The key of the LRU cache is original sql, the value is a slice of Bindings.
// Note: The bindingCache should be accessed with lock.
type bindingCache struct {
lock sync.RWMutex
digestBiMap digestBiMap // mapping between noDBDigest and sqlDigest, used to support cross-db binding.
cache *kvcache.SimpleLRUCache // the underlying cache to store the bindings.
memCapacity int64
memTracker *memory.Tracker // track memory usage.
// TODO: use the underlying cache structure to track and control the memory usage, and remove
// memCapacity and memTracker to simplify the code.
digestBiMap digestBiMap // mapping between noDBDigest and sqlDigest, used to support cross-db binding.
cache *ristretto.Cache // the underlying cache to store the bindings.

// loadBindingFromStorageFunc is used to load binding from storage if cache miss.
loadBindingFromStorageFunc func(sctx sessionctx.Context, sqlDigest string) (Bindings, error)
}

type bindingCacheKey string

func (key bindingCacheKey) Hash() []byte {
return hack.Slice(string(key))
}

func calcBindCacheKVMem(key bindingCacheKey, value Bindings) int64 {
var valMem int64
valMem += int64(value.size())
return int64(len(key.Hash())) + valMem
}

func newBindCache(bindingLoad func(sctx sessionctx.Context, sqlDigest string) (Bindings, error)) BindingCache {
// since bindingCache controls the memory usage by itself, set the capacity of
// the underlying LRUCache to max to close its memory control
cache := kvcache.NewSimpleLRUCache(mathutil.MaxUint, 0, 0)
cache, _ := ristretto.NewCache(&ristretto.Config{
NumCounters: 1e6,
MaxCost: variable.MemQuotaBindingCache.Load(),
BufferItems: 64,
Cost: func(value any) int64 {
return int64(value.(Bindings).size())
},
Metrics: true,
IgnoreInternalCost: true,
})
c := bindingCache{
cache: cache,
digestBiMap: newDigestBiMap(),
memCapacity: variable.MemQuotaBindingCache.Load(),
memTracker: memory.NewTracker(memory.LabelForBindCache, -1),
loadBindingFromStorageFunc: bindingLoad,
}
return &c
}

// get gets a cache item according to cache key. It's not thread-safe.
// Note: Only other functions of the bindingCache file can use this function.
// Don't use this function directly in other files in bindinfo package.
// The return value is not read-only, but it is only can be used in other functions which are also in the bind_cache.go.
func (c *bindingCache) get(key bindingCacheKey) Bindings {
value, hit := c.cache.Get(key)
if !hit {
return nil
}
typedValue := value.(Bindings)
return typedValue
}

// set inserts an item to the cache. It's not thread-safe.
// Only other functions of the bindingCache can use this function.
// The set operation will return error message when the memory usage of binding_cache exceeds its capacity.
func (c *bindingCache) set(key bindingCacheKey, value Bindings) (ok bool, err error) {
mem := calcBindCacheKVMem(key, value)
if mem > c.memCapacity { // ignore this kv pair if its size is too large
err = errors.New("The memory usage of all available bindings exceeds the cache's mem quota. As a result, all available bindings cannot be held on the cache. Please increase the value of the system variable 'tidb_mem_quota_binding_cache' and execute 'admin reload bindings' to ensure that all bindings exist in the cache and can be used normally")
return
}
bindings := c.get(key)
if bindings != nil {
// Remove the origin key-value pair.
mem -= calcBindCacheKVMem(key, bindings)
}
for mem+c.memTracker.BytesConsumed() > c.memCapacity {
err = errors.New("The memory usage of all available bindings exceeds the cache's mem quota. As a result, all available bindings cannot be held on the cache. Please increase the value of the system variable 'tidb_mem_quota_binding_cache' and execute 'admin reload bindings' to ensure that all bindings exist in the cache and can be used normally")
evictedKey, evictedValue, evicted := c.cache.RemoveOldest()
if !evicted {
return
}
c.memTracker.Consume(-calcBindCacheKVMem(evictedKey.(bindingCacheKey), evictedValue.(Bindings)))
}
c.memTracker.Consume(mem)
c.cache.Put(key, value)
ok = true
return
}

