Re: Utilizing multiple disks

Steve wrote:

> Gaetano,
>
> Thanks for your reply.
>
> Gaetano Mendola wrote:
>
>> Are you performing queries using the like operator? If yes did you define
>> an index on it using the right operator class ?
>
>
> Yes I do use the like operator to perform queries on a few 'varchar' and
> 'text' fields. I have indexed almost every column in the table (because
> the client application allows complex searches on multiple columns and
> each column has an equal chance of being used in the 'WHERE' condition)

And did you use the right operator class ?
See http://www.postgresql.org/docs/7.4/interactive/indexes-opclass.html
for details

>> Are you performing queries on a calculated field ? If yes then you need
>> to construct a sort of materialized view.
>
>
> Hmm not sure what you mean by a calculated field. Since I'm not sure
> what it means, I'm probably not using it. I'm definitely not running any
> functions on columns to get an accumulated result back etc.

if you have for example a view like:

CREATE VIEW v_test AS
SELECT foo(a) AS field_1,
bar(a+b) AS field_2
FROM test;

and you do: SELECT * from v_test WHERE field_2 = 123;

then you are in trouble!

>> If you are on Linux did you mounted your data partition with the option
>> noatime ?
>
>
> Yes I'm on linux and am using the ext3 filesystem. I am just about to
> mount the data partition with the noatime option. Docos do say that the
> speed increases considerably. I'll give it a shot but I'm still very
> interested in utilizing the extra three SCSI disks I have at my disposal.

mount that disk in RAID configuration then, you can at least try to move the
WAL on a separate disk.

> Database integrity is of utmost importance and so is speed. I know there
> are tradeoffs but I really do think that moving the data to a separate
> disk will help. Can you please tell me how to set this up? Thanks a lot!
>
> Steve

The version 7.5 will give you the tablespaces feature, in the mean time you
can move your table and or index across your disk using symlinks, moving the
file associated with your table or index in another disk and replace it with a
link.

Regards
Gaetano Mendola