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Re: Reduce the size of PageFreeSpaceInfo on 64bit platform

From: ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
To: Decibel! <decibel(at)decibel(dot)org>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Reduce the size of PageFreeSpaceInfo on 64bit platform
Date: 2007-08-13 01:40:31
Message-ID: 20070813102754.6A35.ITAGAKI.TAKAHIRO@oss.ntt.co.jp (view raw or flat)
Thread:
Lists: pgsql-patches
Decibel! <decibel(at)decibel(dot)org> wrote:

> > The sizeof(PageFreeSpaceInfo) is 16 bytes
 
> So... does that mean that the comment in the config file about 6 bytes
> per page is incorrect?

There are no comments the usage of maintenance_work_mem in the config file
nor the documentation. Memory consumed by max_fsm_pages is only mentioned.

#maintenance_work_mem = 16MB # min 1MB
#max_fsm_pages = 204800      # min max_fsm_relations*16, 6 bytes each


But surely the difference of memory usage between maintenance_work_mem
and max_fsm_pages might confuse users. I'll rewrite my patch to use
FSMPageData in both places so that users can always estimate the memory
to 6 bytes per page.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center



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