Poor Performance after Upgrade - Mailing list pgsql-performance

Hi,

I recently inherited a very old (PostgreSQL 7.0.3) database, and have
migrated it to 8.2.4 but have run into a performance issue.

Basically, I did a dump and import into the new database, vacuumed and
created fresh indexes and everything is work great except the following
type of query (and similar):

  SELECT tsr.stepId, tsr.testType, tsr.problemReportId, tsr.excpt, tcr.caseId
     FROM   TestCaseRun tcr, TestStepRun tsr
     WHERE  tcr.parentSN = 194813
     AND    (tsr.testType        <> ''
     OR      tsr.problemReportId <> ''
     OR      tsr.excpt           <> '')
     AND    tsr.parentSN =  tcr.recordSN

What used to take 250ms or so on the old database now takes between 55 and
60 Seconds.

On the old database, the query plan looks like this:

Unique  (cost=13074.30..13078.36 rows=32 width=68)
   ->  Sort  (cost=13074.30..13074.30 rows=324 width=68)
         ->  Nested Loop  (cost=0.00..13060.77 rows=324 width=68)
               ->  Index Scan using parentsn_tcr_indx on testcaserun tcr
(cost=0.00..444.83 rows=111 width=16)
               ->  Index Scan using parentsn_tsr_indx on teststeprun tsr
(cost=0.00..113.42 rows=27 width=52)

And on the new database it looks like this:

  Unique  (cost=206559152.10..206559157.14 rows=336 width=137)
    ->  Sort  (cost=206559152.10..206559152.94 rows=336 width=137)
          Sort Key: tsr.stepid, tsr.testtype, tsr.problemreportid,
tsr.excpt, tcr.caseid
          ->  Nested Loop  (cost=100000000.00..106559138.00 rows=336
width=137)
                ->  Index Scan using parentsn_tcr_indx on testcaserun tcr
(cost=0.00..17.00 rows=115 width=11)
                      Index Cond: (parentsn = 186726)
                ->  Index Scan using parentsn_tsr_indx on teststeprun tsr
(cost=0.00..56089.00 rows=75747 width=134)
                      Index Cond: (tsr.parentsn = tcr.recordsn)
                      Filter: ((testtype <> ''::text) OR
((problemreportid)::text <> ''::text) OR (excpt <> ''::text))
(9 rows)

I'm fairly familiar with PostgreSQL, but I have no idea where to start in
trying to trouble shoot this huge performance discrepancy. The hardware
and OS are the same.

And the data size is exactly the same between the two, and the total data
size is about 7.5GB, with the largest table (teststeprun mentioned above)
being about 15 million rows.

Any pointers to where to start troubleshooting this or how to change the
query to work better would be appreciated.

cheers and thanks,
Ben Perrault
Sr. Systems Consultant
Alcatel-Lucent Internetworking