Skip second WriteToc() call for custom-format dumps without data.

Presently, "pg_dump --format=custom" calls WriteToc() twice.  The
second call updates the data offset information, which allegedly
makes parallel pg_restore significantly faster.  However, if we're
not dumping any data, there are no data offsets to update, so we
can skip this step.

Reviewed-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://postgr.es/m/Z9c1rbzZegYQTOQE%40nathan

diff --git a/src/bin/pg_dump/pg_backup_custom.c b/src/bin/pg_dump/pg_backup_custom.c
index e44b887eb29bdbec2b5c8cce51dec98da303dc94..f7c3af56304ce3116a1f5862e4ebb6c14cebd205 100644 (file)
--- a/src/bin/pg_dump/pg_backup_custom.c
+++ b/src/bin/pg_dump/pg_backup_custom.c
@@ -755,9 +755,11 @@ _CloseArchive(ArchiveHandle *AH)
                 * If possible, re-write the TOC in order to update the data offset
                 * information.  This is not essential, as pg_restore can cope in most
                 * cases without it; but it can make pg_restore significantly faster
-                * in some situations (especially parallel restore).
+                * in some situations (especially parallel restore).  We can skip this
+                * step if we're not dumping any data; there are no offsets to update
+                * in that case.
                 */
-               if (ctx->hasSeek &&
+               if (ctx->hasSeek && AH->public.dopt->dumpData &&
                        fseeko(AH->FH, tpos, SEEK_SET) == 0)
                        WriteToc(AH);
        }