| From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "David E(dot) Wheeler" <david(at)kineticode(dot)com>, "pgsql-hackers(at)postgresql(dot)org Hackers" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Review: listagg aggregate |
| Date: | 2010-01-28 17:19:59 |
| Message-ID: | 162867791001280919u306afd90rfc3a61989eb023e7@mail.gmail.com |
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| Lists: | pgsql-hackers |
2010/1/28 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> in 99.99% the second argument will be a constant. Can we use this
>> information and optimize function for this case?
>
>> The detoast on every row can take some percent from a performance.
>
> What detoast? There won't be one for a constant, nor even for a
> variable in any sane situation --- who's going to be using
> multi-kilobyte delimiter values? And if they do, aren't they likely
> to run out of memory for the result long before the repeated detoasts
> become an interesting problem? You're arguing about a case that
> seems quite irrelevant to the real world.
>
I asking
with get_fn_expr_arg_stable() we are able to fix second parameter
without some performance issues.
Regards
Pavel
> regards, tom lane
>
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