diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 0d92e694d6a..6ac4909794a 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -9,8 +9,12 @@
  * In a parallel vacuum, we perform both index bulk deletion and index cleanup
  * with parallel worker processes.  Individual indexes are processed by one
  * vacuum process.  ParallelVacuumState contains shared information as well as
- * the memory space for storing dead items allocated in the DSA area.  We
- * launch parallel worker processes at the start of parallel index
+ * the memory space for storing dead items allocated in the DSA area. Furthemore
+ * the primary statistical information about indexes gathered during vacuuming
+ * is stored in the IndexBulkDeleteResult structure. In addition, the buffer and
+ * WAL statistics for indexes processed by parallel workers are stored in the
+ * buffer_usage and wal_usage fields of the ParallelVacuumState.
+ * We launch parallel worker processes at the start of parallel index
  * bulk-deletion and index cleanup and once all indexes are processed, the
  * parallel worker processes exit.  Each time we process indexes in parallel,
  * the parallel context is re-initialized so that the same DSM can be used for