High Performance PostgreSQL for Rails

Automatically Gathering Execution Plans

To get plans automatically, we can use the PostgreSQL auto_explain module.

In the same way, you configured a minimum statement duration, which logged query text when queries exceeded that duration, auto_explain can log plans when a statement exceeds a certain duration.

auto_explain does add some overhead. Review the section that describes how “repeatedly reading the system clock can slow down queries” in the documentation.^[178]

Once you’ve determined the overhead is acceptable, start with a high value for your system, like one second, as the value for auto_explain.log_min_duration. This means that queries that take more than one second will have their execution plans logged to the postgresql.log.

When ...