From 7ab6f2da23516e48174f3f144ee9ef19bdc287fb Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 26 Jan 2011 19:33:50 -0500 Subject: [PATCH] Change inv_truncate() to not repeat its systable_getnext_ordered() scan. In the case where the initial call of systable_getnext_ordered() returned NULL, this function would nonetheless call it again. That's undefined behavior that only by chance failed to not give visibly incorrect results. Put an if-test around the final loop to prevent that, and in passing improve some comments. No back-patch since there's no actual failure. Per report from YAMAMOTO Takashi. --- src/backend/storage/large_object/inv_api.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/src/backend/storage/large_object/inv_api.c b/src/backend/storage/large_object/inv_api.c index f06bf650756..01e3492cb83 100644 --- a/src/backend/storage/large_object/inv_api.c +++ b/src/backend/storage/large_object/inv_api.c @@ -762,6 +762,9 @@ inv_truncate(LargeObjectDesc *obj_desc, int len) indstate = CatalogOpenIndexes(lo_heap_r); + /* + * Set up to find all pages with desired loid and pageno >= target + */ ScanKeyInit(&skey[0], Anum_pg_largeobject_loid, BTEqualStrategyNumber, F_OIDEQ, @@ -841,10 +844,14 @@ inv_truncate(LargeObjectDesc *obj_desc, int len) { /* * If the first page we found was after the truncation point, we're in - * a hole that we'll fill, but we need to delete the later page. + * a hole that we'll fill, but we need to delete the later page because + * the loop below won't visit it again. */ - if (olddata != NULL && olddata->pageno > pageno) + if (olddata != NULL) + { + Assert(olddata->pageno > pageno); simple_heap_delete(lo_heap_r, &oldtuple->t_self); + } /* * Write a brand new page. @@ -873,11 +880,15 @@ inv_truncate(LargeObjectDesc *obj_desc, int len) } /* - * Delete any pages after the truncation point + * Delete any pages after the truncation point. If the initial search + * didn't find a page, then of course there's nothing more to do. */ - while ((oldtuple = systable_getnext_ordered(sd, ForwardScanDirection)) != NULL) + if (olddata != NULL) { - simple_heap_delete(lo_heap_r, &oldtuple->t_self); + while ((oldtuple = systable_getnext_ordered(sd, ForwardScanDirection)) != NULL) + { + simple_heap_delete(lo_heap_r, &oldtuple->t_self); + } } systable_endscan_ordered(sd);