| From: | "tsunakawa(dot)takay(at)fujitsu(dot)com" <tsunakawa(dot)takay(at)fujitsu(dot)com> |
|---|---|
| To: | 'Peter Smith' <smithpb2250(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, "osumi(dot)takamichi(at)fujitsu(dot)com" <osumi(dot)takamichi(at)fujitsu(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | RE: Implement UNLOGGED clause for COPY FROM |
| Date: | 2020-09-11 05:15:32 |
| Message-ID: | TYAPR01MB2990ED6B394A9B4B51D28569FE240@TYAPR01MB2990.jpnprd01.prod.outlook.com |
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| Lists: | pgsql-hackers |
From: Peter Smith <smithpb2250(at)gmail(dot)com>
On Thu, Sep 10, 2020 at 7:16 PM tsunakawa(dot)takay(at)fujitsu(dot)com
> <tsunakawa(dot)takay(at)fujitsu(dot)com> wrote:
> > ALTER TABLE takes long time proportional to the amount of existing data,
> while wal_level = none doesn't.
>
> Right, but if wal_level=none is considered OK for that table with
> existing data, then why not just create the table UNLOGGED in the
> first place? (or ALTER it to set UNLOGGED just one time and then leave
> it as UNLOGGED).
The target tables sometimes receive updates (for data maintenance and/or correction). They don't want those updates to be lost due to the database server crash. Unlogged tables lose their entire contents during crash recovery.
Please think like this: logging is is the norm, and unlogged operations are exceptions/hacks for some requirement of which the user wants to minimize the use.
Regards
Takayuki Tsunakawa
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