Retain replication stats between job runs

Previously stats counts between job runs were reset. So if a job was stopped
and restarted by the scheduler, its docs_written, docs_read, doc_write_failures,
etc., counts would go back to 0. For doc_write_failures this was especially bad
as it hid the fact that some documents were not replicated to the target
because either a VDU failed or one of the limits were hit.

This change preserves stats across job runs. Everytime active tasks is updated,
the stats object in rep record of each job in scheduler's ets table will be
updated asynchronously. On next job start the job will reinitialize from last
saved stats.

Relates somewhat to issue #1159

4 files changed, 190 insertions, 13 deletions

diff --git a/src/couch_replicator/src/couch_replicator.hrl b/src/couch_replicator/src/couch_replicator.hrl
index d46c34720..2a5b7c8c8 100644
--- a/src/couch_replicator/src/couch_replicator.hrl
+++ b/src/couch_replicator/src/couch_replicator.hrl
@@ -22,7 +22,8 @@
     view = nil :: any() | '_',
     doc_id :: any() | '_',
     db_name = null :: null | binary() | '_',
-    start_time = {0, 0, 0} :: erlang:timestamp() | '_'
+    start_time = {0, 0, 0} :: erlang:timestamp() | '_',
+    stats = couch_replicator_stats:new() :: orddict:orddict() | '_'
 }).
 
 -type rep_id() :: {string(), string()}.
diff --git a/src/couch_replicator/src/couch_replicator_scheduler.erl b/src/couch_replicator/src/couch_replicator_scheduler.erl
index 762ef18fe..e3dbede83 100644
--- a/src/couch_replicator/src/couch_replicator_scheduler.erl
+++ b/src/couch_replicator/src/couch_replicator_scheduler.erl
@@ -40,7 +40,8 @@
    health_threshold/0,
    jobs/0,
    job/1,
-   restart_job/1
+   restart_job/1,
+   update_job_stats/2
 ]).
 
 %% config_listener callbacks
@@ -215,6 +216,11 @@ restart_job(JobId) ->
     end.
 
 
+-spec update_job_stats(job_id(), term()) -> ok.
+update_job_stats(JobId, Stats) ->
+    gen_server:cast(?MODULE, {update_job_stats, JobId, Stats}).
+
+
 %% gen_server functions
 
 init(_) ->
@@ -283,6 +289,16 @@ handle_cast({set_interval, Interval}, State) when is_integer(Interval),
     couch_log:notice("~p: interval set to ~B", [?MODULE, Interval]),
     {noreply, State#state{interval = Interval}};
 
+handle_cast({update_job_stats, JobId, Stats}, State) ->
+    case rep_state(JobId) of
+        nil ->
+            ok;
+        #rep{} = Rep ->
+            NewRep = Rep#rep{stats = Stats},
+            true = ets:update_element(?MODULE, JobId, {#job.rep, NewRep})
+    end,
+    {noreply, State};
+
 handle_cast(UnexpectedMsg, State) ->
     couch_log:error("~p: received un-expected cast ~p", [?MODULE, UnexpectedMsg]),
     {noreply, State}.
diff --git a/src/couch_replicator/src/couch_replicator_scheduler_job.erl b/src/couch_replicator/src/couch_replicator_scheduler_job.erl
index 1467d9f30..f669d464d 100644
--- a/src/couch_replicator/src/couch_replicator_scheduler_job.erl
+++ b/src/couch_replicator/src/couch_replicator_scheduler_job.erl
@@ -118,7 +118,6 @@ do_init(#rep{options = Options, id = {BaseId, Ext}, user_ctx=UserCtx} = Rep) ->
         source_name = SourceName,
         target_name = TargetName,
         start_seq = {_Ts, StartSeq},
-        committed_seq = {_, CommittedSeq},
         highest_seq_done = {_, HighestSeq},
         checkpoint_interval = CheckpointInterval
     } = State = init_state(Rep),
@@ -159,16 +158,9 @@ do_init(#rep{options = Options, id = {BaseId, Ext}, user_ctx=UserCtx} = Rep) ->
         {source, ?l2b(SourceName)},
         {target, ?l2b(TargetName)},
         {continuous, get_value(continuous, Options, false)},
-        {revisions_checked, 0},
-        {missing_revisions_found, 0},
-        {docs_read, 0},
-        {docs_written, 0},
-        {changes_pending, get_pending_count(State)},
-        {doc_write_failures, 0},
         {source_seq, HighestSeq},
-        {checkpointed_source_seq, CommittedSeq},
         {checkpoint_interval, CheckpointInterval}
-    ]),
+    ] ++ rep_stats(State)),
     couch_task_status:set_update_frequency(1000),
 
