Re: Load TIME fields - proposed performance improvement

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Smith <smithpb2250(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Load TIME fields - proposed performance improvement
Date: 2020-09-22 02:44:27
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I wrote:
> Interesting idea, but this implementation is leaving a *lot*
> on the table. If we want to cache the result of
> timestamp2tm applied to GetCurrentTransactionStartTimestamp(),
> there are half a dozen different call sites that could make
> use of such a cache, eg, GetSQLCurrentDate and GetSQLCurrentTime.

As an example, I did some quick-and-dirty "perf" measurement of
this case:

create table t1 (id int, d date default current_date);
insert into t1 select generate_series(1,100000000);

and found that about 10% of the runtime is spent inside timestamp2tm().
Essentially all of that cost could be removed by a suitable caching
patch. Admittedly, this is a pretty well cherry-picked example, and
more realistic test scenarios might see just a percent or two win.
Still, for the size of the patch I'm envisioning, it'd be well
worth the trouble.

regards, tom lane

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