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Prevent GIN deleted pages from being reclaimed too early

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When GIN vacuum deletes a posting tree page, it assumes that no concurrent
searchers can access it, thanks to ginStepRight() locking two pages at once.
However, since 9.4 searches can skip parts of posting trees descending from the
root.  That leads to the risk that page is deleted and reclaimed before
concurrent search can access it.

This commit prevents the risk of above by waiting for every transaction, which
might wait to reference this page, to finish.  Due to binary compatibility
we can't change GinPageOpaqueData to store corresponding transaction id.
Instead we reuse page header pd_prune_xid field, which is unused in index pages.

Discussion: https://postgr.es/m/31a702a.14dd.166c1366ac1.Coremail.chjischj%40163.com
Author: Andrey Borodin, Alexander Korotkov
Reviewed-by: Alexander Korotkov
Backpatch-through: 9.4
This commit is contained in:
Alexander Korotkov
2018-12-13 06:12:31 +03:00
parent c6ade7a8cd
commit 52ac6cd2d0
6 changed files with 22 additions and 13 deletions
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7
src/backend/access/gin/ginutil.c
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@ -309,12 +309,7 @@ GinNewBuffer(Relation index)
*/
if (ConditionalLockBuffer(buffer))
{
Page page = BufferGetPage(buffer);
if (PageIsNew(page))
return buffer; /* OK to use, if never initialized */
if (GinPageIsDeleted(page))
if (GinPageIsRecyclable(BufferGetPage(buffer)))
return buffer; /* OK to use */
LockBuffer(buffer, GIN_UNLOCK);