Thread: Determining weather a query fired a trigger
I'm adding full text search to a CMS project after we upgraded to 8.3 of Postgres. I'd like to do a bit of testing before deploying it. I added columns to the pertinent tables for storing tsvectors, and was looking at my query code to update it so these columns get updated where appropriate when I discovered triggers as a solution to let this all happen in a way that's completely invisible and will require no rewriting of the existing queries. I set up triggers to fire on insert or update to do the job and it all seems to work fine. But I do have one concern regarding performance. The tsvector only needs to be updated if the title, summary, or keywords fields have changed. If they are the same after an update then there is no need to run them. Doing so would only cause a new tsvector to be generated when it wasn't necessary. So what I want to know is, is there a way to tell if executing a query caused a trigger to fire? I don't need anything fancy like notify and listen, I just want to see what the database is doing for testing purposes. For example by looking at the logs and seeing what activity was caused by a given query. Does this stuff get logged?
On Tue, Apr 08, 2008 at 07:03:07AM -0700, Gordon wrote: > But I do have one concern regarding performance. The tsvector only > needs to be updated if the title, summary, or keywords fields have > changed. If they are the same after an update then there is no need > to run them. Doing so would only cause a new tsvector to be generated > when it wasn't necessary. The usual trick is to check if the fields changed: IF OLD.title != NEW.title OR OLD.summary != NEW.summary OR ... THEN update_tsvector() END > So what I want to know is, is there a way to tell if executing a query > caused a trigger to fire? I don't need anything fancy like notify > and listen, I just want to see what the database is doing for testing > purposes. For example by looking at the logs and seeing what activity > was caused by a given query. Does this stuff get logged? You can access the string sent by the client, but that won't help you if the trigger was triggered within a stored procedure. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Please line up in a tree and maintain the heap invariant while > boarding. Thank you for flying nlogn airlines.
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Gordon wrote: > I'm adding full text search to a CMS project after we upgraded to 8.3 > of Postgres. I'd like to do a bit of testing before deploying it. > > I added columns to the pertinent tables for storing tsvectors, and was > looking at my query code to update it so these columns get updated > where appropriate when I discovered triggers as a solution to let this > all happen in a way that's completely invisible and will require no > rewriting of the existing queries. I set up triggers to fire on > insert or update to do the job and it all seems to work fine. > > But I do have one concern regarding performance. The tsvector only > needs to be updated if the title, summary, or keywords fields have > changed. If they are the same after an update then there is no need > to run them. Doing so would only cause a new tsvector to be generated > when it wasn't necessary. You'd normally do something like: IF (OLD.title IS DISTINCT FROM NEW.title) OR (OLD.body IS DISTINCT FROM NEW.body) THEN... That way you only update the tsvector if it's necessary. The "IS DISTINCT FROM" copes with NULLs. You still have the overhead of comparing old and new, but unless you have a very rapid rate of updates you'll be fine. > So what I want to know is, is there a way to tell if executing a query > caused a trigger to fire? I don't need anything fancy like notify > and listen, I just want to see what the database is doing for testing > purposes. For example by looking at the logs and seeing what activity > was caused by a given query. Does this stuff get logged? Closest I can think is to check the pg_stat_xxx views and tables. That will show you how many rows are accessed/updated on what tables. -- Richard Huxton Archonet Ltd
Gordon wrote: > > So what I want to know is, is there a way to tell if executing a query > caused a trigger to fire? I don't need anything fancy like notify > and listen, I just want to see what the database is doing for testing > purposes. For example by looking at the logs and seeing what activity > was caused by a given query. Does this stuff get logged? > If you can modify the trigger and it's written in PL/PgSQL you can use a `RAISE NOTICE' statement to log some information when the trigger fires. Those are several big "if"s though. -- Craig Ringer