Re: Strange discrepancy in query performance...

["Jason L. Buberel" <jason@xxxxxxxxxxx>]

Tom-right-as-usual:

Yep - you were right about the query plan for the prepared statement (a sequential scan of the table) differed a bit from the directly-executed version :)

For reference, when using JasperReports .jrxml files as the basis for the query, I only had to do to the following to 'force' postgres to treat the jasper report parameter as a number and not text, thereby allowing the correct index to be used:

select * from city summary where city_master_id = $P{city_master_id}::bigint ...

Query times went from 300+ seconds back down to ~100ms.

-jason

Tom Lane wrote:

"Jason L. Buberel" <jason@xxxxxxxxxxx> writes:
  

In my syslog output, I see entries indicating that the 
JDBC-driver-originated query on a table named 'city_summary' are taking 
upwards of 300 seconds:
    

Oct  1 18:27:47 srv3 postgres-8.2[1625]: [12-1]
LOG:  duration: 307077.037 ms  execute S_42: select * from city_summary
      where  state = $1 and city_master_id = $2 and res_type = 
'single_family' and date = $3
      and range = 90 and zip = $4 and quartile  = '__ALL'
DETAIL:  parameters: $1 = 'CA', $2 = '291', $3 = '2007-09-28', $4 = '__ALL'
    

However, if I run the same query on the same host at the same time that 
the Java application is running, but from the psql  command line, it 
takes only 0.37 seconds:
    

time /opt/postgres-8.2.4/bin/psql --port 54824  -U postgres -d 
        

altos_research  -c 'select fact_id from city_summary where state = 
\'CA\' and city_master_id = 291 and zip = \'__ALL\' and quartile = 
\'__ALL\' and res_type = \'single_family\' and range = \'90\' and date = 
\'2007-09-28\';'
    

This is not, in fact, the same query --- the JDBC-originated one is
parameterized, which means it very possibly has a different plan
(since the planner doesn't know the particular values to plan for).

Try using PREPARE and EXPLAIN EXECUTE to examine the plan that is
being produced for the parameterized query.

			regards, tom lane