On 16.12.2010 16:50, Alvaro Herrera wrote:
Excerpts from Ng, Stan's message of mié dic 15 21:07:57 -0300 2010:
Now I just need to get my head wrapped around the corner cases of MVCC
+ indexes. From a layman's perspective, it seems the index should only
operate on the latest version. Perhaps there's a pgsql configuration
option or hint on the index that I'm missing... The hunt continues!
All tuples need to have index pointers, even the dead ones.
To be precise, tuples that are truly dead, ie. not visible to anyone
anymore, don't need index pointers. They usually have index pointers
anyway, because they were needed to find the tuples before they became
dead. But if you abort a vacuum after it has scanned the indexes, you
end up with dead heap tuples with no index pointers. Also, there's an
optimization in b-tree that removes index pointers to dead tuples, when
they are encountered during index scans.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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