Merge pull request #1935 from ecordell/spanner-now-stale

spanner: use stale reads for current_timestamp for optimized revision
authzed · Jun 11, 2024 · 4434d80 · 4434d80
2 parents 2611fcb + 2b77bad
commit 4434d80
Show file tree

Hide file tree

Showing 4 changed files with 22 additions and 17 deletions.
diff --git a/internal/datastore/spanner/options.go b/internal/datastore/spanner/options.go
@@ -113,7 +113,7 @@ func RevisionQuantization(bucketSize time.Duration) Option {
 	}
 }
 
-// FollowerReadDelay is the time delay to apply to enable historial reads.
+// FollowerReadDelay is the time delay to apply to enable historical reads.
 //
 // This value defaults to 0 seconds.
 func FollowerReadDelay(delay time.Duration) Option {

diff --git a/internal/datastore/spanner/revisions.go b/internal/datastore/spanner/revisions.go
@@ -11,28 +11,27 @@ import (
 	"github.com/authzed/spicedb/pkg/datastore"
 )
 
-var ParseRevisionString = revisions.RevisionParser(revisions.Timestamp)
+var (
+	ParseRevisionString = revisions.RevisionParser(revisions.Timestamp)
+	nowStmt             = spanner.NewStatement("SELECT CURRENT_TIMESTAMP()")
+)
 
-func (sd *spannerDatastore) headRevisionInternal(ctx context.Context) (datastore.Revision, error) {
-	now, err := sd.now(ctx)
-	if err != nil {
+func (sd *spannerDatastore) HeadRevision(ctx context.Context) (datastore.Revision, error) {
+	var timestamp time.Time
+	if err := sd.client.Single().Query(ctx, nowStmt).Do(func(r *spanner.Row) error {
+		return r.Columns(&timestamp)
+	}); err != nil {
 		return datastore.NoRevision, fmt.Errorf(errRevision, err)
 	}
-
-	return revisions.NewForTime(now), nil
+	return revisions.NewForTime(timestamp), nil
 }
 
-func (sd *spannerDatastore) HeadRevision(ctx context.Context) (datastore.Revision, error) {
-	return sd.headRevisionInternal(ctx)
-}
-
-func (sd *spannerDatastore) now(ctx context.Context) (time.Time, error) {
+func (sd *spannerDatastore) staleHeadRevision(ctx context.Context) (datastore.Revision, error) {
 	var timestamp time.Time
-	if err := sd.client.Single().Query(ctx, spanner.NewStatement("SELECT CURRENT_TIMESTAMP()")).Do(func(r *spanner.Row) error {
+	if err := sd.client.Single().WithTimestampBound(spanner.ExactStaleness(sd.config.followerReadDelay)).Query(ctx, nowStmt).Do(func(r *spanner.Row) error {
 		return r.Columns(&timestamp)
 	}); err != nil {
-		return time.Time{}, err
+		return datastore.NoRevision, fmt.Errorf(errRevision, err)
 	}
-
-	return timestamp, nil
+	return revisions.NewForTime(timestamp), nil
 }
diff --git a/internal/datastore/spanner/spanner.go b/internal/datastore/spanner/spanner.go
@@ -175,7 +175,11 @@ func NewSpannerDatastore(ctx context.Context, database string, opts ...Option) (
 		cachedEstimatedBytesPerRelationshipLock: sync.RWMutex{},
 		tableSizesStatsTable:                    tableSizesStatsTable,
 	}
-	ds.RemoteClockRevisions.SetNowFunc(ds.headRevisionInternal)
+	// Optimized revision and revision checking use a stale read for the
+	// current timestamp.
+	// TODO: Still investigating whether a stale read can be used for
+	//       HeadRevision for FullConsistency queries.
+	ds.RemoteClockRevisions.SetNowFunc(ds.staleHeadRevision)
 
 	return ds, nil
 }

diff --git a/tools/analyzers/go.work.sum b/tools/analyzers/go.work.sum
@@ -1572,6 +1572,8 @@ github.com/pierrec/lz4/v4 v4.1.17 h1:kV4Ip+/hUBC+8T6+2EgburRtkE9ef4nbY3f4dFhGjMc
 github.com/pierrec/lz4/v4 v4.1.17/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/pierrec/lz4/v4 v4.1.18 h1:xaKrnTkyoqfh1YItXl56+6KJNVYWlEEPuAQW9xsplYQ=
 github.com/pierrec/lz4/v4 v4.1.18/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
+github.com/pierrec/lz4/v4 v4.1.21 h1:yOVMLb6qSIDP67pl/5F7RepeKYu/VmTyEXvuMI5d9mQ=
+github.com/pierrec/lz4/v4 v4.1.21/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e h1:aoZm08cpOy4WuID//EZDgcC4zIxODThtZNPirFr42+A=
 github.com/pkg/sftp v1.13.1 h1:I2qBYMChEhIjOgazfJmV3/mZM256btk6wkCDRmW7JYs=
 github.com/pkg/sftp v1.13.6 h1:JFZT4XbOU7l77xGSpOdW+pwIMqP044IyjXX6FGyEKFo=