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* perfomance question
@ 2004-03-18 06:41 sad <sad@bankir.ru>
2004-03-18 18:38 ` Re: perfomance question Josh Berkus <josh@agliodbs.com>
0 siblings, 1 reply; 4+ messages in thread
From: sad @ 2004-03-18 06:41 UTC (permalink / raw)
To: pgsql-sql
hello.
what are perfomance difference bitween
a) update t1 set f1 = 'x', f2 = 'y';
b) update t1 set f1 = 'x', f2 = f2;
c) update t1 set f1 = 'x';
?
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: perfomance question
2004-03-18 06:41 perfomance question sad <sad@bankir.ru>
@ 2004-03-18 18:38 ` Josh Berkus <josh@agliodbs.com>
2004-03-19 06:27 ` Re: perfomance question sad <sad@bankir.ru>
0 siblings, 1 reply; 4+ messages in thread
From: Josh Berkus @ 2004-03-18 18:38 UTC (permalink / raw)
To: sad <sad@bankir.ru>; pgsql-sql
Sad,
> what are perfomance difference bitween
> a) update t1 set f1 = 'x', f2 = 'y';
> b) update t1 set f1 = 'x', f2 = f2;
> c) update t1 set f1 = 'x';
> ?
Not a lot. Why don't you try it?
--
-Josh Berkus
Aglio Database Solutions
San Francisco
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: perfomance question
2004-03-18 06:41 perfomance question sad <sad@bankir.ru>
2004-03-18 18:38 ` Re: perfomance question Josh Berkus <josh@agliodbs.com>
@ 2004-03-19 06:27 ` sad <sad@bankir.ru>
2004-03-19 07:14 ` Re: perfomance question Adam Ruth <aruth@intercation.com>
0 siblings, 1 reply; 4+ messages in thread
From: sad @ 2004-03-19 06:27 UTC (permalink / raw)
To: pgsql-sql
On Thursday 18 March 2004 21:38, you wrote:
> Sad,
>
> > what are perfomance difference bitween
> > a) update t1 set f1 = 'x', f2 = 'y';
> > b) update t1 set f1 = 'x', f2 = f2;
> > c) update t1 set f1 = 'x';
> > ?
>
> Not a lot. Why don't you try it?
Really ! why ? :-)
I forgot to ask the second question:
How these updates affect a data storage ?
(does (b) cause physical update of f2 ?)
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: perfomance question
2004-03-18 06:41 perfomance question sad <sad@bankir.ru>
2004-03-18 18:38 ` Re: perfomance question Josh Berkus <josh@agliodbs.com>
2004-03-19 06:27 ` Re: perfomance question sad <sad@bankir.ru>
@ 2004-03-19 07:14 ` Adam Ruth <aruth@intercation.com>
0 siblings, 0 replies; 4+ messages in thread
From: Adam Ruth @ 2004-03-19 07:14 UTC (permalink / raw)
To: sad <sad@bankir.ru>; +Cc: pgsql-sql
On Mar 18, 2004, at 11:27 PM, sad wrote:
> On Thursday 18 March 2004 21:38, you wrote:
>> Sad,
>>
>>> what are perfomance difference bitween
>>> a) update t1 set f1 = 'x', f2 = 'y';
>>> b) update t1 set f1 = 'x', f2 = f2;
>>> c) update t1 set f1 = 'x';
>>> ?
>>
>> Not a lot. Why don't you try it?
>
> Really ! why ? :-)
>
> I forgot to ask the second question:
> How these updates affect a data storage ?
> (does (b) cause physical update of f2 ?)
Updates always apply to full rows at a time. So while "update t1 set
f1 = 'x'" only changes the value of f1 to 'x', f2 will have a second
copy with the same value in the new row that is created as part of the
update. It's all part of the MVCC architecture. There may be some
uncommon exceptions to this rule, but I'm not sure.
Adam Ruth
>
>
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings
>
^ permalink raw reply [nested|flat] 4+ messages in thread
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2004-03-18 06:41 perfomance question sad <sad@bankir.ru>
2004-03-18 18:38 ` Josh Berkus <josh@agliodbs.com>
2004-03-19 06:27 ` sad <sad@bankir.ru>
2004-03-19 07:14 ` Adam Ruth <aruth@intercation.com>
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