Re: ProcessUtility_hook

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: Bruce Momjian <bruce(at)momjian(dot)us>, Euler Taveira de Oliveira <euler(at)timbira(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: ProcessUtility_hook
Date: 2009-12-03 07:05:47
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> ... and now that I have, I find at least four highly questionable
> things about it:
> 1. The placement of the hook. Why is it three lines down in
> ProcessUtility? It's probably reasonable to have the Assert first,
> but I don't see why the hook function should have the ability to
> editorialize on the behavior of everything about ProcessUtility
> *except* the read-only-xact check.

I moved the initialization of completionTag into standard_ProcessUtility.

> 2. The naming and documentation of the added GUC setting for
> pg_stat_statements. "track_ddl" seems pretty bizarre to me because
> there are many utility statements that no one would call DDL. COPY,
> for example, is certainly not DDL. Why not call it "track_utility"?

Ok, fixed.

> 3. The enable-condition test in pgss_ProcessUtility. Is it really
> appropriate to be gating this by isTopLevel? I should think that
> the nested_level check in pgss_enabled would be sufficient and
> more likely to do what's expected.

I removed the isTopLevel check. I was worried about auto-generated
utility commands; generated sub commands are called with the same
query string as the top query. Don't it confuse statistics?

> 4. The special case for CopyStmt. That's just weird, and it adds
> a maintenance requirement we don't need. I don't see a really good
> argument why COPY (alone among utility statements) deserves to have
> a rowcount tracked by pg_stat_statements, but even if you want that
> it'd be better to rely on examining the completionTag after the fact.
> The fact that the tag is "COPY nnnn" is part of the user-visible API
> for COPY and won't change lightly. The division of labor between
> ProcessUtility and copy.c is far more volatile, but this patch has
> injected itself into that.

Ok, fixed. I've thought string-based interface is not desirable, but it
should be a stable API. COPY and INSERT/UPDATE/DELETE (used by EXECUTE)
are counted by pg_stat_statements, but EXECUTE SELECT is impossible.

ITAGAKI Takahiro
NTT Open Source Software Center

Attachment Content-Type Size
ProcessUtility_hook_20091203.patch application/octet-stream 11.2 KB

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