sql: move histogram decoding into the stats cache

Currently the stats cache exposes the encoded histogram data, and the
opt catalog decodes it. The problem is that opt catalog objects are
not shared across connections so this is inefficient (especially in
memory usage).

This change moves the decoding into the stats cache. The opt catalog
objects now simply point to the data computed by the cache.

There are still inefficiencies to improve on in the future: the opt
catalog can hold on to multiple versions of tables, so we will keep
many versions of histograms "alive".

Informs cockroachdb#41206.
Informs cockroachdb#40922.

Release justification: fix for new functionality.

Release note: None

pkg/ccl/backupccl/backup.go

@@ -1045,7 +1045,7 @@ func backupPlanHook(
 		}
 
 		statsCache := p.ExecCfg().TableStatsCache
-		tableStatistics := make([]*stats.TableStatistic, 0)
+		tableStatistics := make([]*stats.TableStatisticProto, 0)
 		var tables []*sqlbase.TableDescriptor
 		for _, desc := range targetDescs {
 			if dbDesc := desc.GetDatabase(); dbDesc != nil {
@@ -1064,7 +1064,9 @@ func backupPlanHook(
 				if err != nil {
 					return err
 				}
-				tableStatistics = append(tableStatistics, tableStatisticsAcc...)
+				for i := range tableStatisticsAcc {
+					tableStatistics = append(tableStatistics, &tableStatisticsAcc[i].TableStatisticProto)
+				}
 			}
 		}
 

pkg/ccl/backupccl/backup.proto

@@ -101,7 +101,7 @@ message BackupDescriptor {
                 (gogoproto.customtype) = "github.com/cockroachdb/cockroach/pkg/util/uuid.UUID"];
   repeated string partition_descriptor_filenames = 19;
   repeated string locality_kvs = 20 [(gogoproto.customname) = "LocalityKVs"];
-  repeated sql.stats.TableStatistic statistics = 21;
+  repeated sql.stats.TableStatisticProto statistics = 21;
 }
 
 message BackupPartitionDescriptor{

pkg/ccl/backupccl/restore.go

@@ -1644,7 +1644,7 @@ type restoreResumer struct {
 	databases      []*sqlbase.DatabaseDescriptor
 	tables         []*sqlbase.TableDescriptor
 	exec           sqlutil.InternalExecutor
-	latestStats    []*stats.TableStatistic
+	latestStats    []*stats.TableStatisticProto
 	statsRefresher *stats.Refresher
 }
 
@@ -1656,8 +1656,8 @@ type restoreResumer struct {
 // table is being restored.
 func remapRelevantStatistics(
 	backup BackupDescriptor, tableRewrites TableRewriteMap,
-) []*stats.TableStatistic {
-	relevantTableStatistics := make([]*stats.TableStatistic, 0, len(backup.Statistics))
+) []*stats.TableStatisticProto {
+	relevantTableStatistics := make([]*stats.TableStatisticProto, 0, len(backup.Statistics))
 
 	for i := range backup.Statistics {
 		stat := backup.Statistics[i]

pkg/sql/opt_catalog.go

@@ -26,7 +26,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
 	"github.com/cockroachdb/cockroach/pkg/sql/stats"
 	"github.com/cockroachdb/cockroach/pkg/util"
-	"github.com/cockroachdb/cockroach/pkg/util/encoding"
 	"github.com/cockroachdb/errors"
 )
 
@@ -1001,22 +1000,14 @@ func (oi *optIndex) PartitionByListPrefixes() []tree.Datums {
 }
 
 type optTableStat struct {
-	createdAt      time.Time
+	stat           *stats.TableStatistic
 	columnOrdinals []int
-	rowCount       uint64
-	distinctCount  uint64
-	nullCount      uint64
-	histogram      []cat.HistogramBucket
 }
 
 var _ cat.TableStatistic = &optTableStat{}
 
 func (os *optTableStat) init(tab *optTable, stat *stats.TableStatistic) (ok bool, _ error) {
-	os.createdAt = stat.CreatedAt
-	os.rowCount = stat.RowCount
-	os.distinctCount = stat.DistinctCount
-	os.nullCount = stat.NullCount
-
+	os.stat = stat
 	os.columnOrdinals = make([]int, len(stat.ColumnIDs))
 	for i, c := range stat.ColumnIDs {
 		var ok bool
@@ -1028,31 +1019,13 @@ func (os *optTableStat) init(tab *optTable, stat *stats.TableStatistic) (ok bool
 		}
 	}
 
