| From: | "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> |
|---|---|
| To: | "'Hannu Krosing'" <hannu(at)tm(dot)ee> |
| Cc: | "'Don Baccus'" <dhogaza(at)pacifier(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, "'Zeugswetter Andreas SB'" <ZeugswetterA(at)wien(dot)spardat(dot)at>, The Hermit Hacker <scrappy(at)hub(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | RE: Plans for solving the VACUUM problem |
| Date: | 2001-05-25 00:23:19 |
| Message-ID: | 3705826352029646A3E91C53F7189E32016655@sectorbase2.sectorbase.com |
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| Lists: | pgsql-hackers |
> > > >Oracle has MVCC?
> > >
> > > With restrictions, yes.
> >
> > What restrictions? Rollback segments size?
> > Non-overwriting smgr can eat all disk space...
>
> Is'nt the same true for an overwriting smgr ? ;)
Removing dead records from rollback segments should
be faster than from datafiles.
> > > You didn't know that? Vadim did ...
> >
> > Didn't I mention a few times that I was
> > inspired by Oracle? -:)
>
> How does it do MVCC with an overwriting storage manager ?
1. System Change Number (SCN) is used: system increments it
on each transaction commit.
2. When scan meets data block with SCN > SCN as it was when
query/transaction started, old block image is restored
using rollback segments.
> Could it possibly be a Postgres-inspired bolted-on hack
> needed for better concurrency ?
-:)) Oracle has MVCC for years, probably from the beginning
and for sure before Postgres.
> BTW, are you aware how Interbase does its MVCC - is it more
> like Oracle's way or like PostgreSQL's ?
Like ours.
Vadim
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