rowexec: manually flush progress when backfiling vector indexes

Previously, the vector index codepath in backfill took no special action
to update progress tracking. Since progress tracking uses BulkAdder
flushes to determine when to flush progress and vector indexes don't
currently use BulkAdders during backfill, this meant that vector index
build status never got updated.

This patch adds a manual flush of status whenever an IndexBatch
containing a vector index completes. Vector index inserts are pretty
slow and IndexBatches are pretty large, so this is unlikely to lead to too
many flushes.

Fixes: #146691
Release note (bug fix): Vector index backfill will now properly track job
progress in SHOW JOBS output.

Author: mw5h

pkg/sql/rowexec/indexbackfiller.go

@@ -342,6 +342,7 @@ func (ib *indexBackfiller) ingestIndexEntries(
 
 		var vectorInputEntry rowenc.IndexEntry
 		for indexBatch := range indexEntryCh {
+			addedToVectorIndex := false
 			for _, indexEntry := range indexBatch.indexEntries {
 				// Pace the admission control before processing each index entry.
 				if err := pacer.Pace(ctx); err != nil {
@@ -359,6 +360,7 @@ func (ib *indexBackfiller) ingestIndexEntries(
 					if err != nil {
 						return ib.wrapDupError(ctx, err)
 					} else if isVectorIndex {
+						addedToVectorIndex = true
 						continue
 					}
 				}
@@ -374,6 +376,12 @@ func (ib *indexBackfiller) ingestIndexEntries(
 			mu.Lock()
 			mu.addedSpans = append(mu.addedSpans, indexBatch.completedSpan)
 			mu.Unlock()
+			// Vector indexes don't add to the bulk adder and take a long time to add
+			// entries, so flush progress manually after every indexBatch is processed
+			// that contained vector index entries.
+			if addedToVectorIndex {
+				flushAddedSpans(kvpb.BulkOpSummary{})
+			}
 
 			// After the index KVs have been copied to the underlying BulkAdder, we can
 			// free the memory which was accounted when building the index entries of the
@@ -404,14 +412,6 @@ func (ib *indexBackfiller) ingestIndexEntries(
 	if err := g.Wait(); err != nil {
 		return err
 	}
-
-	// If there are only vector indexes, we push the completed spans manually so that
-	// progress reporting works.
-	// TODO(mw5h): this is a hack to get progress reporting to work for vector only
-	// backfills. We should remove this once we have a more permanent solution.
-	if ib.VectorOnly {
-		flushAddedSpans(kvpb.BulkOpSummary{})
-	}
 	if err := adder.Flush(ctx); err != nil {
 		return ib.wrapDupError(ctx, err)
 	}