| From: | "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> |
|---|---|
| To: | "'Zeugswetter Andreas SB'" <ZeugswetterA(at)wien(dot)spardat(dot)at>, "'Bruce Momjian'" <pgman(at)candle(dot)pha(dot)pa(dot)us>, Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp> |
| Cc: | The Hermit Hacker <scrappy(at)hub(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | RE: Plans for solving the VACUUM problem |
| Date: | 2001-05-24 17:30:39 |
| Message-ID: | 3705826352029646A3E91C53F7189E32016651@sectorbase2.sectorbase.com |
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| Lists: | pgsql-hackers |
> If PostgreSQL wants to stay MVCC, then we should imho forget
> "overwriting smgr" very fast.
>
> Let me try to list the pros and cons that I can think of:
> Pro:
> no index modification if key stays same
> no search for free space for update (if tuple still
> fits into page)
> no pg_log
> Con:
> additional IO to write "before image" to rollback segment
> (every before image, not only first after checkpoint)
> (also before image of every index page that is updated !)
I don't think that Oracle writes entire page as before image - just
tuple data and some control info. As for additional IO - we'll do it
anyway to remove "before image" (deleted tuple data) from data files.
Vadim
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