On 9/15/2007 10:37 PM, Tom Lane wrote:
Log Message:
-----------
Fix aboriginal mistake in lazy VACUUM's code for truncating away
no-longer-needed pages at the end of a table. We thought we could throw away
pages containing HEAPTUPLE_DEAD tuples; but this is not so, because such
tuples very likely have index entries pointing at them, and we wouldn't have
removed the index entries. The problem only emerges in a somewhat unlikely
race condition: the dead tuples have to have been inserted by a transaction
that later aborted, and this has to have happened between VACUUM's initial
scan of the page and then rechecking it for empty in count_nondeletable_pages.
But that timespan will include an index-cleaning pass, so it's not all that
hard to hit. This seems to explain a couple of previously unsolved bug
reports.
You mean symptoms like multiple index tuples pointing to the same heap
tuple, thus presenting the same heap tuple twice during an index scan,
don't you?
Jan
Tags:
----
REL8_2_STABLE
Modified Files:
--------------
pgsql/src/backend/commands:
vacuumlazy.c (r1.81.2.2 -> r1.81.2.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c?r1=1.81.2.2&r2=1.81.2.3)
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