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Change inv_truncate() to not repeat its systable_getnext_ordered() scan.

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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.
This commit is contained in:
Tom Lane 2011-01-26 19:33:50 -05:00
parent 8b6f5f2510
commit 7ab6f2da23
1 changed files with 16 additions and 5 deletions
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21
src/backend/storage/large_object/inv_api.c
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@ -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);