From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "osumi(dot)takamichi(at)fujitsu(dot)com" <osumi(dot)takamichi(at)fujitsu(dot)com> |
Cc: | "'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: | 2020-07-10 14:01:00 |
Message-ID: | 2056330.1594389660@sss.pgh.pa.us |
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"osumi(dot)takamichi(at)fujitsu(dot)com" <osumi(dot)takamichi(at)fujitsu(dot)com> writes:
>> Aside from that, though, how does this improve upon the existing capability to copy into an unlogged temporary table?
> [>] unlogged temporary table can’t be inherited over sessions first of all.
Unlogged tables don't have to be temporary.
> And unlogged table needs to be recreated due to startup truncation of the table’s content
> when the server crashes.
Indeed, and your proposed feature would extend that un-safety to tables
that are NOT marked unlogged, which is not good.
AFAICS, we can already accomplish basically the same thing as what you
want to do like this:
alter table foo set unlogged;
copy foo from ...;
alter table foo set logged;
The mechanics of that are already well worked out. It's expensive,
no doubt about that, but I think you're just fooling yourself to
imagine that any shortcuts are possible. A mix of unlogged and logged
data is never going to work safely.
> To achieve this, we have to
> consider a new idea like loaded data’d be added
> at the end of the all other pages and detach those
> if the server crashes during the UNLOGGED loading processing for example.
You keep on ignoring the indexes... not to mention replication.
regards, tom lane
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