Re: [PERFORM] Index not used with prepared statement
On 11.09.2005, at 11:03 Uhr, Andreas Seltenreich wrote: I'm not perfectly sure, but since the index could only be used with a subset of all possible parameters (the pattern for like has to be left-anchored), I could imagine the planner has to avoid the index in order to produce an universal plan (the thing behind a prepared statement). Hmm. Now I get it. So I have to look that my framework doesn't produce a preparedStatement, instead build a complete statement string. Weird. Is there a reason you are using the like operator at all? IMO using the =-operator instead in your example should produce an "index-using prepared statement". Yes, you are right, but then I can't pass anything like '45%' to the query. It will just return nothing. I use the "like" because I build the queries on the fly and add a % at the end where necessary. And, to be clear: this is a minimal example, most of my queries are generated by a framework. This was an example to test the behaviour. Okay, I had problems with the understanding of prepared statements on the client and the server side. What I thought was, that I get a preparedStatement by JDBC which also inserts the values into the string and this is executed on the server side. cug ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PERFORM] Index not used with prepared statement
Guido Neitzer schrob:
> I have a performance problem with prepared statements (JDBC prepared
> statement).
>
> This query:
>
> PreparedStatement st = conn.prepareStatement("SELECT id FROM
> dga_dienstleister WHERE plz like '45257'");
>
> does use an index.
>
> This query:
>
> String plz = "45257";
> PreparedStatement st = conn.prepareStatement("SELECT id FROM
> dga_dienstleister WHERE plz like ?");
> st.setString(1, plz);
>
> does NOT use an index.
>
> As it should in the end result in absolutely the same statement, the
> index should be used all the time.
I'm not perfectly sure, but since the index could only be used with a
subset of all possible parameters (the pattern for like has to be
left-anchored), I could imagine the planner has to avoid the index in
order to produce an universal plan (the thing behind a prepared
statement).
Is there a reason you are using the like operator at all? IMO using
the =-operator instead in your example should produce an "index-using
prepared statement".
HTH
Andreas
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[PERFORM] Index not used with prepared statement
Hi.
I have a performance problem with prepared statements (JDBC prepared
statement).
This query:
PreparedStatement st = conn.prepareStatement("SELECT id FROM
dga_dienstleister WHERE plz like '45257'");
does use an index.
This query:
String plz = "45257";
PreparedStatement st = conn.prepareStatement("SELECT id FROM
dga_dienstleister WHERE plz like ?");
st.setString(1, plz);
does NOT use an index.
As it should in the end result in absolutely the same statement, the
index should be used all the time. I have to set the
protocolVersion=2 and use the JDBC2 driver to get it working (but
then the statements are created like in the first query, so no
solution, only a workaround).
I'm not sure whether this is a bug (I think it is) or a problem of
understanding.
Known problem?
I have tried PG 8.0.1, 8.0.3, 8.1beta with the JDBC-drivers
- postgresql-8.0-312.jdbc2.jar --> okay with protocolVersion=2 in the
URL
- postgresql-8.0-312.jdbc3.jar --> not okay whatever I do
I'm on Mac OS X, if that matters.
cug
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