Garbage Collecting

Joshua Berry wrote:

I'm a postgresql newbie that's inherited eight production servers
running Postgresql 8.2.5 as the backend. I have many questions
covering topics such as administration of the database (upgrading,
maintaining conf files, etc), improving the schema of the system (many
tables don't currently have primary keys; to do anything useful you
must join at least 5 tables), optimizing poor performing queries that
can take hours, and knowing where functionality of the system should
reside (curenly as PL/SQL functions, as external c code, external php
code, and external perl code).

Indexing can be a win once you figure out which quires are run the most
and what the common where clauses look like. Indexes can eat up allot
of disk space and slow performance in other places. Its a double edge
sword.

http://www.postgresql.org/docs/8.2/interactive/sql-createindex.html

The database I maintain has far more Reads by a factor of 10,000 times
to inserts, updates, and deletes combine so having many indexes is a
win in my case. This is the part of tuning the database to the load.

http://wiki.postgresql.org/wiki/Performance_Optimization
http://wiki.postgresql.org/wiki/Database_Administration_and_Maintenance

Please refer me to appropriate documentation/FAQs/books. I've read
http://www.postgresql.org/docs/faqs.FAQ.html If anyone knows of
writeups for newbies that touches upon the things I mentioned, that
would probably be really helpful for me.

http://wiki.postgresql.org/wiki/Main_Page
and the help files with comments has lots of helpful information. Just
make sure that you are reading information related to the version of
Postgresql you are running.

http://www.postgresql.org/docs/8.2/interactive/index.html

I have one specific question about "Garbage Collecting" within the
database. The database system I'm working with has data that is no
longer needed after a period of time. For example: transaction records
only need to be kept around for the last 31 days; php web sessions
that don't need to persist longer than a day. Could I create some
function in the database that would act a bit like a daily cron job
that deletes old records from tables (and then performs the
appropriate VACUUM to regain the space)?

Yes you can do this with pgAgent it comes with pgAdmin
http://www.pgadmin.org/docs/1.4/pgagent.html
http://www.pgadmin.org/

If the records have a date when added then a command like so can be
scheduled

Delete from Mytable where DateAdded <= (Current_date - '31 day
'::interval' )::date

If yes, how does one impliment something like that? As a trigger
function written in PL/SQL? Can I hook the function into something
that executes once per day?

Yes it can be written in PL/SQL function then have pgAgent call it at
midnight or at sometime thats off peak load times.

Also you want to make sure autovaccum is turned to your needs

http://www.postgresql.org/docs/8.2/static/routine-vacuuming.html
this can have big impacts on performance.

If no, why? Should the external scripts/code that puts the data into
the database be responsible for removing the old data?

It really does not matter.