diff --git a/pkg/ccl/backupccl/backup_processor.go b/pkg/ccl/backupccl/backup_processor.go
index 625e28900b19..0c6e1cd43509 100644
--- a/pkg/ccl/backupccl/backup_processor.go
+++ b/pkg/ccl/backupccl/backup_processor.go
@@ -12,6 +12,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"sort"
 	"time"
 
 	"github.com/cockroachdb/cockroach/pkg/base"
@@ -79,8 +80,18 @@ var (
 		16<<20,
 		settings.NonNegativeInt,
 	)
+	smallFileBuffer = settings.RegisterByteSizeSetting(
+		"bulkio.backup.merge_file_buffer_size",
+		"size limit used when buffering backup files before merging them",
+		16<<20,
+		settings.NonNegativeInt,
+	)
 )
 
+// maxSinkQueueFiles is how many replies we'll queue up before flushing to allow
+// some re-ordering, unless we hit smallFileBuffer size first.
+const maxSinkQueueFiles = 24
+
 const backupProcessorName = "backupDataProcessor"
 
 // TODO(pbardea): It would be nice if we could add some DistSQL processor tests
@@ -444,6 +455,7 @@ func runBackupProcessor(
 			enc:            spec.Encryption,
 			targetFileSize: targetFileSize,
 			progCh:         progCh,
+			settings:       &flowCtx.Cfg.Settings.SV,
 		}
 
 		defaultStore, err := flowCtx.Cfg.ExternalStorage(ctx, defaultConf)
@@ -486,7 +498,7 @@ func runBackupProcessor(
 				sink = defaultSink
 			}
 
-			if err := sink.write(ctx, res); err != nil {
+			if err := sink.push(ctx, res); err != nil {
 				return err
 			}
 		}
@@ -507,12 +519,16 @@ type sstSinkConf struct {
 	targetFileSize int64
 	enc            *roachpb.FileEncryptionOptions
 	id             base.SQLInstanceID
+	settings       *settings.Values
 }
 
 type sstSink struct {
 	dest cloud.ExternalStorage
 	conf sstSinkConf
 
+	queue     []returnedSST
+	queueSize int
+
 	sst     storage.SSTWriter
 	ctx     context.Context
 	cancel  func()
@@ -520,11 +536,24 @@ type sstSink struct {
 	outName string
 
 	flushedFiles    []BackupManifest_File
+	flushedSize     int64
 	flushedRevStart hlc.Timestamp
 	completedSpans  int32
+
+	stats struct {
+		files       int
+		flushes     int
+		oooFlushes  int
+		sizeFlushes int
+		spanGrows   int
+	}
 }
 
 func (s *sstSink) Close() error {
+	if log.V(1) && s.ctx != nil {
+		log.Infof(s.ctx, "backup sst sink recv'd %d files, wrote %d (%d due to size, %d due to re-ordering), %d recv files extended prior span",
+			s.stats.files, s.stats.flushes, s.stats.sizeFlushes, s.stats.oooFlushes, s.stats.spanGrows)
+	}
 	if s.cancel != nil {
 		s.cancel()
 	}
@@ -534,10 +563,54 @@ func (s *sstSink) Close() error {
 	return nil
 }
 
+// push pushes one returned backup file into the sink. Returned files can arrive
+// out of order, but must be written to an underlying file in-order or else a
+// new underlying file has to be opened. The queue allows buffering up files and
+// sorting them before pushing them to the underlying file to try to avoid this.
+// When the queue length or sum of the data sizes in it exceeds thresholds the
+// queue is sorted and the first half is flushed.
+func (s *sstSink) push(ctx context.Context, resp returnedSST) error {
+	s.queue = append(s.queue, resp)
+	s.queueSize += len(resp.sst)
+
+	if len(s.queue) >= maxSinkQueueFiles || s.queueSize >= int(smallFileBuffer.Get(s.conf.settings)) {
+		sort.Slice(s.queue, func(i, j int) bool { return s.queue[i].f.Span.Key.Compare(s.queue[j].f.Span.Key) < 0 })
+
+		// Drain the first half.
+		drain := len(s.queue) / 2
+		if drain < 1 {
+			drain = 1
+		}
+		for i := range s.queue[:drain] {
+			if err := s.write(ctx, s.queue[i]); err != nil {
+				return err
+			}
+			s.queueSize -= len(s.queue[i].sst)
+		}
+
+		// Shift down the remainder of the queue and slice off the tail.
+		copy(s.queue, s.queue[drain:])
+		s.queue = s.queue[:len(s.queue)-drain]
+	}
+	return nil
+}
+
 func (s *sstSink) flush(ctx context.Context) error {
+	for i := range s.queue {
+		if err := s.write(ctx, s.queue[i]); err != nil {
+			return err
+		}
+	}
+	s.queue = nil
+	return s.flushFile(ctx)
+}
+
+func (s *sstSink) flushFile(ctx context.Context) error {
 	if s.out == nil {
 		return nil
 	}
+	s.stats.flushes++
+
 	if err := s.sst.Finish(); err != nil {
 		return err
 	}
@@ -565,6 +638,7 @@ func (s *sstSink) flush(ctx context.Context) error {
 	}
 
 	s.flushedFiles = nil
+	s.flushedSize = 0
 	s.flushedRevStart.Reset()
 	s.completedSpans = 0
 
@@ -593,14 +667,15 @@ func (s *sstSink) open(ctx context.Context) error {
 }
 
 func (s *sstSink) write(ctx context.Context, resp returnedSST) error {
+	s.stats.files++
+
 	span := resp.f.Span
 
 	// If this span starts before the last buffered span ended, we need to flush
 	// since it overlaps but SSTWriter demands writes in-order.
-	// TODO(dt): consider buffering resp until _next_ `write` to allow minimal
-	// reordering of writes to avoid extra flushes.
 	if len(s.flushedFiles) > 0 && span.Key.Compare(s.flushedFiles[len(s.flushedFiles)-1].Span.EndKey) < 0 {
-		if err := s.flush(ctx); err != nil {
+		s.stats.oooFlushes++
+		if err := s.flushFile(ctx); err != nil {
 			return err
 		}
 	}
@@ -648,6 +723,7 @@ func (s *sstSink) write(ctx context.Context, resp returnedSST) error {
 		s.flushedFiles[l].StartTime.EqOrdering(resp.f.StartTime) {
 		s.flushedFiles[l].Span.EndKey = span.EndKey
 		s.flushedFiles[l].EntryCounts.add(resp.f.EntryCounts)
+		s.stats.spanGrows++
 	} else {
 		f := resp.f
 		f.Path = s.outName
@@ -655,11 +731,12 @@ func (s *sstSink) write(ctx context.Context, resp returnedSST) error {
 	}
 	s.flushedRevStart.Forward(resp.revStart)
 	s.completedSpans += resp.completedSpans
+	s.flushedSize += int64(len(resp.sst))
 
 	// If our accumulated SST is now big enough, flush it.
-	// TODO(dt): use the compressed size instead.
-	if s.sst.DataSize > s.conf.targetFileSize {
-		if err := s.flush(ctx); err != nil {
+	if s.flushedSize > s.conf.targetFileSize {
+		s.stats.sizeFlushes++
+		if err := s.flushFile(ctx); err != nil {
 			return err
 		}
 	}