From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
Cc: | pgsql-patches(at)postgresql(dot)org |
Subject: | Re: Dead Space Map version 3 (simplified) |
Date: | 2007-04-02 20:35:47 |
Message-ID: | 200704022035.l32KZlm09928@momjian.us |
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Thread: | |
Lists: | pgsql-hackers pgsql-patches |
Your patch has been added to the PostgreSQL unapplied patches list at:
http://momjian.postgresql.org/cgi-bin/pgpatches
It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.
---------------------------------------------------------------------------
ITAGAKI Takahiro wrote:
> Attached is an updated DSM patch. I've left the core function of DSM only
> and dropped other complicated features in this release.
>
> VACUUM finishs faster with the patch, but it's obvious... DSM vacuum
> sweeps only pages that have many dead tuples and leave some of them
> after vacuum.
>
> I'll examine the sweep behavior and the performance from now.
>
>
> * Features
> - DSM tracks pages worth vacuuming using 1bit/page bit.
> The threshold is two dead tuples or 2kB of deadspaces.
> - DSM is constructed at page flush. Almost of the works are done by
> bgwriter if it is properly configured.
> - 'VACUUM' command uses DSM. 'VACUUM ALL' always scans all pages.
> - This is including n_dead_tuples statistics fix.
> http://momjian.us/mhonarc/patches/msg00002.html
>
> * Configuration
> - max_dsm_relations (=1000)
> Counterpart to max_fsm_relations, but count tables only;
> Indexes are not tracked by DSM.
> - max_dsm_pages (=1024000)
> Counterpart to max_dsm_pages. Default values are configurated to
> 5 times of max_fsm_pages at initdb.
> - min_dsm_target (=8MB)
> Minimum size of tables of which dead space is tracked
> to avoid tracking small tables, including system catalogs.
>
> * Limitation
> - XID-wraparound vacuum is still required. VACUUM with DSM cannot
> update relfrozenxid, so we sometimes needs full-scan.
> - No recovery support. All contents of DSM and FSM are lost on crash.
> - DSM uses fixed size memory allocated at server start. We cannot change
> the value on-the-fly. If we want the feature, we need something like
> shared-memory-allocator or swap-supported memory management module.
>
> Regards,
> ---
> ITAGAKI Takahiro
> NTT Open Source Software Center
[ Attachment, skipping... ]
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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