*: make changes to tidb_schema_cache_size effective immediately (#54279)

ref pingcap/tidb#50959

pkg/domain/domain_sysvars.go

@@ -40,6 +40,8 @@ func (do *Domain) initDomainSysVars() {
 	setGlobalResourceControlFunc := do.setGlobalResourceControl
 	variable.SetGlobalResourceControl.Store(&setGlobalResourceControlFunc)
 	variable.SetLowResolutionTSOUpdateInterval = do.setLowResolutionTSOUpdateInterval
+
+	variable.ChangeSchemaCacheSize = do.changeSchemaCacheSize
 }
 
 // setStatsCacheCapacity sets statsCache cap
@@ -115,3 +117,9 @@ func (do *Domain) setExternalTimestamp(ctx context.Context, ts uint64) error {
 func (do *Domain) getExternalTimestamp(ctx context.Context) (uint64, error) {
 	return do.store.GetOracle().GetExternalTimestamp(ctx)
 }
+
+func (do *Domain) changeSchemaCacheSize(size uint64) {
+	if size > 0 {
+		do.infoCache.Data.SetCacheCapacity(size)
+	}
+}

pkg/infoschema/infoschema_v2.go

@@ -197,6 +197,11 @@ func (isd *Data) CacheCapacity() uint64 {
 	return isd.tableCache.Capacity()
 }
 
+// SetCacheCapacity sets the cache capacity size in bytes.
+func (isd *Data) SetCacheCapacity(capacity uint64) {
+	isd.tableCache.SetCapacityAndWaitEvict(capacity)
+}
+
 func (isd *Data) add(item tableItem, tbl table.Table) {
 	isd.byID.Set(item)
 	isd.byName.Set(item)

pkg/infoschema/sieve.go

@@ -103,6 +103,21 @@ func (s *Sieve[K, V]) SetCapacity(capacity uint64) {
 	s.hook.onUpdateLimit(capacity)
 }
 
+func (s *Sieve[K, V]) SetCapacityAndWaitEvict(capacity uint64) {
+	s.SetCapacity(capacity)
+	for {
+		s.mu.Lock()
+		if s.size <= s.capacity {
+			s.mu.Unlock()
+			break
+		}
+		for i := 0; s.size > s.capacity && i < 10; i++ {
+			s.evict()
+		}
+		s.mu.Unlock()
+	}
+}
+
 func (s *Sieve[K, V]) Capacity() uint64 {
 	s.mu.Lock()
 	defer s.mu.Unlock()

pkg/sessionctx/variable/sysvar.go

@@ -3154,6 +3154,9 @@ var defaultSysVars = []*SysVar{
 			if err != nil {
 				return err
 			}
+			if SchemaCacheSize.Load() != bt && ChangeSchemaCacheSize != nil {
+				ChangeSchemaCacheSize(bt)
+			}
 			SchemaCacheSize.Store(bt)
 			SchemaCacheSizeOriginText.Store(str)
 			return nil

pkg/sessionctx/variable/tidb_vars.go

@@ -1647,6 +1647,8 @@ var (
 	ValidateCloudStorageURI func(ctx context.Context, uri string) error
 	// SetLowResolutionTSOUpdateInterval is the func registered by domain to set slow resolution tso update interval.
 	SetLowResolutionTSOUpdateInterval func(interval time.Duration) error = nil
+	// ChangeSchemaCacheSize is called when tidb_schema_cache_size is changed.
+	ChangeSchemaCacheSize func(size uint64)
 )
 
 // Hooks functions for Cluster Resource Control.