| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Josh Berkus <josh(at)agliodbs(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Russell Smith <mr-russ(at)pws(dot)com(dot)au>, Jan Wieck <JanWieck(at)yahoo(dot)com> |
| Subject: | Re: Idea for getting rid of VACUUM FREEZE on cold pages |
| Date: | 2010-06-08 12:27:11 |
| Message-ID: | AANLkTint9RWHsO9xOQljtGL4cJ969IFy8Uu-m_JoaXaL@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jun 8, 2010 at 2:26 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> Just an off-the-wall thought, but, would it be possible to have a tool
> which read WAL backwards and compared entries in the WAL against entries
> on disk? I realize that you'd only see one version of a particular
> block and then have to skip any updates which are earlier than it, but
> it seems like you could cover a pretty large chunk of the recent changes
> to the database using this approach..
I assume you mean back out the changes incrementally until you find a
full_page_write and see if it matches? And continue comparing with
full_page_writes once per checkpoint? I don't think the WAL has enough
information to replay backwards though. For example vacuum cleanup
records just list the tids to remove. They don't have the contents to
replace there.
--
greg
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