From: Howard Cole <howardnews@selestial.com>
To: pgsql-performance@postgresql.org
Subject: Re: Tsearch2 Initial Search Speed
Date: Tue, 17 Jun 2008 11:54:12 +0100
Message-ID: <485797D4.7010201@selestial.com> (raw)
In-Reply-To: <485789C1.3000803@selestial.com>
References: <4856A91F.1020001@selestial.com>
<200806161124.57543@hal.medialogik.com>
<485789C1.3000803@selestial.com>
I think I may have answered my own question partially, the problem may
be how I structure the query.
I always structured my tsearch queries as follows following my initial
read of the tsearch2 instructions...
select email_id from email, to_tsquery('default', 'howard') as q where
q@@fts;
However if I construct them in the following way, as stipulated in the
8.3 documentation....
select email_id from email where fts@@to_tsquery('default','howard')
Then the results are better due to the fact that the email table is not
necessarily scanned as can be seen from the two analyse statements:
Original statement:
"Nested Loop (cost=4.40..65.08 rows=16 width=8)"
" -> Function Scan on q (cost=0.00..0.01 rows=1 width=32)"
" -> Bitmap Heap Scan on email (cost=4.40..64.87 rows=16 width=489)"
" Filter: (email.fts @@ q.q)"
" -> Bitmap Index Scan on email_fts_index (cost=0.00..4.40
rows=16 width=0)"
" Index Cond: (email.fts @@ q.q)"
Second statement:
"Bitmap Heap Scan on email (cost=4.40..64.91 rows=16 width=8)"
" Filter: (fts @@ '''howard'''::tsquery)"
" -> Bitmap Index Scan on email_fts_index (cost=0.00..4.40 rows=16
width=0)"
" Index Cond: (fts @@ '''howard'''::tsquery)"
This misses out the random access of the email table, turning my 27
second query into 6 seconds.
I guess the construction of the first statement effectively stops the
query optimisation from working.
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To: pgsql-performance@postgresql.org
Cc: howardnews@selestial.com
Subject: Re: Tsearch2 Initial Search Speed
In-Reply-To: <485797D4.7010201@selestial.com>
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