Temporary tables and disk activity

Dear All,

I sent a message last weekend asking about temporary tables being 
written to disk but didn't get any replies.  I'm sure there is someone 
out there who knows something about this - please help!  Here is the 
question again:


Looking at vmstat output on my database server I have been suprised to 
see lots of disk writes going on while it is doing what should be 
exclusively read-only transactions. I see almost no disk reads as the 
database concerned is small enough to fit into the OS disk cache.

I suspect that it might be something to do with temporary tables. There 
are a couple of places where I create temporary tables to "optimise" 
queries by factoring out what would otherwise be duplicate work. The 
amount of data being written is of the right order of magnitude for this 
to be the cause. I fear that perhaps Postgresql is flushing these tables 
to disk, even though they will be dropped before the end of the 
transaction. Is this a possibility? What issues should I be aware of 
with temporary tables? Are there any other common causes of lots of disk 
writes within read-only transactions? Is there any debug output that I 
can look at to track this down?

Thanks in advance for any help that you can offer.

Regards,

Phil Endecott.