Re: Buffer usage in EXPLAIN and pg_stat_statements (review)

From: Itagaki Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Euler Taveira de Oliveira <euler(at)timbira(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Buffer usage in EXPLAIN and pg_stat_statements (review)
Date: 2009-10-14 08:44:22
Message-ID: 20091014171946.B1F3.52131E4D@oss.ntt.co.jp
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> 2. I do not understand the stuff with propagating counts into the top
> instrumentation node. That seems like it's going to double-count those
> counts. In any case it is 100% inconsistent to propagate only buffer
> counts that way and not any other resource usage. I think you should
> drop the TopInstrument variable and the logic that propagates counts up.

It is required by contrib/pg_stat_statements. EXPLAIN wants per-node
accumulation, but pg_stat_statements wants the total number.

Is it enough to add a PG_TRY block to standard_ExecutorRun() to
cleanup TopInstrument on error? I'm working on your other comments,
but I cannot remove TopInstrument for pg_state_statements.

I considerd other approaches, but all of them require node-dependent
routines; for example, adding a function to walk through a plan tree
and accumulate instrumentations in it at pg_stat_statements. But it is
hard to be maintained on executor nodes changes. Are there any better idea?

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center

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