Re: Are there known performance issues with defining all Foreign Keys as deferrable initially immediate - Mailing list pgsql-performance

This seems under-documented and I haven't found much good info on it, so the best thing to do is test it.

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.


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Craig Ringer