Hi Michael On Mon, Oct 2, 2017 at 6:48 PM, Michael Paquier <michael.paqu...@gmail.com> wrote: > > Jacob, here are some ideas to make this thread move on. I would > suggest to produce a set of patches that do things incrementally: > 1) One patch that changes the calls of PageGetLSN to > BufferGetLSNAtomic which are now not appropriate. You have spotted > some of them in the btree and gist code, but not all based on my first > lookup. There is still one in gistFindCorrectParent and one in btree > _bt_split. The monitoring of the other calls (sequence.c and > vacuumlazy.c) looked safe. There is another one in XLogRecordAssemble > that should be fixed I think.
Thank you for your suggestions. Please find the first patch attached as "0001-...". We verified both, gistFindCorrectParent and _bt_split and all calls to PageGetLSN are made with exclusive lock on the buffer contents held. > 2) A second patch that strengthens a bit checks around > BufferGetLSNAtomic. One idea would be to use LWLockHeldByMe, as you > are originally suggesting. > A comment could be as well added in bufpage.h for PageGetLSN to let > users know that it should be used carefully, in the vein of what is > mentioned in src/backend/access/transam/README. The second patch "0002-..." does the above. We have a comment added to AssertPageIsLockedForLSN as suggested. The assertion added caught at least one code path where TestForOldSnapshot calls PageGetLSN without holding any lock. The snapshot_too_old test in "check-world" failed due to the assertion failure. This needs to be fixed, see the open question in the opening mail on this thread. Asim and Jacob
0001-Change-incorrect-calls-to-PageGetLSN-to-BufferGetLSN.patch
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0002-PageGetLSN-assert-that-locks-are-properly-held.patch
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