important decrease of performance using the BETA version in one particular case

(sorry for previous HTML)

Your name: Isabelle Therrien
Your email address : therriei(at)cirano(dot)qc(dot)ca

System Configuration
---------------------
Architecture : Intel Pentium

Operating System : Linux

PostgreSQL version : PostgreSQL-7.1 Beta (but I use JDBC drivers
v7.0.2)

I'm using Weblogic Server 5.1

Please enter a FULL description of your problem:
------------------------------------------------
I observed an important decrease of performance using the BETA version of
PostgreSQL in one
particular case:

I have a big query, reported below, that is called several times in my
application.
At least 4 active connections call it at the same time.
Normally, this query is executed in about 30-50 milliseconds.
But after a while (depending on how many connections are used, and how
often the query is called),
the query is executed in 1000ms, then 2000ms, and it continues to grow
exponentially. I've already
seen it reaching 80 seconds.

While having these time reports, I tried to query the database directly
using "psql", and I got the
same result (around 80 sec)

I compared this to an older version (7.0.2) of PostgreSQL, in the same
circumstances, and the worst
I had was a 4000ms, without going any further. That's why I suppose the
problem comes from the BETA
version.

----------
The query: (the ? are replaced by 'GPK', GPK being the key we want to look
for)
----------
SELECT quotes.xmldocument, prodrefs.xmldocument, orders.filteredorder,
responses.xmldocument
FROM quotes,prodrefs,responses,orders
WHERE quotes.negotiationGPK = ?
AND quotes.ctime = (SELECT MAX(ctime) FROM quotes WHERE
negotiationgpk = ?)
AND prodrefs.negotiationGPK = ?
AND orders.productreferenceGPK = prodrefs.gpk
AND owner=u1 AND overridden=FALSE
AND responses.orderGPK = orders.gpk
AND responses.ctime = (SELECT MAX(ctime) FROM responses WHERE
ordergpk=orders.gpk)
UNION
SELECT quotes.xmldocument,prodrefs.xmldocument,(''),('')
FROM quotes,prodrefs
WHERE quotes.negotiationGPK = ?
AND quotes.ctime = (SELECT MAX(ctime) FROM quotes WHERE
negotiationgpk = ?)
AND prodrefs.negotiationGPK = ?

-----------
The tables:
-----------
Table "quotes"
Attribute | Type | Modifier
----------------+-----------+----------
gpk | bigint | not null
xmldocument | text | not null
negotiationgpk | bigint | not null
ctime | timestamp | not null
Index: quotes_pkey

Table "prodrefs"
Attribute | Type | Modifier
----------------+-----------+----------
gpk | bigint | not null
ctime | timestamp | not null
xmldocument | text | not null
negotiationgpk | bigint | not null
Index: prodrefs_pkey

Table "orders"
Attribute | Type | Modifier
---------------------+-----------+----------
gpk | bigint | not null
ctime | timestamp | not null
productreferencegpk | bigint |
owner | text | not null
overridden | boolean |
overridingordergpk | bigint |
rawdata | text | not null
filteredorder | text | not null
previousquotegpk | bigint |
Index: orders_pkey

Table "responses"
Attribute | Type | Modifier
-------------+-----------+----------
gpk | bigint | not null
ctime | timestamp | not null
ordergpk | bigint |
xmldocument | text | not null
quotegpk | bigint |
Index: responses_pkey