// delete remove an item from the cache. It's not thread-safe.
// Only other functions of the bindingCache can use this function.
func (c *bindingCache) delete(key bindingCacheKey) bool {
bindings := c.get(key)
if bindings != nil {
mem := calcBindCacheKVMem(key, bindings)
c.cache.Delete(key)
c.memTracker.Consume(-mem)
return true
}
return false
}

func (c *bindingCache) shouldMetric() bool {
return c.loadBindingFromStorageFunc != nil // only metric for GlobalBindingCache, whose loadBindingFromStorageFunc is not nil.
}
Expand Down Expand Up @@ -367,31 +291,28 @@ func (c *bindingCache) loadFromStore(sctx sessionctx.Context, missingSQLDigest [
// The return value is not read-only, but it shouldn't be changed in the caller functions.
// The function is thread-safe.
func (c *bindingCache) GetBinding(sqlDigest string) Bindings {
c.lock.RLock()
defer c.lock.RUnlock()
return c.get(bindingCacheKey(sqlDigest))
v, ok := c.cache.Get(sqlDigest)
if !ok {
return nil
}
return v.(Bindings)
}

// GetAllBindings return all the bindings from the bindingCache.
// The return value is not read-only, but it shouldn't be changed in the caller functions.
// The function is thread-safe.
func (c *bindingCache) GetAllBindings() Bindings {
c.lock.RLock()
defer c.lock.RUnlock()
values := c.cache.Values()
bindings := make(Bindings, 0, len(values))
for _, vals := range values {
bindings = append(bindings, vals.(Bindings)...)
sqlDigests := c.digestBiMap.All()
bindings := make(Bindings, 0, len(sqlDigests))
for _, sqlDigest := range sqlDigests {
bindings = append(bindings, c.GetBinding(sqlDigest)...)
}
return bindings
}

// SetBinding sets the Bindings to the cache.
// The function is thread-safe.
func (c *bindingCache) SetBinding(sqlDigest string, bindings Bindings) (err error) {
c.lock.Lock()
defer c.lock.Unlock()

// prepare noDBDigests for all bindings
noDBDigests := make([]string, 0, len(bindings))
p := parser.New()
Expand All @@ -404,53 +325,51 @@ func (c *bindingCache) SetBinding(sqlDigest string, bindings Bindings) (err erro
noDBDigests = append(noDBDigests, noDBDigest)
}

for i, binding := range bindings {
c.digestBiMap.Add(noDBDigests[i], binding.SQLDigest)
for i := range bindings {
c.digestBiMap.Add(noDBDigests[i], sqlDigest)
}

// NOTE: due to LRU eviction, the underlying BindingCache state might be inconsistent with noDBDigest2SQLDigest and
// sqlDigest2noDBDigest, but it's acceptable, just return cache-miss in that case.
cacheKey := bindingCacheKey(sqlDigest)
_, err = c.set(cacheKey, bindings)
// NOTE: due to LRU eviction, the underlying BindingCache state might be inconsistent with digestBiMap,
// but it's acceptable, the optimizer will load the binding when cache-miss.
// NOTE: the Set might fail if the operation is too frequent, but binding update is a low-frequently operation, so
// this risk seems acceptable.
// TODO: handle the Set failure more gracefully.
c.cache.Set(sqlDigest, bindings, 0)
c.cache.Wait()
return
}

// RemoveBinding removes the Bindings which has same originSQL with specified Bindings.
// The function is thread-safe.
func (c *bindingCache) RemoveBinding(sqlDigest string) {
c.lock.Lock()
defer c.lock.Unlock()
c.digestBiMap.Del(sqlDigest)
c.delete(bindingCacheKey(sqlDigest))
c.cache.Del(sqlDigest)
}

