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Fix incorrect comment in SetBufferCommitInfoNeedsSave().

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Noah Misch spotted the fact that the old comment is in fact incorrect, due
to memory ordering hazards.
This commit is contained in:
Robert Haas 2012-04-18 10:55:40 -04:00
parent e93c0b820f
commit ab77b2da8b
1 changed files with 5 additions and 3 deletions
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8
src/backend/storage/buffer/bufmgr.c
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@ -2376,9 +2376,11 @@ SetBufferCommitInfoNeedsSave(Buffer buffer)
* making the first scan after commit of an xact that added/deleted many
* tuples. So, be as quick as we can if the buffer is already dirty. We
* do this by not acquiring spinlock if it looks like the status bits are
* already OK. (Note it is okay if someone else clears BM_JUST_DIRTIED
* immediately after we look, because the buffer content update is already
* done and will be reflected in the I/O.)
* already. Since we make this test unlocked, there's a chance we might
* fail to notice that the flags have just been cleared, and failed to reset
* them, due to memory-ordering issues. But since this function is only
* intended to be used in cases where failing to write out the data would
* be harmless anyway, it doesn't really matter.
*/
if ((bufHdr->flags & (BM_DIRTY | BM_JUST_DIRTIED)) !=
(BM_DIRTY | BM_JUST_DIRTIED))