Continual Postgres headaches...

I've been trying for quite a while to get Postgresql tuned for use as an OLTP system.  I have several PL/pgSQL functions that handle inserts and updates to the main table and several near-real-time daemons written that access the data and can take automated actions on it (email/page concerned people, get complimentary information from a different system, etc.).  I started with Postgres 8.1 and am now using 8.2.4 (and have been since its release).  I'll try to provide enough information for a decent response, but as I can't obviously put my entire schema and database out there, I'm hoping that I can get some decent guidelines beyond that what I've found though Google, etc. to get this thing tuned better.

Most of the data centers in on a central table and has 23 columns, 1 constraint, and 9 indexes.  4 of the indexes are partial.  The table usually contains about 3-4 million rows, but I've cut it down to 1.2 million (cut out 2/3 of the data) in an effort to migrate the database to a 2^nd sever for more testing.  The two partial indexes used the most: 242MB accessed nearly constantly, and 15MB accessed every 5 seconds - but also updated constantly via inserts using the 242MB index.  Other than one other 25MB index, the others seem to average around 300MB each, but these aren't used quite as often (usually about every minute or so).

My problems really are with performance consistency.  I have tweaked the execution so that everything should run with sub-second execution times, but even after everything is running well, I can get at most a week or two of steady running before things start to degrade.

In my efforts to correct these consistency in execution problems, I have gone from vacuuming (with analyze) twice a day to every 30 minutes (how long it takes a vacuum analyze to run - another seeming problem because it shouldn't take so long?).  I've done a VACUUM FULL and that sometimes helps, but obviously is not a long-term solution for a true OLTP system.  Why I said "sometimes helps": earlier this week I did a VACUUM FULL, VACUUM ANALYZE on the entire schema. A query that was supposed to use the 25MB index above (that matched the parameters of the partial index exactly) was still not doing so.  I had to DROP and re-CREATE the index (and do another ANALYZE) to get the database to (correctly) use the index.

Another problem: sometimes I get these unexplainable delays in using a 'stored procedure' even though all its SQL calls run just fine individually.  For example, calling a particular function will take 1 minute to execute even though entering the SQL commands individually through psql will total up to about 1 second.  When I log 'long-duration queries', I only see the top function call in the log.  When I put 'RAISE NOTICE' statements in the various PL/pgSQL functions, I only see them displayed for the function I call directly; any underlying functions called from that function does not show any of their NOTICE statements.  Because of this I can't track down where the delays are occurring for me to try and correct the problem (not that there should be one in the first place)!  I should also note that there is not any lock contention (double-checked with pgadmin3) showing that would "artificially" delay the queries...

I've played with quite a few of the parameters like vacuum_cost_delay, work_mem, shared_buffers, turned fsync off, etc. in the postgresql.conf file.  The server I've been given to use is quite old (read: not the fastest anymore), but normally shows a load average of 0.25.to 0.50 or so.

I guess my questions boil down to what I can do other than use the EXPLAIN, EXPLAIN ANALYZE, VACUUM ANALYZE, etc. to get my schema performing acceptably across the board in a consistent manner.  If there is more information that I can give out that would improve responses, please let me know.

Thanks in advance for any help you send my way!