Add backing off to auxilary workers

Author: mdellweg

CHANGES/+worker_backoff.feature

@@ -0,0 +1 @@
+Added backing off on auxiliary workers if wrongly alarmed on pending tasks.

pulpcore/tasking/entrypoint.py

@@ -34,7 +34,6 @@ def worker(
     auxiliary,
 ):
     """A Pulp worker."""
-
     if reload:
         try:
             import hupper

pulpcore/tasking/worker.py

@@ -2,6 +2,7 @@
 
 import functools
 import logging
+import math
 import os
 import random
 import select
@@ -89,9 +90,11 @@ def __init__(self, auxiliary=False):
         self.wakeup_unblock = False
         self.wakeup_handle = False
         self.cancel_task = False
+        self.unblocked_count = 0
 
         self.ignored_task_ids = []
         self.ignored_task_countdown = IGNORED_TASKS_CLEANUP_INTERVAL
+        self.false_alarms = 0
 
         self.auxiliary = auxiliary
         self.task = None
@@ -158,6 +161,14 @@ def _signal_handler(self, thesignal, frame):
         self.shutdown_requested = True
 
     def _pg_notify_handler(self, notification):
+        if notification.channel == "pulp_worker_broadcast":
+            key, value = notification.payload.split(":", maxsplit=1)
+            _logger.debug("broadcast message recieved: %s: %s", key, value)
+            if key == "unblocked_count":
+                self.unblocked_count = int(value)
+                self.wakeup_handle = self.unblocked_count > 0
+            elif key == "metrics_heartbeat":
+                self.last_metric_heartbeat = datetime.fromisoformat(key)
         if notification.channel == "pulp_worker_wakeup":
             if notification.payload == TASK_WAKEUP_UNBLOCK:
                 # Auxiliary workers don't do this.
@@ -171,6 +182,7 @@ def _pg_notify_handler(self, notification):
                 self.wakeup_handle = True
 
         elif notification.channel == "pulp_worker_metrics_heartbeat":
+            # TODO (in one of the next releases) Remove that superseeded channel.
             self.last_metric_heartbeat = datetime.fromisoformat(notification.payload)
         elif self.task and notification.channel == "pulp_worker_cancel":
             if notification.payload == str(self.task.pk):
@@ -257,6 +269,7 @@ def record_unblocked_waiting_tasks_metric(self, now):
         )
 
         self.cursor.execute(f"NOTIFY pulp_worker_metrics_heartbeat, '{str(now)}'")
+        self.broadcast("metrics_heartbeat", now)
 
     def beat(self):
         now = timezone.now()
@@ -278,6 +291,9 @@ def beat(self):
                 if self.otel_enabled and now > self.last_metric_heartbeat + self.heartbeat_period:
                     self.record_unblocked_waiting_tasks_metric(now)
 
+    def broadcast(self, key, value):
+        self.cursor.execute("SELECT pg_notify('pulp_worker_broadcast', %s)", (f"{key}:{value}",))
+
     def notify_workers(self, reason):
         self.cursor.execute("SELECT pg_notify('pulp_worker_wakeup', %s)", (reason,))
 
@@ -345,14 +361,17 @@ def unblock_tasks(self):
 
         self.wakeup_unblock = False
         result = self._unblock_tasks()
-        if result is not None and (
-            Task.objects.filter(
-                state__in=[TASK_STATES.WAITING, TASK_STATES.CANCELING], app_lock=None
+        if result is not None:
+            unblocked_count = (
+                Task.objects.filter(
+                    state__in=[TASK_STATES.WAITING, TASK_STATES.CANCELING], app_lock=None
+                )
+                .exclude(unblocked_at=None)
+                .count()
             )
-            .exclude(unblocked_at=None)
-            .exists()
-        ):
-            self.notify_workers(TASK_WAKEUP_HANDLE)
+            if unblocked_count > 0:
+                self.notify_workers(TASK_WAKEUP_HANDLE)
+                self.broadcast("unblocked_count", unblocked_count)
             return True
 
         return result
@@ -369,6 +388,7 @@ def _unblock_tasks(self):
             .order_by("pulp_created")
             .select_related("pulp_domain")
         ):
+            _logger.debug("Considering task %s for unblocking.", task.pk)
             reserved_resources_record = task.reserved_resources_record or []
             exclusive_resources = [
                 resource
@@ -389,23 +409,26 @@ def _unblock_tasks(self):
                     )
                     task.unblock()
 
