On Thursday 20 November 2003 20:29, Shridhar Daithankar wrote:
> On Thursday 20 November 2003 20:00, Matthew T. O'Connor wrote:
> > Shridhar Daithankar wrote:
> > > I will submit a patch that would account deletes in analyze threshold.
> > > Since you want to delay the analyze, I would calculate analyze count as
> >
> > deletes are already accounted for in the analyze threshold.
>
> Yes. My bad. Deletes are not accounted in initializing analyze count but
> later they are used.
>
> > > I am still wary of inverting vacuum analyze frequency. You think it is
> > > better to set inverted default rather than documenting it?
> >
> > I think inverting the vacuum and analyze frequency is wrong.
>
> Me. Too. ATM all I can think of this patch attached. Josh, is it sufficient
> for you?..:-)
use this one. A warning added for too aggressive vacuumming. If it is OK by
everybody, we can send it to patches list.
Shridhar
*** README.pg_autovacuum.orig Thu Nov 20 19:58:29 2003
--- README.pg_autovacuum Thu Nov 20 20:35:34 2003
***************
*** 141,163 ****
depending on the mixture of table activity (insert, update, or
delete):
! - If the number of (inserts + updates + deletes) > AnalyzeThreshold, then
only an analyze is performed.
! - If the number of (deletes + updates) > VacuumThreshold, then a
vacuum analyze is performed.
VacuumThreshold is equal to:
! vacuum_base_value + (vacuum_scaling_factor * "number of tuples in the table")
!
AnalyzeThreshold is equal to:
! analyze_base_value + (analyze_scaling_factor * "number of tuples in the table")
!
The AnalyzeThreshold defaults to half of the VacuumThreshold since it
represents a much less expensive operation (approx 5%-10% of vacuum),
and running ANALYZE more often should not substantially degrade system
performance.
Sleeping:
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--- 141,191 ----
depending on the mixture of table activity (insert, update, or
delete):
! - If the number of (inserts + updates + deletes) >= AnalyzeThreshold, then
only an analyze is performed.
! - If the number of (deletes + updates) >= VacuumThreshold, then a
vacuum analyze is performed.
VacuumThreshold is equal to:
! vacuum_base_value + (vacuum_scaling_factor * "number of tuples in the
! table")
AnalyzeThreshold is equal to:
! analyze_base_value + (analyze_scaling_factor * "number of tuples in the
! table")
The AnalyzeThreshold defaults to half of the VacuumThreshold since it
represents a much less expensive operation (approx 5%-10% of vacuum),
and running ANALYZE more often should not substantially degrade system
performance.
+ Examples:
+
+ Following table shows typical usage of pg_autovacuum settings.
+ These are put here so that a DBA can have some starting point while
+ tuning pg_autovacuum.
+
+ Vacuum is triggered by updates and deletes. So in case of vacuum,
+ last column indicates total of updates and deletes required
+ to trigger vacuum. In case of analyze, the operations would count total
+ number of inserts, updates and deletes.
+
+ Base Scaling factor Records No. of Operations
+ 1,000 1 10,000 11,000
+ 1,000 2 10,000 21,000
+ 1,000 0.5 10,000 6,000
+ 1,000 0.1 10,000 2,000
+
+ Although analyze is cheaper operation compared to vacuum,
+ it might be needed less often. The default is to analyze twice as much as
+ vacuum but that might be too aggressive for some installations. It is advised
+ thatsuch installation tune their analyze threshold separately, rather than
+ relying upon the default behaviour.
+
+ Furthermore, for aggressive vacuum/analyze behaviour, it is recommended that
+ scaling factor is set to less than 1. However too aggresive operation can affect
+ performance of normal database operations adversely. Do not apply such setting
+ to production databases without prior testing.
+
Sleeping:
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