-	if stat.Histogram != nil {
-		os.histogram = make([]cat.HistogramBucket, len(stat.Histogram.Buckets))
-		typ := &stat.Histogram.ColumnType
-		var a sqlbase.DatumAlloc
-		for i := range os.histogram {
-			bucket := &stat.Histogram.Buckets[i]
-			datum, _, err := sqlbase.DecodeTableKey(&a, typ, bucket.UpperBound, encoding.Ascending)
-			if err != nil {
-				return false, err
-			}
-			os.histogram[i] = cat.HistogramBucket{
-				NumEq:         float64(bucket.NumEq),
-				NumRange:      float64(bucket.NumRange),
-				DistinctRange: bucket.DistinctRange,
-				UpperBound:    datum,
-			}
-		}
-	}
 	return true, nil
 }
 
 func (os *optTableStat) equals(other *optTableStat) bool {
 	// Two table statistics are considered equal if they have been created at the
 	// same time, on the same set of columns.
-	if os.createdAt != other.createdAt || len(os.columnOrdinals) != len(other.columnOrdinals) {
+	if os.CreatedAt() != other.CreatedAt() || len(os.columnOrdinals) != len(other.columnOrdinals) {
 		return false
 	}
 	for i, c := range os.columnOrdinals {
@@ -1065,7 +1038,7 @@ func (os *optTableStat) equals(other *optTableStat) bool {
 
 // CreatedAt is part of the cat.TableStatistic interface.
 func (os *optTableStat) CreatedAt() time.Time {
-	return os.createdAt
+	return os.stat.CreatedAt
 }
 
 // ColumnCount is part of the cat.TableStatistic interface.
@@ -1080,22 +1053,22 @@ func (os *optTableStat) ColumnOrdinal(i int) int {
 
 // RowCount is part of the cat.TableStatistic interface.
 func (os *optTableStat) RowCount() uint64 {
-	return os.rowCount
+	return os.stat.RowCount
 }
 
 // DistinctCount is part of the cat.TableStatistic interface.
 func (os *optTableStat) DistinctCount() uint64 {
-	return os.distinctCount
+	return os.stat.DistinctCount
 }
 
 // NullCount is part of the cat.TableStatistic interface.
 func (os *optTableStat) NullCount() uint64 {
-	return os.nullCount
+	return os.stat.NullCount
 }
 
 // Histogram is part of the cat.TableStatistic interface.
 func (os *optTableStat) Histogram() []cat.HistogramBucket {
-	return os.histogram
+	return os.stat.Histogram
 }
 
 // optFamily is a wrapper around sqlbase.ColumnFamilyDescriptor that keeps a

pkg/sql/stats/delete_stats_test.go

@@ -38,7 +38,7 @@ func TestDeleteOldStatsForColumns(t *testing.T) {
 
 	// The test data must be ordered by CreatedAt DESC so the calculated set of
 	// expected deleted stats is correct.
-	testData := []TableStatistic{
+	testData := []TableStatisticProto{
 		{
 			TableID:       sqlbase.ID(100),
 			StatisticID:   1,

pkg/sql/stats/new_stat.go

@@ -28,7 +28,7 @@ func InsertNewStats(
 	ctx context.Context,
 	executor sqlutil.InternalExecutor,
 	txn *client.Txn,
-	tableStats []*TableStatistic,
+	tableStats []*TableStatisticProto,
 ) error {
 	var err error
 	for _, statistic := range tableStats {
@@ -42,7 +42,7 @@ func InsertNewStats(
 			int64(statistic.RowCount),
 			int64(statistic.DistinctCount),
 			int64(statistic.NullCount),
-			statistic.Histogram,
+			statistic.HistogramData,
 		)
 		if err != nil {
 			return err

pkg/sql/stats/stats_cache.go

@@ -17,17 +17,28 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/gossip"
 	"github.com/cockroachdb/cockroach/pkg/internal/client"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
+	"github.com/cockroachdb/cockroach/pkg/sql/opt/cat"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
 	"github.com/cockroachdb/cockroach/pkg/sql/sqlutil"
 	"github.com/cockroachdb/cockroach/pkg/sql/types"
 	"github.com/cockroachdb/cockroach/pkg/util/cache"
+	"github.com/cockroachdb/cockroach/pkg/util/encoding"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/protoutil"
 	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
 	"github.com/pkg/errors"
 )
 
