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Re: Review of Writeable CTE Patch

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>
Cc: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Merlin Moncure <mmoncure(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Review of Writeable CTE Patch
Date: 2010-02-03 16:49:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Wed, Feb 3, 2010 at 11:18 AM, Marko Tiikkaja
<marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> wrote:
>> In ExecTopLevelStmtIsReadOnly, you might perhaps want to rephase the
>> comment in a way that doesn't use the word "Ehm."  Like maybe: "Even
>> if this function returns true, the statement might still contain
>> UPDATE, or DELETE statements within a CTE; we only check the top-level
>> statement."  Also, there should be a newline immediately before the
>> function name, per our usual style conventions.
> That comment tries to emphasize the fact that I can't think of any
> reasonable name for that particular function.  If the name looks OK, I
> can update the comment.

Name seems fine.  Just fix the comment.

>> The limitations of INSERT/UPDATE/DELETE-within-WITH should be
>> documented somewhere: top level CTE only, and no DO ALSO or
>> conditional DO INSTEAD rules.  If we don't intend to remove this
>> limitation in a future release, we should probably also document that.
>>  I believe there are some other caveats that we've discussed before,
>> too, though I'm not sure if they're still true.  Stuff like:
>> - CTEs will be executed to completion in sequential order before the
>> main statement begins execution
>> - each CTE will see the results of CTEs already executed, and the main
>> statement will see the results of all CTEs
>> - but queries within each CTE still won't see their own updates (a
>> reference to whatever section of the manual we talk about this in
>> would probably be good)
>> - possible pitfalls of CTEs not being pipelined
> Right.  The documentation in its current state is definitely lacking.
> I've tried to focus all the time I have in making this patch technically
> good.

Well, technically good is certainly a good place to start.  :-)  Of
course, we need the docs, too.  Thanks for your work on this.


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