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
