| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Martijn van Oosterhout <kleptog(at)svana(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: WAL logging problem in 9.4.3? |
| Date: | 2015-07-10 10:29:02 |
| Message-ID: | 20150710102902.GL340@alap3.anarazel.de |
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| Thread: | |
| Lists: | pgsql-hackers |
On 2015-07-10 19:23:28 +0900, Fujii Masao wrote:
> Maybe I'm missing something. But I start wondering why TRUNCATE
> and INSERT (or even all the operations on the table created at
> the current transaction) need to be WAL-logged while COPY can be
> optimized. If no WAL records are generated on that table, the problem
> we're talking about seems not to occur. Also this seems safe and
> doesn't degrade the performance of data loading. Thought?
Skipping WAL logging means that you need to scan through the whole
shrared buffers to write out dirty buffers and fsync the segments. A
single insert wal record is a couple orders of magnitudes cheaper than
that. Essentially doing this juts for COPY is a heuristic.
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