| From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
|---|---|
| To: | Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, The Hermit Hacker <scrappy(at)hub(dot)org>, PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Subject: | RE: [HACKERS] Happy column dropping |
| Date: | 2000-01-24 23:48:06 |
| Message-ID: | Pine.LNX.4.21.0001242145450.525-100000@localhost.localdomain |
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| Lists: | pgsql-hackers |
On 2000-01-23, Hiroshi Inoue mentioned:
> Anyway I have 2 basic questions.
>
> 1) Is the * 2x disk usage * implementation really needed ?
Yes, unless you bypass all transaction logic and do a get a row, change
the row, delete the old row, write the new row, and silently hope that no
problems come up down the line. If you do an SQL update of all the rows in
a 10GB table you temporarily need 20GB in case there is a rollback.
> 2) Why rename() ?
> I don't trust rename() at all in transaction control.
> The first thing we should do it to change relname -> relation file
> name mapping in order to avoid calling rename().
That's a good point. The alter table / rename code makes free use of this,
which is just waiting to kick somebody in the head. If you think this
could be addressed in the next release, I'm even for dropping my
business and wait for a cleaner solution.
--
Peter Eisentraut Sernanders väg 10:115
peter_e(at)gmx(dot)net 75262 Uppsala
http://yi.org/peter-e/ Sweden
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