Re: joining two tables slow due to sequential scan - Mailing list pgsql-performance

oops

QUERY PLAN
'Hash Join  (cost=899.83..4384.17 rows=482 width=1350) (actual
time=0.203..0.203 rows=0 loops=1)'
'  Hash Cond: ("outer".documentidentifier =
"inner".dssdocumentidentifier)'
'  ->  Seq Scan on documentversions  (cost=0.00..2997.68 rows=96368
width=996) (actual time=0.007..0.007 rows=1 loops=1)'
'  ->  Hash  (cost=898.62..898.62 rows=482 width=354) (actual
time=0.161..0.161 rows=0 loops=1)'
'        ->  Bitmap Heap Scan on clinicaldocuments  (cost=4.69..898.62
rows=482 width=354) (actual time=0.159..0.159 rows=0 loops=1)'
'              Recheck Cond: (patientidentifier = 123)'
'              ->  Bitmap Index Scan on ix_cdocpid  (cost=0.00..4.69
rows=482 width=0) (actual time=0.153..0.153 rows=0 loops=1)'
'                    Index Cond: (patientidentifier = 123)'
'Total runtime: 0.392 ms'

note I have done these on a smaller db than what I am using but the
plans are the same


Tim Jones
Healthcare Project Manager
Optio Software, Inc.
(770) 576-3555

-----Original Message-----
From: Scott Marlowe [mailto:smarlowe@g2switchworks.com]
Sent: Friday, February 10, 2006 5:39 PM
To: Tim Jones
Cc: Dave Dutcher; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] joining two tables slow due to sequential scan

On Fri, 2006-02-10 at 16:37, Tim Jones wrote:
> for first query
>
> QUERY PLAN
> 'Limit  (cost=4.69..88.47 rows=10 width=1350) (actual
> time=32.195..32.338 rows=10 loops=1)'
> '  ->  Nested Loop  (cost=4.69..4043.09 rows=482 width=1350) (actual
> time=32.190..32.316 rows=10 loops=1)'
> '        ->  Bitmap Heap Scan on documentversions  (cost=4.69..1139.40
> rows=482 width=996) (actual time=32.161..32.171 rows=10 loops=1)'
> '              Recheck Cond: (documentstatus = ''AC''::bpchar)'
> '              ->  Bitmap Index Scan on ix_docstatus  (cost=0.00..4.69
> rows=482 width=0) (actual time=31.467..31.467 rows=96368 loops=1)'
> '                    Index Cond: (documentstatus = ''AC''::bpchar)'
> '        ->  Index Scan using ix_cdocdid on clinicaldocuments
> (cost=0.00..6.01 rows=1 width=354) (actual time=0.006..0.007 rows=1
> loops=10)'
> '              Index Cond: ("outer".documentidentifier =
> clinicaldocuments.dssdocumentidentifier)'
>
>
>  for second query
>
> QUERY PLAN
> 'Hash Join  (cost=899.83..4384.17 rows=482 width=1350)'
> '  Hash Cond: ("outer".documentidentifier =
> "inner".dssdocumentidentifier)'
> '  ->  Seq Scan on documentversions  (cost=0.00..2997.68 rows=96368
> width=996)'
> '  ->  Hash  (cost=898.62..898.62 rows=482 width=354)'
> '        ->  Bitmap Heap Scan on clinicaldocuments  (cost=4.69..898.62
> rows=482 width=354)'
> '              Recheck Cond: (patientidentifier = 123)'
> '              ->  Bitmap Index Scan on ix_cdocpid  (cost=0.00..4.69
> rows=482 width=0)'
> '                    Index Cond: (patientidentifier = 123)'

OK, the first one is explain analyze, but the second one is just plain
explain...