[couchdb] branch replicator-job-churn-fix updated (036ade3 -> c34b417)

[va...@apache.org]

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 discard 036ade3  Avoid churning replication jobs if there is enough room to run pending jobs
     new c34b417  Avoid churning replication jobs if there is enough room to run pending jobs

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Summary of changes:
 src/couch_replicator/src/couch_replicator_scheduler.erl | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

[couchdb] 01/01: Avoid churning replication jobs if there is enough room to run pending jobs

[va...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

vatamane pushed a commit to branch replicator-job-churn-fix
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit c34b417d6f4ace0fdad8438127ebc99791b4d70e
Author: Nick Vatamaniuc <va...@apache.org>
AuthorDate: Tue Oct 22 14:27:13 2019 -0400

    Avoid churning replication jobs if there is enough room to run pending jobs
    
    When rescheduling jobs, make sure to stops existing job as much as needed to
    make room for the pending jobs.
---
 .../src/couch_replicator_scheduler.erl             | 38 ++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/src/couch_replicator/src/couch_replicator_scheduler.erl b/src/couch_replicator/src/couch_replicator_scheduler.erl
index 7fe417a..0e60fed 100644
--- a/src/couch_replicator/src/couch_replicator_scheduler.erl
+++ b/src/couch_replicator/src/couch_replicator_scheduler.erl
@@ -760,8 +760,12 @@ rotate_jobs(State, ChurnSoFar) ->
     % Reduce MaxChurn by the number of already stopped jobs in the
     % current rescheduling cycle.
     Churn = max(0, MaxChurn - ChurnSoFar),
-    if Running =< MaxJobs ->
-        StopCount = lists:min([Pending, Running, Churn]),
+    SlotsAvailable = MaxJobs - Running,
+    if SlotsAvailable >= 0 ->
+        % If there is are enough SlotsAvailable reduce StopCount to avoid
+        % unnesessarily stopping jobs. `stop_jobs/3` ignores 0 or negaive
+        % values so we don't worry about that here.
+        StopCount = lists:min([Pending - SlotsAvailable, Running, Churn]),
         stop_jobs(StopCount, true, State),
         StartCount = max(0, MaxJobs - running_job_count()),
         start_jobs(StartCount, State);
@@ -1047,6 +1051,8 @@ scheduler_test_() ->
             t_stop_oldest_first(),
             t_start_oldest_first(),
             t_jobs_churn_even_if_not_all_max_jobs_are_running(),
+            t_jobs_dont_churn_if_there_are_available_running_slots(),
+            t_start_only_pending_jobs_do_not_churn_existing_ones(),
             t_dont_stop_if_nothing_pending(),
             t_max_churn_limits_number_of_rotated_jobs(),
             t_existing_jobs(),
@@ -1207,11 +1213,39 @@ t_jobs_churn_even_if_not_all_max_jobs_are_running() ->
             continuous(5)
         ]),
         reschedule(mock_state(2, 2)),
+        % 7 would stop running and 2 and 5 will start since they will be the
+        % oldest pending jobs
         ?assertEqual({2, 1}, run_stop_count()),
         ?assertEqual([7], jobs_stopped())
     end).
 
 
+t_jobs_dont_churn_if_there_are_available_running_slots() ->
+     ?_test(begin
+        setup_jobs([
+            continuous_running(1),
+            continuous_running(2)
+        ]),
+        reschedule(mock_state(2, 2)),
+        ?assertEqual({2, 0}, run_stop_count()),
+        ?assertEqual([], jobs_stopped()),
+        ?assertEqual(0, meck:num_calls(couch_replicator_scheduler_sup, start_child, 1))
+    end).
+
+
+t_start_only_pending_jobs_do_not_churn_existing_ones() ->
+     ?_test(begin
+        setup_jobs([
+            continuous(1),
+            continuous_running(2)
+        ]),
+        reschedule(mock_state(2, 2)),
+        ?assertEqual(1, meck:num_calls(couch_replicator_scheduler_sup, start_child, 1)),
+        ?assertEqual([], jobs_stopped()),
+        ?assertEqual({2, 0}, run_stop_count())
+    end).
+
+
 t_dont_stop_if_nothing_pending() ->
     ?_test(begin
         setup_jobs([continuous_running(1), continuous_running(2)]),