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Re: Optimizing GetConflictingVirtualXIDs()

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Optimizing GetConflictingVirtualXIDs()
Date: 2010-02-14 17:39:28
Message-ID: 1266169168.7341.9433.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sun, 2010-02-14 at 17:06 +0000, Greg Stark wrote:
> On Sun, Feb 14, 2010 at 2:59 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > Optimize GetConflictingVirtualXIDs() in roughly the same manner we
> > optimize TransactionIdIsInProgress().
> >
> > Views?
> 
> EINSUFFICIENTEXPLANATION :)

...I like that error code.


The patch adds a calculation of RecentGlobalXmin each time it accesses
the proc array to derive conflicts. It then uses the derived value to
provide a fast-path out if a potential snapshot conflict arrives that we
already know will not conflict with any backends. The purpose of this is
to reduce the number of scans of the procarray and improve the
performance of the startup process.

The mechanism and purpose is the same as the first check in
TransactionIdIsInProgress().

-- 
 Simon Riggs           www.2ndQuadrant.com


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