Re: [HACKERS] Optimizing GetConflictingVirtualXIDs()

2010-02-14 Thread Tom Lane 
Simon Riggs  writes:
> On Sun, 2010-02-14 at 17:06 +, Greg Stark wrote:
>> EINSUFFICIENTEXPLANATION :)

> ...I like that error code.

I think more EINSUFFICIENTCOMMENTS.  The patch should also add a comment
to the function, along the lines of "While we have the lock, also update
RecentGlobalXmin, so that we will have as up-to-date a value as possible
for next time".  You've also failed to document the meaning or purpose
of the added output parameter.

regards, tom lane

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Re: [HACKERS] Optimizing GetConflictingVirtualXIDs()

2010-02-14 Thread Simon Riggs 
On Sun, 2010-02-14 at 17:06 +, Greg Stark wrote:
> On Sun, Feb 14, 2010 at 2:59 PM, Simon Riggs  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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Re: [HACKERS] Optimizing GetConflictingVirtualXIDs()

2010-02-14 Thread Greg Stark 
On Sun, Feb 14, 2010 at 2:59 PM, Simon Riggs  wrote:
> Optimize GetConflictingVirtualXIDs() in roughly the same manner we
> optimize TransactionIdIsInProgress().
>
> Views?

EINSUFFICIENTEXPLANATION :)


-- 
greg

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