> I am using a simple PostgreSQL 7.3 database in a soft-realtime
> application.

Then you're not going to like the answer I have for you, see below.

> I have a problem where an update on a record within a (fully indexed)
> table containing less than ten records needs to occur as fast as
> possible.

Have you considered dropping the indexes?  On such a small table, they won't 
be used, and they are detracting significantly from your update speed.

> Immediately after performing a vaccum, updates take upto 50 milliseconds
> to occur, however the update performance degrades over time, such that
> after a few hours of continuous updates, each update takes about half a
> second. Regular vacuuming improves the performance temporarily, but
> during the vacuum operation (which takes upto 2 minutes), performance of
> concurrent updates falls below an acceptable level (sometimes > 2
> seconds per update).

This is "normal" depending on your platform and concurrent activity.   More 
frequent vacuums would take less time each.   What is your max_fsm_pages set 
to?   Increasing this may decrease the necessity of vacuums as well as 
speeding them up.  Also, are you vacuuming the whole DB or just that table?  
2 mintues seems like a long time; I can vacuum a 100GB database in less than 

> Is there a way to disable this behaviour such that an update operation
> would overwrite the current record and does not generate an outdated
> tuple each time? (My application does not need transactional support).

No.  Our ACID Transaction compliance depends on "that behaviour" (MVCC).  We 
don't offer PostgreSQL in a "non-ACID mode".   If your application truly does 
not need transactional support, you may want to consider an embedded database 
instead, such as BerkeleyDB or SQLite.    PostgreSQL has a *lot* of "baggage" 
associated with having 99.99% incorruptable transactions.

Alternately, you may also want to take a look at TelegraphCG, a derivative of 
PostgreSQL designed to handle "streaming data".  They may have already 
conquered some of your difficulties for you.

Were I you, I would start with tuning the database first through 
PostgreSQL.conf and a careful look at my hardware usage and DB maintenance.   
Then I would consider testing 8.0, which has some specific improvements 
designed to address some of the problems you are having.   Particularly, 
Jan's Background Writer and Lazy Vacuum.

Josh Berkus
Aglio Database Solutions
San Francisco

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