Add log to analyze FuzzTargetJob entity deletion (#5051)

The cleanup cronjob is failing for Internal due to a `FuzzTargetJob`
query timeout, and the discussion in b/418807403 indicates that the
issue may be related to the deletion of `FuzzTargetJob` entities. This
PR adds a log to help confirm if deletion is the main problem, which
will be useful for developing an appropriate solution.

Key changes:
- Added a log to indicate how many `FuzzTargetJob` entities are deleted
per cronjob and how many remain in the database.
- Transformed the query iterator into a list to log the remaining
entities. This may increase memory usage, but it should not be a problem
as this kind has around 5,000 entities.

Related to b/418807403 and b/406250205.

Author: decoNR

src/clusterfuzz/_internal/cron/cleanup.py

@@ -208,18 +208,28 @@ def cleanup_unused_fuzz_targets_and_jobs():
   unused_target_jobs = data_types.FuzzTargetJob.query(
       data_types.FuzzTargetJob.last_run < last_run_cutoff)
   # The order by last_run DESC filter is from b/418807403
-  valid_target_jobs = data_types.FuzzTargetJob.query(
-      data_types.FuzzTargetJob.last_run >= last_run_cutoff).order(
-          -data_types.FuzzTargetJob.last_run)
+  valid_target_jobs = list(
+      data_types.FuzzTargetJob.query(
+          data_types.FuzzTargetJob.last_run >= last_run_cutoff).order(
+              -data_types.FuzzTargetJob.last_run))
 
   to_delete = [t.key for t in unused_target_jobs]
+  num_fuzz_target_jobs_to_delete = len(to_delete)
+
+  logs.info(
+      f'{len(to_delete)} FuzzTargetJob entities are marked for deletion and'
+      f'{len(valid_target_jobs)} are considered valid.')
 
   valid_fuzz_targets = {t.fuzz_target_name for t in valid_target_jobs}
   for fuzz_target in ndb_utils.get_all_from_model(data_types.FuzzTarget):
     if fuzz_target.fully_qualified_name() not in valid_fuzz_targets:
       to_delete.append(fuzz_target.key)
 
   ndb_utils.delete_multi(to_delete)
+  logs.info(
+      f'Deleted {num_fuzz_target_jobs_to_delete} FuzzTargetJob entities and '
+      f'{len(to_delete) - num_fuzz_target_jobs_to_delete} FuzzTarget entities. '
+      f'{len(valid_target_jobs)} valid FuzzTargetJob entities remain.')
 
 
 def get_jobs_and_platforms_for_project():

src/clusterfuzz/_internal/datastore/data_handler.py

@@ -1775,7 +1775,7 @@ def record_fuzz_targets(engine_name, binaries, job_type):
   jobs = get_or_create_multi_entities_from_keys(job_mapping)
 
   for job in jobs:
-    # TODO(metzman): Decide if we want to handle unused fuzzers differentlyo.
+    # TODO(metzman): Decide if we want to handle unused fuzzers differently.
     job.last_run = utils.utcnow()
 
   ndb_utils.put_multi(jobs)