core/rawdb: fix the transaction indexer (#22395)

core/rawdb/chain_iterator.go

@@ -243,14 +243,14 @@ func indexTransactions(db ethdb.Database, from uint64, to uint64, interrupt chan
 			}
 		}
 	}
-	// If there exists uncommitted data, flush them.
-	if batch.ValueSize() > 0 {
-		WriteTxIndexTail(batch, lastNum) // Also write the tail there
+	// Flush the new indexing tail and the last committed data. It can also happen
+	// that the last batch is empty because nothing to index, but the tail has to
+	// be flushed anyway.
+	WriteTxIndexTail(batch, lastNum)
 	if err := batch.Write(); err != nil {
 		log.Crit("Failed writing batch to db", "error", err)
 		return
 	}
-	}
 	select {
 	case <-interrupt:
 		log.Debug("Transaction indexing interrupted", "blocks", blocks, "txs", txs, "tail", lastNum, "elapsed", common.PrettyDuration(time.Since(start)))
@@ -334,14 +334,14 @@ func unindexTransactions(db ethdb.Database, from uint64, to uint64, interrupt ch
 			}
 		}
 	}
-	// Commit the last batch if there exists uncommitted data
-	if batch.ValueSize() > 0 {
+	// Flush the new indexing tail and the last committed data. It can also happen
+	// that the last batch is empty because nothing to unindex, but the tail has to
+	// be flushed anyway.
 	WriteTxIndexTail(batch, nextNum)
 	if err := batch.Write(); err != nil {
 		log.Crit("Failed writing batch to db", "error", err)
 		return
 	}
-	}
 	select {
 	case <-interrupt:
 		log.Debug("Transaction unindexing interrupted", "blocks", blocks, "txs", txs, "tail", to, "elapsed", common.PrettyDuration(time.Since(start)))