Craig Ringer <ringerc@xxxxxxxxxxxxx> writes: > Found it, it's in the NOTES for CREATE TABLE. > http://www.postgresql.org/docs/current/static/sql-createtable.html: > When a UNIQUE or PRIMARY KEY constraint is not deferrable, PostgreSQL > checks for uniqueness immediately whenever a row is inserted or > modified. The SQL standard says that uniqueness should be enforced only > at the end of the statement; this makes a difference when, for example, > a single command updates multiple key values. To obtain > standard-compliant behavior, declare the constraint as DEFERRABLE but > not deferred (i.e., INITIALLY IMMEDIATE). Be aware that this can be > significantly slower than immediate uniqueness checking. Note that that is addressing uniqueness constraints, and *only* uniqueness constraints. Foreign key constraints are implemented differently. There is no equivalent to an immediate check of a foreign key constraint --- it's checked either at end of statement or end of transaction, depending on the DEFERRED property. So there's really no performance difference for FKs, unless you let a large number of pending checks accumulate over multiple commands within a transaction. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