// SetMemCapacity sets the memory capacity for the cache.
// The function is thread-safe.
func (c *bindingCache) SetMemCapacity(capacity int64) {
c.lock.Lock()
defer c.lock.Unlock()
// Only change the capacity size without affecting the cached bindings
c.memCapacity = capacity
c.cache.UpdateMaxCost(capacity)
}

// GetMemUsage get the memory Usage for the cache.
// The function is thread-safe.
func (c *bindingCache) GetMemUsage() int64 {
c.lock.Lock()
defer c.lock.Unlock()
return c.memTracker.BytesConsumed()
return int64(c.cache.Metrics.CostAdded() - c.cache.Metrics.CostEvicted())
}

// GetMemCapacity get the memory capacity for the cache.
// The function is thread-safe.
func (c *bindingCache) GetMemCapacity() int64 {
c.lock.Lock()
defer c.lock.Unlock()
return c.memCapacity
return c.cache.MaxCost()
}

func (c *bindingCache) Size() int {
c.lock.Lock()
defer c.lock.Unlock()
return c.cache.Size()
return int(c.cache.Metrics.KeysAdded() - c.cache.Metrics.KeysEvicted())
}

// Close closes the cache.
func (c *bindingCache) Close() {
c.cache.Clear()
c.cache.Close()
c.cache.Wait()
}
22 changes: 17 additions & 5 deletions pkg/bindinfo/binding_cache_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ package bindinfo

import (
"testing"
"time"

"github.com/pingcap/tidb/pkg/bindinfo/norm"
"github.com/pingcap/tidb/pkg/parser"
Expand Down Expand Up @@ -70,9 +71,13 @@ func TestCrossDBBindingCache(t *testing.T) {

func TestBindCache(t *testing.T) {
bindings := Bindings{{BindSQL: "SELECT * FROM t1"}}
kvSize := len("digest1") + int(bindings.size())
kvSize := int(bindings.size())
defer func(v int64) {
variable.MemQuotaBindingCache.Store(v)
}(variable.MemQuotaBindingCache.Load())
variable.MemQuotaBindingCache.Store(int64(kvSize*3) - 1)
bindCache := newBindCache(nil)
defer bindCache.Close()

err := bindCache.SetBinding("digest1", bindings)
require.Nil(t, err)
Expand All @@ -83,9 +88,16 @@ func TestBindCache(t *testing.T) {
require.NotNil(t, bindCache.GetBinding("digest2"))

err = bindCache.SetBinding("digest3", bindings)
require.NotNil(t, err) // exceed the memory limit
require.NotNil(t, bindCache.GetBinding("digest2"))
require.Nil(t, err)
require.NotNil(t, bindCache.GetBinding("digest3"))

require.Nil(t, bindCache.GetBinding("digest1")) // digest1 is evicted
require.NotNil(t, bindCache.GetBinding("digest2")) // digest2 is still in the cache
require.Eventually(t, func() bool {
hit := 0
for _, digest := range []string{"digest1", "digest2", "digest3"} {
if bindCache.GetBinding(digest) != nil {
hit++
}
}
return hit == 2
}, time.Second*5, time.Millisecond*100)
}
8 changes: 8 additions & 0 deletions pkg/bindinfo/global_handle.go
Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,9 @@ type GlobalBindingHandle interface {
// GetMemCapacity returns the memory capacity for the bind cache.
GetMemCapacity() (memCapacity int64)

// Close closes the binding cache.
CloseCache()

variable.Statistics
}

Expand Down Expand Up @@ -606,6 +609,11 @@ func (h *globalBindingHandle) Stats(_ *variable.SessionVars) (map[string]any, er
return m, nil
}

// Close closes the binding cache.
func (h *globalBindingHandle) CloseCache() {
h.bindingCache.Close()
}

// LoadBindingsFromStorageToCache loads global bindings from storage to the memory cache.
func (h *globalBindingHandle) LoadBindingsFromStorage(sctx sessionctx.Context, sqlDigest string) (Bindings, error) {
if sqlDigest == "" {
Expand Down
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