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Add some notes about why it's not a bug that RI_FKey_check calls

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HeapTupleSatisfiesItself without doing LockBuffer first.  This code
is a bit fragile, but AFAICS it's not actually broken.
This commit is contained in:
Tom Lane 2006-08-27 21:41:21 +00:00
parent e06fda0a8b
commit 7a2fe85b03
1 changed files with 14 additions and 4 deletions
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18
src/backend/utils/adt/ri_triggers.c
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@ -17,7 +17,7 @@
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
*
* $PostgreSQL: pgsql/src/backend/utils/adt/ri_triggers.c,v 1.87 2006/08/21 19:15:29 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/ri_triggers.c,v 1.88 2006/08/27 21:41:21 tgl Exp $
*
* ----------
*/
@ -212,9 +212,19 @@ RI_FKey_check(PG_FUNCTION_ARGS)
}
/*
* We should not even consider checking the row if it is no longer valid
* since it was either deleted (doesn't matter) or updated (in which case
* it'll be checked with its final values).
* We should not even consider checking the row if it is no longer valid,
* since it was either deleted (so the deferred check should be skipped)
* or updated (in which case only the latest version of the row should
* be checked). Test its liveness with HeapTupleSatisfiesItself.
*
* NOTE: The normal coding rule is that one must acquire the buffer
* content lock to call HeapTupleSatisfiesFOO. We can skip that here
* because we know that AfterTriggerExecute just fetched the tuple
* successfully, so there cannot be a VACUUM compaction in progress
* on the page (either heap_fetch would have waited for the VACUUM,
* or the VACUUM's LockBufferForCleanup would be waiting for us to drop
* pin). And since this is a row inserted by our open transaction,
* no one else can be entitled to change its xmin/xmax.
*/
Assert(new_row_buf != InvalidBuffer);
if (!HeapTupleSatisfiesItself(new_row->t_data, new_row_buf))