Temp tables being written to disk. Avoidable?

Hi,

I have an application where I am using fulltextindex to
create a searchable index for a table and wish to return
pages of results, ranked in order of relevance. So for any
particular page view I need to know:
a) Total number of results relevant to search (so I can display   page [1] 2 3 4 5 6)
b) The results to be ranked by 'relevance' to search terms.
c) The details for a part of that range (ie 15 or so entries   per page.

Database structure is something like:

======
txdev400003=# \d entry_fti             Table "entry_fti"Attribute |         Type          | Modifier 
-----------+-----------------------+----------string    | character varying(25) | id        | oid                   | 
Index: entry_fti_idx

txdev400003=# \d entry                             Table "entry"   Attribute     |   Type   |               Modifier
               
 
------------------+----------+------------------------------------entry_id         | integer  | default
nextval('ent_id_seq'::text)name            | text     | description_html | text     | fti_text         | text     | 
 
Indices: entry_oid_idx,        entry_pkey
======
(The entry table is simplified here, real one has 24 columns).

My original plan was to do two/three queries, ie:
======
SELECT COUNT (entry_fti.id) as rating , id 
INTO TEMP TABLE searchtemp 
FROM entry_fti  
WHERE (entry_fti.string ~'^word1' OR entry_fti.string ~'^word2') 
GROUP BY id

SELECT entry.*, searchtemp.rating 
FROM searchtemp, entry 
WHERE entry.oid=searchtemp.id 
ORDER BY rating DESC 
LIMIT 15 OFFSET 0

SELECT count(*) FROM searchtemp; 
(optional, depending on number of rows returned by previous query)
======

This seemed to be the cheapest way to get all the information I need.
However, I noticed a disk access each time I did the search. I fiddled
with the SHARED_BUFFERS and SORT_MEM and discovered they weren't the
problem but that the SELECT INTO was causing the disk access. If I have
multiple searches occuring concurrently I imagine this becoming a 
problem. Can I avoid having the temp table written to disk (unless
required by running out of memory)? The temp table has a tiny lifespan
and needs to be accessed for each subsequent query so there's no
point in writing it to disk unless completely necessary.

For the moment I have moved to a query like:
======
SELECT COUNT (entry_fti.id) as rating , entry_id, name, description_html
FROM entry_fti, entry 
WHERE (entry_fti.string ~'^word1' OR entry_fti.string ~'^word2') 
AND entry_fti.id=entry.oid 
GROUP BY id ,entry_id, name, description_html
ORDER BY rating DESC
======
which seems significantly less elegant (I need to return all rows and
do my 'OFFSET' and 'LIMIT' manually, also bearing in mind that I'm
pulling 20+ cols from the entry table, not the 3 I have here) but 
doesn't cause any disk access as the entry_fti and entry tables sit
in memory.

Hmm, I should to do some proper benchmarking on this rather than
worrying about the noises coming from the disks..

However, even if the original method does turn out to be faster,
I imagine it could be faster still without the disk writes (though
I don't know anywhere near enough about the PostgreSQL internals
for that to be anything other than a gut feeling).

--
Paul McGarry            mailto:paulm@opentec.com.au 
Systems Integrator      http://www.opentec.com.au 
Opentec Pty Ltd         http://www.iebusiness.com.au
6 Lyon Park Road        Phone: (02) 9870 4718 
North Ryde NSW 2113     Fax:   (02) 9878 1755 
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