Re: 9.2.1 & index-only scans : abnormal heap fetches after VACUUM FULL

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Jaime Casanova <jaime(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)mail(dot)com>, Amit Kapila <amit(dot)kapila(at)huawei(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 9.2.1 & index-only scans : abnormal heap fetches after VACUUM FULL
Date: 2014-02-16 02:34:15
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On Sat, Feb 15, 2014 at 07:08:40PM +0100, Andres Freund wrote:
> > Can you be more specific about the cluster.c idea? I see
> > copy_heap_data() in cluster.c calling HeapTupleSatisfiesVacuum() with a
> > 'buf' just like the code I am working in.
> Yes, it does. But in contrast to your patch it does so on the *origin*
> buffer. Which is in shared memory.
> The idea would be to modify rewrite_heap_tuple() to get a new parameter
> informing it it about the tuple's visibility. That'd allow you to avoid
> doing any additional visibility checks.
> Unfortunately that would still not fix the problem that
> visibilitymap_set requires a real buffer to be passed in. If you're
> going that route, you'll need to make a bit more sweeping changes. You'd
> need to add new blockno parameter and a BufferIsValid() check to the
> right places in log_heap_visible(). Pretty ugly if you ask me...

Thank you for the thorough review. Unless someone else can complete
this, I think it should be marked as returned with feedback. I don't
think I am going to learn enough to complete this during the

Since learning of the limitations in setting vmmap bits for index-only
scans in October, I have been unable to improve VACUUM/CLUSTER, and
unable to improve autovacuum --- a double failure. I guess there is
always PG 9.5.

Bruce Momjian <bruce(at)momjian(dot)us>

+ Everyone has their own god. +

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