![]() Here we basically double the amount of data written – all updated tables get a logging entry (including pgbench_accounts, which actually gets an insert already as part on normal transaction). Not too bad at all given we double the amount of data! Default pgbench vs 3 “logging insert” triggers By the way, to test how pgbench works with prepared statements (used mostly to test max IO throughput) set the “protocol” parameter to “prepared“. ![]() Important to note though – although were seeing some slowdown…it’s most probably still faster that doing that insert from the user transaction as we can space couple of network bytes + the parsing (in our default pgbench case statements are always re-parsed from text vs pl/pgsql code that are parsed only once (think “prepared statements”). So basically I was doing from the trigger the same as the insert portion (into pgbench_history) from the default pgbench transaction. Here things get a bit incomparable actually as we’re adding some new data, which is not there in the “un-triggered” version. Single row update with a trigger doing “logging insert” Rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc, Valbuf = (char*)SPI_getvalue(rettuple, tupdesc, attnum) The triggers will just set the last modification timestamp to current time and username to current user, if not already specified in the incoming row. This was the initial test that I ran for the original blog post – default pgbench transactions, with schema slightly modified to include 2 auditing columns for all tables being updated, doing 3 updates, 1 select, 1 insert (see here to see how the default transaction looks like) vs PL/PgSQL audit triggers on all 3 tables getting updates. Default pgbench vs audit triggers for all updated tables Please read on for some extra info on the performed tests or just jump to the concluding results table at end of article. So, to get more insights I conjured up some more complex trigger use cases and again measured transaction latencies on them for an extended period of time. But in which use cases would it make sense to start worrying a bit? The conclusion for the most common “audit fields” type of use case was that we should not worry about it too much and just create those triggers. SET X = (SELECT SUM(Y) FROM order_items WHERE order_id = NEW.In my last post I described what to expect from simple PL/pgSQL triggers in performance degradation sense, when doing some inspection/changing on the incoming row data. ![]() SET X = (SELECT SUM(Y) FROM order_items WHERE order_id = OLD.order_id) INSERT INTO order_items VALUES(11, 1, 30) ĬREATE OR REPLACE FUNCTION func_order_items() RETURNS trigger AS ![]() INSERT INTO order_items VALUES(10, 1, 20) If not, It raises an error ERROR: record "old" is not assigned yet.įinally, please take a look at the example as below: CREATE TABLE IF NOT EXISTS orders(ID INT NOT NULL PRIMARY KEY, X INT) ĬREATE TABLE IF NOT EXISTS order_items (ID INT NOT NULL PRIMARY KEY, ORDER_ID INT, Y INT) Secondly, please remember that you cannot have OLD when AFTER INSERT on the trigger. If not, It causes an error ERROR: function func_order_items must return type trigger. No arguments even if it expects to receive some arguments specified in Note that the function must be declared with How do I get the order_id from the original order_items table?įirstly, to create a trigger on the order_items table, the update_totals() must be a trigger function which RETURNS TRIGGER ( bold is mine).Ī data change trigger is declared as a function with no arguments andĪ return type of trigger. I tried creating a reference to the original table in the trigger: CREATE TRIGGER update_totals AFTER INSERTīut that just gives the error syntax error at or near "REFERENCING". When I try to run this, I get this error: missing FROM-clause for table "old" WHEN ( OLD.* IS DISTINCT FROM NEW.* ) EXECUTE PROCEDURE update_totals() Total_profit = (CASE WHEN total_cost IS NOT NULL THEN total - total_tax - total_cost - (SELECT SUM(fees) FROM order_items WHERE order_id = OLD.order_id) ELSE NULL END)ĬREATE TRIGGER update_totals AFTER INSERT Total_fees = (SELECT SUM(fees) FROM order_items WHERE order_id = OLD.order_id), This is what I have created: CREATE OR REPLACE FUNCTION update_totals() RETURNS void AS $$ I am trying to build a trigger function to automatically update parent order values any time any of it's items changes.
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