Re: Push down time-related SQLValue functions to foreign server

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Cc: Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>, Zhihong Yu <zyu(at)yugabyte(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Push down time-related SQLValue functions to foreign server
Date: 2022-01-18 05:43:58
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Corey Huinker <corey(dot)huinker(at)gmail(dot)com> writes:
> I'm very late to the party, but it seems to me that this effort is
> describing a small subset of what "routine mapping" seems to be for:
> defining function calls that can be pushed down to the foreign server, and
> the analogous function on the foreign side. We may want to consider
> implementing just enough of CREATE ROUTINE MAPPING and DROP ROUTINE MAPPING
> to support these specific fixed functions.

Hmm ... not really, because for these particular functions, the
point is exactly that we *don't* translate them to some function
call on the remote end. We evaluate them locally and push the
resulting constant to the far side, thus avoiding issues like
clock skew.

Having said that: why couldn't that implementation sketch be used
for ANY stable subexpression? What's special about the datetime

regards, tom lane

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