| From: | "Zeugswetter Andreas DAZ SD" <ZeugswetterA(at)spardat(dot)at> |
|---|---|
| To: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Bruno Wolff III" <bruno(at)wolff(dot)to>, "Greg Stark" <gsstark(at)mit(dot)edu>, "Russell Smith" <mr-russ(at)pws(dot)com(dot)au>, <josh(at)agliodbs(dot)com>, "Postgres Hackers" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Checkpoint cost, looks like it is WAL/CRC |
| Date: | 2005-07-07 10:11:43 |
| Message-ID: | E1539E0ED7043848906A8FF995BDA57945BA2D@m0143.s-mxs.net |
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| Lists: | pgsql-hackers |
> Here's an idea:
>
> We read the page that we would have backed up, calc the CRC and
> write a short WAL record with just the CRC, not the block. When
> we recover we re-read the database page, calc its CRC and
> compare it with the CRC from the transaction log. If they
> differ, we know that the page was torn and we know the database
> needs recovery. (So we calc the CRC when we log AND when we recover).
Won't work, since the page on disk may have x different contents
between 2 checkpoints (bgwriter from lru).
Only workable solution would imho be to write the LSN to each 512
byte block (not that I am propagating that idea).
Andreas
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