Thread: Issue in Improving the performance using prepared plan

CREATE OR REPLACE FUNCTION techdb_table_trigger()

  RETURNS trigger AS

$BODY$

our ($id, $query, $plan, $change_log_table);

 

$change_log_table = "ChangeLogTable";

 

$id = $_TD->{new}{'id'};

 

$query   = (<<ENDQUERY); 

    INSERT INTO $change_log_table(id)

    SELECT \$1

    EXCEPT SELECT id

    FROM $change_log_table

    WHERE id = \$1

    AND txid = txid_current()

    AND txtime = transaction_timestamp(); 

ENDQUERY

 

if (exists($_SHARED{$query})) {

   $plan  = $_SHARED{$query};

   elog(INFO, "########## Preparing the query ###########");  --> Always comes here. Don't know why?

} else {

   $plan  = spi_prepare($query, 'INTEGER');

   $_SHARED{$query} = $plan; 

   elog(INFO, "###############Using already prepared the query##############");  --> Never comes here.

}

 

spi_exec_prepared($plan, $id);

 

$BODY$

  LANGUAGE 'plperl' VOLATILE SECURITY DEFINER 

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> I have written following trigger and trying to improve the performance by
> using prepared query everytime. I have used spi_prepare to prepare the query
> and $_SHARED global hash to persist the prepared plan but it doesn't seem to
> work. Though $query will be same always in following trigger, it prepares
> query everytime and never uses prepared plan.
> Could anyone tell me what's wrong going on?

Works fine for me. Note that your elog outputs are switched - you are claiming
the already prepared plan for the first time (if exists) and claiming the
first prepare when in fact it is reusing (else).

- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation http://www.endpoint.com/
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