Обсуждение: Odd performance results

I have a table with a 3 column key.  I noticed that when I update a non-key field
in a record of the table that the update was taking longer than I thought it
should.  After much experimenting I discovered that if I changed the data
types of two of the key columns to FLOAT8 that I got vastly improved
performance.

Orignally the data types of the 3 columns were FLOAT4, FLOAT4 and INT4.
My plaform is a PowerPC running Linux.  I speculated that the performance
improvement might be because the PowePC is a 64 bit processor but when
I changed the column data types to INT8, INT8 and INT4 I din't see any
improvement.  I also ran my test code on a Pentium 4 machine with the same
results in all cases.

This doesn't make any sense to me.  Why would FLOAT8 keys ever result
in improved performance?

I verified with EXPLAIN that the index is used in every case for the update.

My postmaster version is 7.1.3.

Any help will be greatly appreciated.

***********************************************************************
Medora Schauer
Sr. Software Engineer

Fairfield Industries
14100 Southwest Freeway
Suite 600
Sugar Land, Tx  77478-3469
USA

mschauer@fairfield.com
***********************************************************************

"Medora Schauer" <mschauer@fairfield.com> writes:
> I have a table with a 3 column key.  I noticed that when I update a non-key field
> in a record of the table that the update was taking longer than I thought it
> should.  After much experimenting I discovered that if I changed the data
> types of two of the key columns to FLOAT8 that I got vastly improved
> performance.

Are there any foreign key linkages to or from this table?  Maybe the
other end of the foreign key is float8?

            regards, tom lane

Orignally there were but in the process of trying to figure
out what is going on I stripped everything out of the database
except the table being queried.

>
> "Medora Schauer" <mschauer@fairfield.com> writes:
> > I have a table with a 3 column key.  I noticed that when I
> update a non-key field
> > in a record of the table that the update was taking longer
> than I thought it
> > should.  After much experimenting I discovered that if I
> changed the data
> > types of two of the key columns to FLOAT8 that I got vastly improved
> > performance.
>
> Are there any foreign key linkages to or from this table?  Maybe the
> other end of the foreign key is float8?
>
>             regards, tom lane
>