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Re: crash-safe visibility map, take three

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: crash-safe visibility map, take three
Date: 2010-11-30 16:22:03
Message-ID: AANLkTi=7St=B=MONtpwD7eTQe9o2Vzd2j5Vfs0wnmj0b@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Nov 30, 2010 at 11:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> How much is "quite a lot"?  Do we have any real reason to think that
> this solution is unacceptable performance-wise?

Well, let's imagine a 1GB insert-only table.  It has 128K pages.  If
you XLOG setting the bit on each page, you'll need to write 128K WAL
records, each containing a 12-byte relfilenode and a 4-byte block
offset, for a total of 16 bytes of WAL per page, thus 2MB of WAL.

But you did just dirty a gigabyte of data.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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Subject: Re: [GENERAL] column-level update privs + lock table
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Subject: Re: crash-safe visibility map, take three

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