scan_internal: don't visit empty external files

When truncating external files to our scan bounds, we may find that
the file has Start == End. Other validation in ingest asserts these
are invalid bounds.

ingest.go

@@ -1179,23 +1179,6 @@ type ExternalFile struct {
 	Level uint8
 }
 
-func (e *ExternalFile) cloneFromFileMeta(f *fileMetadata) {
-	*e = ExternalFile{
-		Bounds: KeyRange{
-			Start: append([]byte(nil), f.Smallest.UserKey...),
-			End:   append([]byte(nil), f.Largest.UserKey...),
-		},
-		HasPointKey: f.HasPointKeys,
-		HasRangeKey: f.HasRangeKeys,
-		Size:        f.Size,
-	}
-	e.SyntheticSuffix = append([]byte(nil), f.SyntheticSuffix...)
-	if pr := f.PrefixReplacement; pr != nil {
-		e.ContentPrefix = append([]byte(nil), pr.ContentPrefix...)
-		e.SyntheticPrefix = append([]byte(nil), pr.SyntheticPrefix...)
-	}
-}
-
 // IngestWithStats does the same as Ingest, and additionally returns
 // IngestOperationStats.
 func (d *DB) IngestWithStats(paths []string) (IngestOperationStats, error) {

scan_internal.go

@@ -7,6 +7,7 @@ package pebble
 import (
 	"context"
 	"fmt"
+	"slices"
 
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble/internal/base"
@@ -460,27 +461,43 @@ func (d *DB) truncateExternalFile(
 	level int,
 	file *fileMetadata,
 	objMeta objstorage.ObjectMetadata,
-) *ExternalFile {
+) (*ExternalFile, error) {
 	cmp := d.cmp
-	sst := &ExternalFile{}
-	sst.cloneFromFileMeta(file)
-	sst.Level = uint8(level)
-	sst.ObjName = objMeta.Remote.CustomObjectName
-	sst.Locator = objMeta.Remote.Locator
-	needsLowerTruncate := cmp(lower, file.Smallest.UserKey) > 0
-	needsUpperTruncate := cmp(upper, file.Largest.UserKey) < 0 || (cmp(upper, file.Largest.UserKey) == 0 && !file.Largest.IsExclusiveSentinel())
+	sst := &ExternalFile{
+		Level:           uint8(level),
+		ObjName:         objMeta.Remote.CustomObjectName,
+		Locator:         objMeta.Remote.Locator,
+		Bounds:          KeyRange{},
+		HasPointKey:     file.HasPointKeys,
+		HasRangeKey:     file.HasRangeKeys,
+		Size:            file.Size,
+		SyntheticSuffix: slices.Clone(file.SyntheticSuffix),
+	}
+	if pr := file.PrefixReplacement; pr != nil {
+		sst.ContentPrefix = slices.Clone(pr.ContentPrefix)
+		sst.SyntheticPrefix = slices.Clone(pr.SyntheticPrefix)
+	}
 
+	needsLowerTruncate := cmp(lower, file.Smallest.UserKey) > 0
 	if needsLowerTruncate {
-		sst.Bounds.Start = sst.Bounds.Start[:0]
-		sst.Bounds.Start = append(sst.Bounds.Start, lower...)
+		sst.Bounds.Start = slices.Clone(lower)
+	} else {
+		sst.Bounds.Start = slices.Clone(file.Smallest.UserKey)
 	}
 
+	cmpUpper := cmp(upper, file.Largest.UserKey)
+	needsUpperTruncate := cmpUpper < 0 || (cmpUpper == 0 && !file.Largest.IsExclusiveSentinel())
 	if needsUpperTruncate {
-		sst.Bounds.End = sst.Bounds.End[:0]
-		sst.Bounds.End = append(sst.Bounds.End, upper...)
+		sst.Bounds.End = slices.Clone(upper)
+	} else {
+		sst.Bounds.End = slices.Clone(file.Largest.UserKey)
 	}
 
-	return sst
+	if cmp(sst.Bounds.Start, sst.Bounds.End) >= 0 {
+		return nil, errors.AssertionFailedf("pebble: invalid external file bounds after truncation [%q, %q)", sst.Bounds.Start, sst.Bounds.End)
+	}
+
+	return sst, nil
 }
 
 // truncateSharedFile truncates a shared file's [Smallest, Largest] fields to
@@ -693,6 +710,10 @@ func scanInternalImpl(
 		for level := firstLevelWithRemote; level < numLevels; level++ {
 			files := current.Levels[level].Iter()
 			for f := files.SeekGE(cmp, lower); f != nil && cmp(f.Smallest.UserKey, upper) < 0; f = files.Next() {
+				if cmp(lower, f.Largest.UserKey) == 0 && f.Largest.IsExclusiveSentinel() {
+					continue
+				}
+
 				var objMeta objstorage.ObjectMetadata
 				var err error
 				objMeta, err = provider.Lookup(fileTypeTable, f.FileBacking.DiskFileNum)
@@ -737,7 +758,10 @@ func scanInternalImpl(
 						return err
 					}
 				} else if objMeta.IsExternal() {
-					sst := iter.db.truncateExternalFile(ctx, lower, upper, level, f, objMeta)
+					sst, err := iter.db.truncateExternalFile(ctx, lower, upper, level, f, objMeta)
+					if err != nil {
+						return err
+					}
 					if err := opts.visitExternalFile(sst); err != nil {
 						return err
 					}

testdata/ingest_external

@@ -695,3 +695,19 @@ a: (d2-v1, .)
 b: (d1-v1, .)
 d: (d1-v1, .)
 e: (d2-v1, .)
+
+reset
+----
+
+build-remote trunctest
+set a foo
+set b bar
+----
+
+ingest-external
+trunctest bounds=(a,c)
+----
+
+replicate 1 2 c z
+----
+replicated 0 external SSTs