Re: Excessive WAL generation and related performance issue

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On 04/14/2014 05:40 PM, Stephen Frost wrote:
> This sounds like a great example of the unlogged table -> logged
> table use-case and makes me wonder if we could provide an
> optimization similar to the existing CREATE TABLE + COPY under
> wal_level = minimal case, where we wouldn't WAL log anything for
> CREATE TABLE + COPY even when wal_level is above minimal, until
> COMMIT, at which point we'll blast the whole thing out in one
> shot.

I was definitely thinking that it would be nice if we could alter this
table to make it unlogged, load it, and then alter again to make it
logged. Obviously easier said than done though ;-)

> Another option that you might consider is ordering your input, if
> possible, to improve the chances that the same page is changed
> multiple times inside a given checkpoint, hopefully reducing the
> number of pages changed.

Nice idea but doesn't work well when you have two indexes with
different first column correlations.

Joe

- --
Joe Conway
credativ LLC: http://www.credativ.us
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