-            elif (
-                task.state == TASK_STATES.WAITING
-                and task.unblocked_at is None
-                # No exclusive resource taken?
-                and not any(
-                    resource in taken_exclusive_resources or resource in taken_shared_resources
-                    for resource in exclusive_resources
-                )
-                # No shared resource exclusively taken?
-                and not any(resource in taken_exclusive_resources for resource in shared_resources)
-            ):
-                _logger.debug(
-                    "Marking waiting task %s in domain: %s unblocked.",
-                    task.pk,
-                    task.pulp_domain.name,
-                )
-                task.unblock()
+            elif task.state == TASK_STATES.WAITING and task.unblocked_at is None:
+                if (
+                    # No exclusive resource taken?
+                    not any(
+                        resource in taken_exclusive_resources or resource in taken_shared_resources
+                        for resource in exclusive_resources
+                    )
+                    # No shared resource exclusively taken?
+                    and not any(
+                        resource in taken_exclusive_resources for resource in shared_resources
+                    )
+                ):
+                    _logger.debug(
+                        "Marking waiting task %s in domain: %s unblocked.",
+                        task.pk,
+                        task.pulp_domain.name,
+                    )
+                    task.unblock()
+                else:
+                    _logger.debug("Task %s is still blocked.", task.pk)
             elif task.state == TASK_STATES.RUNNING and task.unblocked_at is None:
                 # This should not happen in normal operation.
                 # And it is only an issue if the worker running that task died, because it will
@@ -421,13 +444,14 @@ def _unblock_tasks(self):
             # Record the resources of the pending task
             taken_exclusive_resources.update(exclusive_resources)
             taken_shared_resources.update(shared_resources)
+        # raise Exception()
         return False
 
     def sleep(self):
         """Wait for signals on the wakeup channel while heart beating."""
 
-        _logger.debug(_("Worker %s entering sleep state."), self.name)
-        while not self.shutdown_requested and not self.wakeup_handle:
+        _logger.debug("Worker %s entering sleep state.", self.name)
+        while not self.shutdown_requested:
             r, w, x = select.select(
                 [self.sentinel, connection.connection],
                 [],
@@ -441,7 +465,15 @@ def sleep(self):
                 self.unblock_tasks()
             if self.sentinel in r:
                 os.read(self.sentinel, 256)
-        _logger.debug(_("Worker %s leaving sleep state."), self.name)
+            if self.wakeup_handle:
+                # There is probably a busy loop hidden here.
+                if not self.auxiliary or random.random() < math.exp(
+                    self.unblocked_count - self.false_alarms
+                ):
+                    _logger.debug("Worker %s leaving sleep state.", self.name)
+                    break
+                else:
+                    _logger.debug("Worker %s backing off", self.name)
 
     def supervise_task(self, task):
         """Call and supervise the task process while heart beating.
@@ -586,8 +618,12 @@ def handle_unblocked_tasks(self):
             task = self.fetch_task()
             if task is None:
                 # No task found
+                self.false_alarms += 1
+                _logger.debug("False Alarms: %s", self.false_alarms)
                 break
             try:
+                self.false_alarms //= 2
+                _logger.debug("False Alarms: %s", self.false_alarms)
                 if task.state == TASK_STATES.CANCELING:
                     # No worker picked this task up before being canceled.
                     # Or the worker disappeared before handling the canceling.
@@ -615,6 +651,7 @@ def run(self, burst=False):
             signal.signal(signal.SIGHUP, self._signal_handler)
             # Subscribe to pgsql channels
             connection.connection.add_notify_handler(self._pg_notify_handler)
+            self.cursor.execute("LISTEN pulp_worker_broadcast")
             self.cursor.execute("LISTEN pulp_worker_cancel")
             self.cursor.execute("LISTEN pulp_worker_metrics_heartbeat")
             if burst:
@@ -638,4 +675,5 @@ def run(self, burst=False):
                 self.cursor.execute("UNLISTEN pulp_worker_wakeup")
             self.cursor.execute("UNLISTEN pulp_worker_metrics_heartbeat")
             self.cursor.execute("UNLISTEN pulp_worker_cancel")
+            self.cursor.execute("UNLISTEN pulp_worker_broadcast")
             self.shutdown()