| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Subplan result caching |
| Date: | 2018-05-23 16:51:38 |
| Message-ID: | 9165.1527094298@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On 23/05/18 19:25, Tom Lane wrote:
>> To make this
>> patch safe, I think you'd need to grovel through the subquery and make
>> sure that the parameters are only used as inputs to operators that belong
>> to the type's default btree or hash opfamily. (Many other cases would
>> work in practice, but we have no semantic knowledge that would let us be
>> sure of that.)
> Hmm. First thing that comes to mind is to use the raw bytes as cache
> key, only treating Datums as equal if their binary representation is
> identical.
Ah. That would work, though it'd make the number of subquery executions
even less predictable (since some logically-equal values would compare
as physically unequal).
regards, tom lane
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