| Hi, Jim.
Thanks for review.
On 5/1/15 11:19 AM, Vladimir Borodin wrote: There are situations in which vacuuming big btree index causes stuck in
WAL replaying on hot standby servers for quite a long time. I’ve
described the problem in more details in this thread [0]. Below in that
thread Kevin Grittner proposed a good way for improving btree scans so
that btree vacuuming logic could be seriously simplified. Since I don’t
know when that may happen I’ve done a patch that makes some improvement
right now. If Kevin or someone else would expand [1] for handling all
types of btree scans, I suppose, my patch could be thrown away and
vacuuming logic should be strongly rewritten.
This looks like a good way to address this until the more significant work can be done. I'm not a fan of "RBM_ZERO_NO_BM_VALID"; how about RBM_ZERO_BM_INVALID? or BM_NOT_VALID? Or maybe I'm just trying to impose too much English on the code; I see the logic to NO_BM_VALID…
Perhaps, RBM_ZERO_NO_BM_VALID is not so good (it makes more difficult to grep BM_VALID in code), but I don’t actually like BM_INVALID and BM_NOT_VALID, sorry :( But I also don’t insist on NO_BM_VALID, any other suggestions?
+ * RBM_ZERO_NO_BM_VALID is the same as RBM_ZERO_AND_LOCK, but does not set
+ * BM_VALID bit before returning buffer so that noone could pin it.
It would be better to explain why we want that mode. How about:
RBM_ZERO_NO_BM_VALID is the same as RBM_ZERO_AND_LOCK but does not set BM_VALID before returning the buffer. This is done to ensure that no one can pin the buffer without actually reading the buffer contents in. This is necessary while replying XLOG_BTREE_VACUUM records in hot standby.
Good point, fixed in attached patch.
+ if (mode == RBM_ZERO_NO_BM_VALID)
+ TerminateBufferIO(bufHdr, false, 0);
+ else
+ TerminateBufferIO(bufHdr, false, BM_VALID);
Simply passing in a 0 seems a bit odd to me; is there anywhere else we do that?
Yes, it is done the same way in FlushBuffer function [0]. Also comments before TerminateBufferIO say that 0 is expected value for third argument.
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btree_vacuum_v2.patch
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-- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com
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May the force be with you…
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