Keep Transactions Short to Reduce Lock Contention#
Long-running transactions hold locks that block other queries. Keep transactions as short as possible.
Incorrect (long transaction with external calls):
begin;
select * from orders where id = 1 for update; -- Lock acquired
-- Application makes HTTP call to payment API (2-5 seconds)
-- Other queries on this row are blocked!
update orders set status = 'paid' where id = 1;
commit; -- Lock held for entire duration
Correct (minimal transaction scope):
-- Validate data and call APIs outside transaction
-- Application: response = await paymentAPI.charge(...)
-- Only hold lock for the actual update
begin;
update orders
set status = 'paid', payment_id = $1
where id = $2 and status = 'pending'
returning *;
commit; -- Lock held for milliseconds
Use statement_timeout to prevent runaway transactions:
-- Abort queries running longer than 30 seconds
set statement_timeout = '30s';
-- Or per-session
set local statement_timeout = '5s';
Reference: Transaction Management