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Re: Review: Fix snapshot taking inconsistencies

From: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Steve Singer <ssinger_pg(at)sympatico(dot)ca>, pgsql-hackers(at)postgresql(dot)org, Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Subject: Re: Review: Fix snapshot taking inconsistencies
Date: 2011-02-28 18:59:05
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On 2011-02-28 8:22 PM, Tom Lane wrote:
> Marko Tiikkaja<marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>  writes:
>> [ latest version of snapshot-taking patch ]
> I started to look at this, and find myself fairly confused as to what
> the purpose is anymore.  Reviewing the thread, there has been a lot of
> discussion of refactoring the API of pg_parse_and_rewrite and related
> functions exported by postgres.c; but the current patch seems to have
> abandoned that goal (except for removing pg_parse_and_rewrite itself,
> which doesn't seem to me to have a lot of point except as part of a
> more general refactoring).  With respect to the issue of changing
> snapshot timing, most of the discussion around that seemed to start
> from assumptions about the behavior of wCTEs that we've now abandoned.
> And there was some discussion about rule behavior too, but it's not
> clear to me whether this patch intends to change that or not.  The
> lack of any documentation change doesn't help here.
> So: exactly what is the intended behavioral change as of now, and what
> is the argument supporting that change?

The only intended change is what I was wondering in the original post: 
snapshot handling between normal execution and EXPLAIN ANALYZE when a 
query expands to multiple trees because of rewrite rules.  Like I said 
earlier, this is just a bugfix now that wCTEs don't need it anymore.

Marko Tiikkaja

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