From: | Noah Misch <noah(at)leadboat(dot)com> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Torn page hazard in ginRedoUpdateMetapage() |
Date: | 2012-04-30 17:34:24 |
Message-ID: | 20120430173424.GB14212@tornado.leadboat.com |
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Lists: | pgsql-hackers |
When GIN changes a metapage, we WAL-log its ex-header content and never use a
backup block. This reduces WAL volume since the vast majority of the metapage
is unused. However, ginRedoUpdateMetapage() only restores the WAL-logged
content if the metapage LSN predates the WAL record LSN. If a metapage write
tore and updated the LSN but not the other content, we would fail to complete
the update. Instead, unconditionally reinitialize the metapage similar to how
_bt_restore_meta() handles the situation.
I found this problem by code reading and did not attempt to build a test case
illustrating its practical consequences. It's possible that there's no
problem in practice on account of some reason I haven't contemplated.
Thanks,
nm
Attachment | Content-Type | Size |
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gin-xlog-metapage-v1.patch | text/plain | 926 bytes |
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