[couchdb] branch master updated: Avoid churning replication jobs if there is enough room to run pending jobs

[va...@apache.org]

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vatamane pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/couchdb.git


The following commit(s) were added to refs/heads/master by this push:
     new 79cfc1d  Avoid churning replication jobs if there is enough room to run pending jobs
79cfc1d is described below

commit 79cfc1df5e5e8e0d495bc58187306e8f7bfe06dc
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             | 36 ++++++++++++++++++++--
 1 file changed, 34 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..52d362b 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 negative
+        % 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(),
@@ -1212,6 +1218,32 @@ t_jobs_churn_even_if_not_all_max_jobs_are_running() ->
     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)]),