Re: FDW API: don't like the EXPLAIN mechanism

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>, Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp>, Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: FDW API: don't like the EXPLAIN mechanism
Date: 2011-02-21 16:50:03
Message-ID: 15475.1298307003@sss.pgh.pa.us
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Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Excerpts from Andrew Dunstan's message of lun feb 21 13:11:25 -0300 2011:
>> If we allow the invention of new explain states we'll never be able to
>> publish an authoritative schema definition of the data. That's not
>> necessarily an argument against doing it, just something to be aware of.
>> Maybe we don't care about having EXPLAIN XML output validated.

> The alternative seems to be to let this information proliferate in free
> form (say as text inside some other node), which may be even less convenient.

Yeah; that's exactly what the patch-as-submitted did, and that way was
surely not better from the standpoint of machine parsing the output.
If you really want to lock down the output format to only what is
specified by the core code, then the answer is to forget about giving
FDWs an explain hook at all.

regards, tom lane

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