+// A TableStatistic object holds a statistic for a particular column or group
+// of columns.
+type TableStatistic struct {
+	TableStatisticProto
+
+	// Histogram is the decoded histogram data.
+	Histogram []cat.HistogramBucket
+}
+
 // A TableStatisticsCache contains two underlying LRU caches:
 // (1) A cache of []*TableStatistic objects, keyed by table ID.
 //     Each entry consists of all the statistics for different columns and
@@ -262,33 +273,53 @@ func parseStats(datums tree.Datums) (*TableStatistic, error) {
 	}
 
 	// Extract datum values.
-	tableStatistic := &TableStatistic{
-		TableID:       sqlbase.ID((int32)(*datums[tableIDIndex].(*tree.DInt))),
-		StatisticID:   (uint64)(*datums[statisticsIDIndex].(*tree.DInt)),
-		CreatedAt:     datums[createdAtIndex].(*tree.DTimestamp).Time,
-		RowCount:      (uint64)(*datums[rowCountIndex].(*tree.DInt)),
-		DistinctCount: (uint64)(*datums[distinctCountIndex].(*tree.DInt)),
-		NullCount:     (uint64)(*datums[nullCountIndex].(*tree.DInt)),
+	res := &TableStatistic{
+		TableStatisticProto: TableStatisticProto{
+			TableID:       sqlbase.ID((int32)(*datums[tableIDIndex].(*tree.DInt))),
+			StatisticID:   (uint64)(*datums[statisticsIDIndex].(*tree.DInt)),
+			CreatedAt:     datums[createdAtIndex].(*tree.DTimestamp).Time,
+			RowCount:      (uint64)(*datums[rowCountIndex].(*tree.DInt)),
+			DistinctCount: (uint64)(*datums[distinctCountIndex].(*tree.DInt)),
+			NullCount:     (uint64)(*datums[nullCountIndex].(*tree.DInt)),
+		},
 	}
 	columnIDs := datums[columnIDsIndex].(*tree.DArray)
-	tableStatistic.ColumnIDs = make([]sqlbase.ColumnID, len(columnIDs.Array))
+	res.ColumnIDs = make([]sqlbase.ColumnID, len(columnIDs.Array))
 	for i, d := range columnIDs.Array {
-		tableStatistic.ColumnIDs[i] = sqlbase.ColumnID((int32)(*d.(*tree.DInt)))
+		res.ColumnIDs[i] = sqlbase.ColumnID((int32)(*d.(*tree.DInt)))
 	}
 	if datums[nameIndex] != tree.DNull {
-		tableStatistic.Name = string(*datums[nameIndex].(*tree.DString))
+		res.Name = string(*datums[nameIndex].(*tree.DString))
 	}
 	if datums[histogramIndex] != tree.DNull {
-		tableStatistic.Histogram = &HistogramData{}
+		res.HistogramData = &HistogramData{}
 		if err := protoutil.Unmarshal(
 			[]byte(*datums[histogramIndex].(*tree.DBytes)),
-			tableStatistic.Histogram,
+			res.HistogramData,
 		); err != nil {
 			return nil, err
 		}
+
+		// Decode the histogram data so that it's usable by the opt catalog.
+		res.Histogram = make([]cat.HistogramBucket, len(res.HistogramData.Buckets))
+		typ := &res.HistogramData.ColumnType
+		var a sqlbase.DatumAlloc
+		for i := range res.Histogram {
+			bucket := &res.HistogramData.Buckets[i]
+			datum, _, err := sqlbase.DecodeTableKey(&a, typ, bucket.UpperBound, encoding.Ascending)
+			if err != nil {
+				return nil, err
+			}
+			res.Histogram[i] = cat.HistogramBucket{
+				NumEq:         float64(bucket.NumEq),
+				NumRange:      float64(bucket.NumRange),
+				DistinctRange: bucket.DistinctRange,
+				UpperBound:    datum,
+			}
+		}
 	}
 
