Index only scans and visibilitymap.c

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Index only scans and visibilitymap.c
Date: 2011-10-23 22:41:05
Message-ID: CAMkU=1wo4Od9Xc5-C4Yojx-5Z+ps-dgD28pja=DcYdwqxm8Wsw@mail.gmail.com
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With index only scans, the comments in
src/backend/access/heap/visibilitymap.c are probably out of date,
starting with:

"Currently, the visibility map is only used as a hint"

Also, is there a discussion of how and why index-only scans is safe?
i.e. what lock, if any, has to be held while nodeIndexonlyscan.c
calls visibilitymap_test? Do index-only scans need a README file?

Thanks,

Jeff

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