| From: | "Kevin T(dot) Manley \(Home\)" <kmanley(at)uswest(dot)net> |
|---|---|
| To: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: WAL & SHM principles |
| Date: | 2001-03-07 21:44:12 |
| Message-ID: | 986a4v$2u6l$1@news.tht.net |
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| Lists: | pgsql-hackers |
""Mikheev, Vadim"" <vmikheev(at)SECTORBASE(dot)COM> wrote in message
news:8F4C99C66D04D4118F580090272A7A234D32FA(at)sectorbase1(dot)sectorbase(dot)com(dot)(dot)(dot)
> > It is possible to build a logging system so that you mostly don't care
> > when the data blocks get written; a particular data block on disk is
> > considered garbage until the next checkpoint, so that you
>
> How to know if a particular data page was modified if there is no
> log record for that modification?
> (Ie how to know where is garbage? -:))
>
You could store a log sequence number in the data page header that indicates
the log address of the last log record that was applied to the page. This is
described in Bernstein and Newcomer's book (sec 8.5 operation logging).
Sorry if I'm misunderstanding the question. Back to lurking mode...
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