Re: [vox-tech] querying postgres from php

[MAPShajhouse@houseag.com (Henry House)]

På 2006-11-14, skrev Dylan Beaudette:
> Hi everyone,
> 
> i have a large postgres table, that i am querying from php: specifically:
> 
> 1. query the rule classes associated with a given ID
> 2. query for a set of rules within a given class
> 3. for each rule, query the reasons why that rule is enforced 
> 
> this results in about 60 'select ...' statements. Watching the queries as they 
> are run from pgtop, i notice that they run serially and not all that fast.
> 
> Running the same set of queries from the psql command line client takes about 
> 5 seconds max. Therefore, I think that the problem may be in the overhead 
> involved in executing each query- or some PHP/Apache thing. I have a full set 
> of indices built on this table, and using 'explain query ...' yields no 'seq 
> scans', suggesting (i think) efficient use of the indices.
> 
> Any thoughts on how one might approach this issue ? 

I am assuming that you have already tried to combine the about 60
queries into a smaller number of queries and that there is a good reason
why this can't be done.

My initial though is to try preparing the queries with placeholders for
their specific parameters prior to execution. I don't know anything
about database access in PHP, but in Perl and Ruby you can do something
like this (pseudocode, not actually runnable):

statement_handle = db_handle.prepare("select foo from bar where foo = ?")
result1 = statement_handle.execute(statement_handle, "a")
result2 = statement_handle.execute(statement_handle, "b")
result3 = statement_handle.execute(statement_handle, "c")

which is equivalent to:

result1 = db_handle.execute("select foo from bar where foo = 'a'")
result2 = db_handle.execute("select foo from bar where foo = 'b'")
result3 = db_handle.execute("select foo from bar where foo = 'c'")

The former case should be faster as it allows the database engine (if so
designed) to re-use the same query plan for the same logistically
equivalent queries.

-- 
Henry House
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