[vox-tech] querying postgres from php

[Henry House]

P=E5 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 a=
bout =

> 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 =3D db_handle.prepare("select foo from bar where foo =3D ?=
")
result1 =3D statement_handle.execute(statement_handle, "a")
result2 =3D statement_handle.execute(statement_handle, "b")
result3 =3D statement_handle.execute(statement_handle, "c")

which is equivalent to:

result1 =3D db_handle.execute("select foo from bar where foo =3D 'a'")
result2 =3D db_handle.execute("select foo from bar where foo =3D 'b'")
result3 =3D db_handle.execute("select foo from bar where foo =3D '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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