| From: | Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: the big picture for index-only scans |
| Date: | 2011-08-19 18:01:00 |
| Message-ID: | CAHMh4-ZeSXcFFeseFO9nAeL_25CjAUZnfvtoR7-0QUCBZ4iL-g@mail.gmail.com |
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| Lists: | pgsql-hackers |
>
>
> Well, that would certainly be alarming if true, but I don't think it
> is. As far as I can see, the overhead of making the visibility map
> crash-safe is just (1) a very small percentage increase in the work
> being done by VACUUM and (2) a slight possibility of extra work done
> by a foreground process if the visibility map bit changes at almost
> exactly the same time the process was about to insert, update, or
> delete a tuple.
>
> Let's forget the overhead posed by vacuum. Can you please point me to the
design which talks in detail of the second overhead?
Thanks.
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| Previous Message | Sergey E. Koposov | 2011-08-19 17:56:06 | two index bitmap scan of a big table & hash_seq_search |