From 727a9689382a059499c2da462e67f982dce672a7 Mon Sep 17 00:00:00 2001 From: Rishabh Mittal Date: Wed, 29 May 2024 14:18:42 -0700 Subject: [PATCH] infoschema: fix issue of information schema cache miss cause by schema version gap (#53445) (#53583) (#97) close pingcap/tidb#53428 Co-authored-by: Ti Chi Robot --- domain/domain.go | 2 + infoschema/cache.go | 66 +++++++++++++++++++- infoschema/cache_test.go | 126 +++++++++++++++++++++++++++++++++++++++ 3 files changed, 191 insertions(+), 3 deletions(-) diff --git a/domain/domain.go b/domain/domain.go index e9181ab260404..403a27fbc8cec 100644 --- a/domain/domain.go +++ b/domain/domain.go @@ -380,6 +380,8 @@ func (do *Domain) tryLoadSchemaDiffs(m *meta.Meta, usedVersion, newVersion int64 if diff == nil { // Empty diff means the txn of generating schema version is committed, but the txn of `runDDLJob` is not or fail. // It is safe to skip the empty diff because the infoschema is new enough and consistent. + logutil.BgLogger().Info("diff load InfoSchema get empty schema diff", zap.Int64("version", usedVersion)) + do.infoCache.InsertEmptySchemaVersion(usedVersion) continue } diffs = append(diffs, diff) diff --git a/infoschema/cache.go b/infoschema/cache.go index 1005ad4354424..beed6ae6e2965 100644 --- a/infoschema/cache.go +++ b/infoschema/cache.go @@ -40,6 +40,9 @@ type InfoCache struct { mu sync.RWMutex // cache is sorted by both SchemaVersion and timestamp in descending order, assume they have same order cache []schemaAndTimestamp + + // emptySchemaVersions stores schema version which has no schema_diff. + emptySchemaVersions map[int64]struct{} } type schemaAndTimestamp struct { @@ -50,7 +53,8 @@ type schemaAndTimestamp struct { // NewCache creates a new InfoCache. func NewCache(capacity int) *InfoCache { return &InfoCache{ - cache: make([]schemaAndTimestamp, 0, capacity), + cache: make([]schemaAndTimestamp, 0, capacity), + emptySchemaVersions: make(map[int64]struct{}), } } @@ -102,6 +106,11 @@ func (h *InfoCache) Len() int { return len(h.cache) } +// GetEmptySchemaVersions returns emptySchemaVersions, exports for testing. +func (h *InfoCache) GetEmptySchemaVersions() map[int64]struct{} { + return h.emptySchemaVersions +} + func (h *InfoCache) getSchemaByTimestampNoLock(ts uint64) (InfoSchema, bool) { logutil.BgLogger().Debug("SCHEMA CACHE get schema", zap.Uint64("timestamp", ts)) // search one by one instead of binary search, because the timestamp of a schema could be 0 @@ -110,14 +119,43 @@ func (h *InfoCache) getSchemaByTimestampNoLock(ts uint64) (InfoSchema, bool) { // thus it may have better performance than binary search for i, is := range h.cache { if is.timestamp == 0 || ts < uint64(is.timestamp) { + // is.timestamp == 0 means the schema ts is unknown, so we can't use it, then just skip it. + // ts < is.timestamp means the schema is newer than ts, so we can't use it too, just skip it to find the older one. continue } + // ts >= is.timestamp must be true after the above condition. if i == 0 { + // the first element is the latest schema, so we can return it directly. return is.infoschema, true } - if h.cache[i-1].infoschema.SchemaMetaVersion() == is.infoschema.SchemaMetaVersion()+1 && uint64(h.cache[i-1].timestamp) > ts { - return is.infoschema, true + + if uint64(h.cache[i-1].timestamp) > ts { + // The first condition is to make sure the cache[i-1].timestamp > ts >= cache[i].timestamp, then the current schema is suitable for ts. + lastVersion := h.cache[i-1].infoschema.SchemaMetaVersion() + currentVersion := is.infoschema.SchemaMetaVersion() + if lastVersion == currentVersion+1 { + // This condition is to make sure the schema version is continuous. If last(cache[i-1]) schema-version is 10, + // but current(cache[i]) schema-version is not 9, then current schema may not suitable for ts. + return is.infoschema, true + } + if lastVersion > currentVersion { + found := true + for ver := currentVersion + 1; ver < lastVersion; ver++ { + _, ok := h.emptySchemaVersions[ver] + if !ok { + found = false + break + } + } + if found { + // This condition is to make sure the schema version is continuous. If last(cache[i-1]) schema-version is 10, and + // current(cache[i]) schema-version is 8, then there is a gap exist, and if all the gap version can be found in cache.emptySchemaVersions + // which means those gap versions don't have schema info, then current schema is also suitable for ts. + return is.infoschema, true + } + } } + // current schema is not suitable for ts, then break the loop to avoid the unnecessary search. break } @@ -225,3 +263,25 @@ func (h *InfoCache) Insert(is InfoSchema, schemaTS uint64) bool { return true } + +// InsertEmptySchemaVersion inserts empty schema version into a map. If exceeded the cache capacity, remove the oldest version. +func (h *InfoCache) InsertEmptySchemaVersion(version int64) { + h.mu.Lock() + defer h.mu.Unlock() + + h.emptySchemaVersions[version] = struct{}{} + if len(h.emptySchemaVersions) > cap(h.cache) { + // remove oldest version. + versions := make([]int64, 0, len(h.emptySchemaVersions)) + for ver := range h.emptySchemaVersions { + versions = append(versions, ver) + } + sort.Slice(versions, func(i, j int) bool { return versions[i] < versions[j] }) + for _, ver := range versions { + delete(h.emptySchemaVersions, ver) + if len(h.emptySchemaVersions) <= cap(h.cache) { + break + } + } + } +} diff --git a/infoschema/cache_test.go b/infoschema/cache_test.go index b3957a9660b29..45d9382e7c8de 100644 --- a/infoschema/cache_test.go +++ b/infoschema/cache_test.go @@ -292,3 +292,129 @@ func TestCacheWithSchemaTsZero(t *testing.T) { checkFn(85, 100, true) require.Equal(t, 16, ic.Size()) } + +func TestCacheWithSchemaTsZero(t *testing.T) { + ic := infoschema.NewCache(16) + require.NotNil(t, ic) + + for i := 1; i <= 8; i++ { + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, int64(i)), uint64(i)) + } + + checkFn := func(start, end int64, exist bool) { + require.True(t, start <= end) + latestSchemaVersion := ic.GetLatest().SchemaMetaVersion() + for ts := start; ts <= end; ts++ { + is := ic.GetBySnapshotTS(uint64(ts)) + if exist { + require.NotNil(t, is, fmt.Sprintf("ts %d", ts)) + if ts > latestSchemaVersion { + require.Equal(t, latestSchemaVersion, is.SchemaMetaVersion(), fmt.Sprintf("ts %d", ts)) + } else { + require.Equal(t, ts, is.SchemaMetaVersion(), fmt.Sprintf("ts %d", ts)) + } + } else { + require.Nil(t, is, fmt.Sprintf("ts %d", ts)) + } + } + } + checkFn(1, 8, true) + checkFn(8, 10, true) + + // mock for meet error There is no Write MVCC info for the schema version + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, 9), 0) + checkFn(1, 7, true) + checkFn(8, 9, false) + checkFn(9, 10, false) + + for i := 10; i <= 16; i++ { + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, int64(i)), uint64(i)) + checkFn(1, 7, true) + checkFn(8, 9, false) + checkFn(10, 16, true) + } + require.Equal(t, 16, ic.Size()) + + // refill the cache + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, 9), 9) + checkFn(1, 16, true) + require.Equal(t, 16, ic.Size()) + + // Test more than capacity + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, 17), 17) + checkFn(1, 1, false) + checkFn(2, 17, true) + checkFn(2, 20, true) + require.Equal(t, 16, ic.Size()) + + // Test for there is a hole in the middle. + ic = infoschema.NewCache(16) + + // mock for restart with full load the latest version schema. + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, 100), 100) + checkFn(1, 99, false) + checkFn(100, 100, true) + + for i := 1; i <= 16; i++ { + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, int64(i)), uint64(i)) + } + checkFn(1, 1, false) + checkFn(2, 15, true) + checkFn(16, 16, false) + checkFn(100, 100, true) + require.Equal(t, 16, ic.Size()) + + for i := 85; i < 100; i++ { + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, int64(i)), uint64(i)) + } + checkFn(1, 84, false) + checkFn(85, 100, true) + require.Equal(t, 16, ic.Size()) + + // Test cache with schema version hole, which is cause by schema version doesn't has related schema-diff. + ic = infoschema.NewCache(16) + require.NotNil(t, ic) + for i := 1; i <= 8; i++ { + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, int64(i)), uint64(i)) + } + checkFn(1, 10, true) + // mock for schema version hole, schema-version 9 is missing. + ic.Insert(infoschema.MockInfoSchemaWithSchemaVer(nil, 10), 10) + checkFn(1, 7, true) + // without empty schema version map, get snapshot by ts 8, 9 will both failed. + checkFn(8, 9, false) + checkFn(10, 10, true) + // add empty schema version 9. + ic.InsertEmptySchemaVersion(9) + // after set empty schema version, get snapshot by ts 8, 9 will both success. + checkFn(1, 8, true) + checkFn(10, 10, true) + is := ic.GetBySnapshotTS(uint64(9)) + require.NotNil(t, is) + // since schema version 9 is empty, so get by ts 9 will get schema which version is 8. + require.Equal(t, int64(8), is.SchemaMetaVersion()) +} + +func TestCacheEmptySchemaVersion(t *testing.T) { + ic := infoschema.NewCache(16) + require.NotNil(t, ic) + require.Equal(t, 0, len(ic.GetEmptySchemaVersions())) + for i := 0; i < 16; i++ { + ic.InsertEmptySchemaVersion(int64(i)) + } + emptyVersions := ic.GetEmptySchemaVersions() + require.Equal(t, 16, len(emptyVersions)) + for i := 0; i < 16; i++ { + _, ok := emptyVersions[int64(i)] + require.True(t, ok) + } + for i := 16; i < 20; i++ { + ic.InsertEmptySchemaVersion(int64(i)) + } + emptyVersions = ic.GetEmptySchemaVersions() + require.Equal(t, 16, len(emptyVersions)) + for i := 4; i < 20; i++ { + _, ok := emptyVersions[int64(i)] + require.True(t, ok) + } +}