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[DNM] sql: pre-split on TRUNCATE #63041

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[DNM] sql: pre-split on TRUNCATE #63041

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38 changes: 36 additions & 2 deletions pkg/sql/drop_table.go
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ import (
"context"
"fmt"
"strings"
"time"

"github.com/cockroachdb/cockroach/pkg/jobs"
"github.com/cockroachdb/cockroach/pkg/jobs/jobspb"
Expand Down Expand Up @@ -388,7 +389,11 @@ func (p *planner) dropTableImpl(
}

// unsplitRangesForTable unsplit any manually split ranges within the table span.
func (p *planner) unsplitRangesForTable(ctx context.Context, tableDesc *tabledesc.Mutable) error {
func (p *planner) unsplitRangesForTable(
ctx context.Context,
tableDesc *tabledesc.Mutable,
indexIDMapping map[descpb.IndexID]descpb.IndexID,
) error {
// Gate this on being the system tenant because secondary tenants aren't
// allowed to scan the meta ranges directly.
if p.ExecCfg().Codec.ForSystemTenant() {
Expand All @@ -397,6 +402,7 @@ func (p *planner) unsplitRangesForTable(ctx context.Context, tableDesc *tabledes
if err != nil {
return err
}
var mappedSplitPoints []roachpb.Key
for _, r := range ranges {
var desc roachpb.RangeDescriptor
if err := r.ValueProto(&desc); err != nil {
Expand All @@ -411,6 +417,34 @@ func (p *planner) unsplitRangesForTable(ctx context.Context, tableDesc *tabledes
return err
}
}

rest, tableID, indexID, err := p.ExecCfg().Codec.DecodeIndexPrefix(desc.StartKey.AsRawKey())
if err != nil {
continue
}
if tableID != uint32(tableDesc.GetID()) {
return errors.Errorf("expected table %d, got table ID %d", tableDesc, tableID)
}
mappedID, ok := indexIDMapping[descpb.IndexID(indexID)]
if !ok {
continue
}
indexPrefix := p.ExecCfg().Codec.IndexPrefix(tableID, uint32(mappedID))
mappedSplitPoints = append(mappedSplitPoints, append(indexPrefix, rest...))
}
// Downsample, remap to new table, split.
// TODO(nvanbenschoten): base this on num nodes or something.
newRanges := 64
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if newRanges > len(mappedSplitPoints) {
newRanges = len(mappedSplitPoints)
}
every := float64(len(mappedSplitPoints)) / float64(newRanges)
expTime := p.ExecCfg().Clock.Now().Add(time.Hour.Nanoseconds(), 0)
for i := 0; i < newRanges; i++ {
splitPoint := mappedSplitPoints[int(float64(i)*every)]
if err := p.ExecCfg().DB.SplitAndScatter(ctx, splitPoint, expTime); err != nil {
return err
}
}
}
return nil
Expand Down Expand Up @@ -441,7 +475,7 @@ func (p *planner) initiateDropTable(

// Unsplit all manually split ranges in the table so they can be
// automatically merged by the merge queue.
if err := p.unsplitRangesForTable(ctx, tableDesc); err != nil {
if err := p.unsplitRangesForTable(ctx, tableDesc, nil); err != nil {
return err
}

Expand Down
14 changes: 13 additions & 1 deletion pkg/sql/truncate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import (
"github.com/cockroachdb/cockroach/pkg/kv"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/security"
"github.com/cockroachdb/cockroach/pkg/settings"
"github.com/cockroachdb/cockroach/pkg/sql/catalog"
"github.com/cockroachdb/cockroach/pkg/sql/catalog/descpb"
"github.com/cockroachdb/cockroach/pkg/sql/catalog/tabledesc"
Expand Down Expand Up @@ -169,6 +170,12 @@ func (t *truncateNode) Next(runParams) (bool, error) { return false, nil }
func (t *truncateNode) Values() tree.Datums { return tree.Datums{} }
func (t *truncateNode) Close(context.Context) {}

var replaceSplits = settings.RegisterBoolSetting(
"sql.truncate.replace_splits",
"whether a truncate operation should replace existing split points with new ones",
true,
)

// truncateTable truncates the data of a table in a single transaction. It does
// so by dropping all existing indexes on the table and creating new ones without
// backfilling any data into the new indexes. The old indexes are cleaned up
Expand Down Expand Up @@ -259,9 +266,14 @@ func (p *planner) truncateTable(
return err
}

var replaceSplitsMapping map[descpb.IndexID]descpb.IndexID
if replaceSplits.Get(&p.ExecCfg().Settings.SV) {
replaceSplitsMapping = indexIDMapping
}

// Unsplit all manually split ranges in the table so they can be
// automatically merged by the merge queue.
if err := p.unsplitRangesForTable(ctx, tableDesc); err != nil {
if err := p.unsplitRangesForTable(ctx, tableDesc, replaceSplitsMapping); err != nil {
return err
}

Expand Down