-	return tableStatistic, nil
+	return res, nil
 }
 
 // getTableStatsFromDB retrieves the statistics in system.table_statistics

pkg/sql/stats/stats_cache_test.go

@@ -34,7 +34,7 @@ import (
 )
 
 func insertTableStat(
-	ctx context.Context, db *client.DB, ex sqlutil.InternalExecutor, stat *TableStatistic,
+	ctx context.Context, db *client.DB, ex sqlutil.InternalExecutor, stat *TableStatisticProto,
 ) error {
 	insertStatStmt := `
 INSERT INTO system.table_statistics ("tableID", "statisticID", name, "columnIDs", "createdAt",
@@ -62,8 +62,8 @@ VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
 	if len(stat.Name) != 0 {
 		args[2] = stat.Name
 	}
-	if stat.Histogram != nil {
-		histogramBytes, err := protoutil.Marshal(stat.Histogram)
+	if stat.HistogramData != nil {
+		histogramBytes, err := protoutil.Marshal(stat.HistogramData)
 		if err != nil {
 			return err
 		}
@@ -94,7 +94,10 @@ func lookupTableStats(
 }
 
 func checkStatsForTable(
-	ctx context.Context, sc *TableStatisticsCache, expected []*TableStatistic, tableID sqlbase.ID,
+	ctx context.Context,
+	sc *TableStatisticsCache,
+	expected []*TableStatisticProto,
+	tableID sqlbase.ID,
 ) error {
 	// Initially the stats won't be in the cache.
 	if statsList, ok := lookupTableStats(ctx, sc, tableID); ok {
@@ -107,7 +110,7 @@ func checkStatsForTable(
 	if err != nil {
 		return errors.Errorf(err.Error())
 	}
-	if !reflect.DeepEqual(statsList, expected) {
+	if !checkStats(statsList, expected) {
 		return errors.Errorf("for lookup of key %d, expected stats %s, got %s", tableID, expected, statsList)
 	}
 
@@ -118,12 +121,24 @@ func checkStatsForTable(
 	return nil
 }
 
+func checkStats(actual []*TableStatistic, expected []*TableStatisticProto) bool {
+	if len(actual) == 0 && len(expected) == 0 {
+		// DeepEqual differentiates between nil and empty slices, we don't.
+		return true
+	}
+	var protoList []*TableStatisticProto
+	for i := range actual {
+		protoList = append(protoList, &actual[i].TableStatisticProto)
+	}
+	return reflect.DeepEqual(protoList, expected)
+}
+
 func initTestData(
 	ctx context.Context, db *client.DB, ex sqlutil.InternalExecutor,
-) (map[sqlbase.ID][]*TableStatistic, error) {
+) (map[sqlbase.ID][]*TableStatisticProto, error) {
 	// The expected stats must be ordered by TableID+, CreatedAt- so they can
 	// later be compared with the returned stats using reflect.DeepEqual.
-	expStatsList := []TableStatistic{
+	expStatsList := []TableStatisticProto{
 		{
 			TableID:       sqlbase.ID(100),
 			StatisticID:   0,
@@ -133,7 +148,7 @@ func initTestData(
 			RowCount:      32,
 			DistinctCount: 30,
 			NullCount:     0,
-			Histogram: &HistogramData{ColumnType: *types.Int, Buckets: []HistogramData_Bucket{
+			HistogramData: &HistogramData{ColumnType: *types.Int, Buckets: []HistogramData_Bucket{
 				{NumEq: 3, NumRange: 30, UpperBound: encoding.EncodeVarintAscending(nil, 3000)}},
 			},
 		},
@@ -169,7 +184,7 @@ func initTestData(
 
 	// Insert the stats into system.table_statistics
 	// and store them in maps for fast retrieval.
-	expectedStats := make(map[sqlbase.ID][]*TableStatistic)
+	expectedStats := make(map[sqlbase.ID][]*TableStatisticProto)
 	for i := range expStatsList {
 		stat := &expStatsList[i]
 
@@ -284,7 +299,7 @@ func TestCacheWait(t *testing.T) {
 				stats, err := sc.GetTableStats(ctx, id)
 				if err != nil {
 					t.Error(err)
-				} else if !reflect.DeepEqual(stats, expectedStats[id]) {
+				} else if !checkStats(stats, expectedStats[id]) {
 					t.Errorf("for table %d, expected stats %s, got %s", id, expectedStats[id], stats)
 				}
 				wg.Done()