| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, postgres performance list <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Blocking excessively in FOR UPDATE |
| Date: | 2011-11-04 16:10:37 |
| Message-ID: | CA+TgmoZ3n5a5kKvO6cFwUEa5eBQWK=s8nvy_-86eP82nFv8Eig@mail.gmail.com |
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| Lists: | pgsql-performance |
On Fri, Nov 4, 2011 at 12:07 PM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> What are those writes about? HOT vacuuming perhaps?
Every tuple lock requires dirtying the page. Those writes are all
those dirty pages getting flushed out to disk. It's possible that the
OS is allowing the writes to happen asynchronously for a while, but
then when you get too much dirty data in the cache, it starts
blocking.
The only thing I'm fuzzy about is why it's locking so many rows, given
that the output says rows=1.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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