Prioritizing Blocked Code

pglock.prioritize ensures that any blocking locks of a piece of code will be terminated. A background thread carries out termination of blocking statements on a configurable periodic interval.

Basic Usage

For example, below we've ensured that our function kills any blocking activity during its execution:

import pglock

@pglock.prioritize()
def my_important_function():
    # If any statements block this function, they will be terminated.

By default, the background thread operations on a one-second interval, but this can be configured with the interval argument:

@pglock.prioritize(interval=5)
def my_important_function():
    # Every five seconds, blocking activity will be terminated

Tip

Use a datetime.timedelta object for the interval for more precision.

Side Effects

The side_effect argument can be used to configure the function executed by the background worker. It defaults to pglock.Terminate, which terminates all blocking queries.

pglock.Terminate can be supplied filters that are applied to the underlying pglock.models.BlockedPGLock queryset. For example, the following will terminate blocking queries that have a duration greater than five seconds:

@pglock.prioritize(
    side_effect=pglock.Terminate(blocking_activity__duration__gte="5 seconds")
)
def my_important_function():
    # Blocking activity with a duration greater than five seconds will
    # be terminated

Underneath the hood, side effects are supplied a pglock.models.BlockedPGLock queryset that has filters applied. Side effects inherit pglock.PrioritizeSideEffect and implement the worker method. The pglock.Terminate side effect looks like this:

class Terminate(pglock.PrioritizeSideEffect):
    def worker(self, blocked_locks):
        return blocked_locks.terminate_blocking_activity()

If you don't want to terminate processes, you can use pglock.prioritize(side_effect=pglock.Cancel) to cancel blocking activity; however, keep in mind that some queries are not able to be canceled and the prioritized process may continue to be blocked.