On 10/15/2014 02:39 PM, Jonathan Rogers wrote:
I was just reading the PL/Python docs section "42.7.1 Database Access Functions" and saw this example:CREATE FUNCTION usesavedplan() RETURNS trigger AS $$ plan = SD.setdefault("plan", plpy.prepare("SELECT 1")) # rest of function $$ LANGUAGE plpythonu; The above example uses the plpy.prepare() function, reusing the result across function calls uses setdefault(). Unfortunately, since setdefault() is a method on dict objects, the values passed to it must be evaluated before it can be called. Therefore, plpy.prepare() will be called every time usesavedplan() executes whether a result already exists in the SD dict or not. I'm not sure if it's a problem that plpy.prepare() is called every time since the result is discarded if a prepared statement had been cached by a previous execution of usesavedplan(). It seems that some wasted processing will occur, but maybe not enough to matter. The documentation for SPI_prepare() does not clearly state what tasks that function performs other than constructing a prepared statement object. It seems to imply that parsing does occur within SPI_prepare(). It does state that query planning occurs within SPI_execute_plan(). Can anyone clarify what occurs when plpy.prepare() is called? Is it worth using a Python conditional to determine whether to call it rather than using SD.setdefault()?
Like in the older documentation?: http://www.postgresql.org/docs/9.1/static/plpython-database.html CREATE FUNCTION usesavedplan() RETURNS trigger AS $$ if SD.has_key("plan"): plan = SD["plan"] else: plan = plpy.prepare("SELECT 1") SD["plan"] = plan # rest of function $$ LANGUAGE plpythonu;
-- Adrian Klaver adrian.kla...@aklaver.com -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
