| From: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: lazy vacuum sleeps with exclusive lock on table |
| Date: | 2007-06-29 00:29:09 |
| Message-ID: | 20070629091438.7C11.ITAGAKI.TAKAHIRO@oss.ntt.co.jp |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
> What I'm requesting here is that the sleep in count_nondeletable_pages()
> be removed and that change backpatched to 8.2 and 8.1.
Agreed. We'd better to shorten the exclusive locking as far as possible.
> We don't know how many pages we can truncate until after we have
> acquired the exclusive lock and examined the pages in question, scanning
> backwards from the end of the table.
But many OSes do not care about read-ahead in backward scanning. I have
a test result that shows truncating a large part of table takes very long
time. Is it better better to change it to forward scanning? For example,
starting with (tail of the file - 16MB) and scanning 16MB of segment forward
to decide the position for truncation. If we can truncate all of the segment,
do recheck from (tail of the file - 32MB) and repeat.
Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center
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