High Performance PostgreSQL for Rails

Monitoring Row Locks

For general query logging from errors, try setting the log_min_error_statement^[285] parameter. This logs queries to the postgresql.log file when they’re blocked. Another more targeted option is the log_lock_waits parameter, which you’ll see in an upcoming section.

One gotcha to be aware of is mentioned in the post “Selecting for Share and Update in PostgreSQL.”^[286] When using SELECT...FOR UPDATE, referenced tables from foreign key columns will also be locked from SELECT...FOR UPDATE. This behavior is necessary to maintain referential integrity.

When that’s too onerous, a weaker type of lock is SELECT...FOR SHARE. This lock type creates a shared lock on the rows being selected. A shared lock allows concurrent reads for ...