     % Until OTP R14B03:
@@ -582,7 +574,8 @@ init_state(Rep) ->
         source = Src0, target = Tgt,
         options = Options, user_ctx = UserCtx,
         type = Type, view = View,
-        start_time = StartTime
+        start_time = StartTime,
+        stats = Stats
     } = Rep,
     % Adjust minimum number of http source connections to 2 to avoid deadlock
     Src = adjust_maxconn(Src0, BaseId),
@@ -631,7 +624,8 @@ init_state(Rep) ->
         checkpoint_interval = get_value(checkpoint_interval, Options,
                                         ?DEFAULT_CHECKPOINT_INTERVAL),
         type = Type,
-        view = View
+        view = View,
+        stats = Stats
     },
     State#rep_state{timer = start_timer(State)}.
 
@@ -983,6 +977,7 @@ update_task(State) ->
         current_through_seq = {_, ThroughSeq},
         highest_seq_done = {_, HighestSeq}
     } = State,
+    update_scheduler_job_stats(State),
     couch_task_status:update(
         rep_stats(State) ++ [
         {source_seq, HighestSeq},
@@ -990,6 +985,11 @@ update_task(State) ->
     ]).
 
 
+update_scheduler_job_stats(#rep_state{rep_details = Rep, stats = Stats}) ->
+    JobId = Rep#rep.id,
+    couch_replicator_scheduler:update_job_stats(JobId, Stats).
+
+
 rep_stats(State) ->
     #rep_state{
         committed_seq = {_, CommittedSeq},
diff --git a/src/couch_replicator/test/couch_replicator_retain_stats_between_job_runs.erl b/src/couch_replicator/test/couch_replicator_retain_stats_between_job_runs.erl
new file mode 100644
index 000000000..3b7377b78
--- /dev/null
+++ b/src/couch_replicator/test/couch_replicator_retain_stats_between_job_runs.erl
@@ -0,0 +1,160 @@
+% Licensed under the Apache License, Version 2.0 (the "License"); you may not
+% use this file except in compliance with the License. You may obtain a copy of
+% the License at
+%
+%   http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+% License for the specific language governing permissions and limitations under
+% the License.
+
+-module(couch_replicator_retain_stats_between_job_runs).
+
+-include_lib("couch/include/couch_eunit.hrl").
+-include_lib("couch/include/couch_db.hrl").
+-include_lib("couch_replicator/src/couch_replicator.hrl").
+
+-define(DELAY, 500).
+-define(TIMEOUT, 60000).
+-define(i2l(I), integer_to_list(I)).
+-define(io2b(Io), iolist_to_binary(Io)).
+
+
+setup() ->
+    Ctx = test_util:start_couch([couch_replicator]),
+    Source = setup_db(),
+    Target = setup_db(),
+    {Ctx, {Source, Target}}.
+
+
+teardown({Ctx, {Source, Target}}) ->
+    teardown_db(Source),
+    teardown_db(Target),
+    ok = application:stop(couch_replicator),
+    ok = test_util:stop_couch(Ctx).
+
+
+stats_retained_test_() ->
+    {
+        setup,
+        fun setup/0,
+        fun teardown/1,
+        fun t_stats_retained/1
+    }.
+
+
+t_stats_retained({_Ctx, {Source, Target}}) ->
+    ?_test(begin
+        populate_db(Source, 42),
+        {ok, RepPid, RepId} = replicate(Source, Target),
+        wait_target_in_sync(Source, Target),
+        check_active_tasks(42, 42),
+        reschedule_job(RepPid),
+        check_active_tasks(42, 42),
+        couch_replicator_scheduler:remove_job(RepId)
+    end).
+
+
+setup_db() ->
+    DbName = ?tempdb(),
+    {ok, Db} = couch_db:create(DbName, [?ADMIN_CTX]),
+    ok = couch_db:close(Db),
+    DbName.
+
+
+teardown_db(DbName) ->
+    ok = couch_server:delete(DbName, [?ADMIN_CTX]),
+    ok.
+
+
+reschedule_job(RepPid) ->
+    Ref = erlang:monitor(process, RepPid),
+    gen_server:cast(couch_replicator_scheduler, {set_max_jobs, 0}),
+    couch_replicator_scheduler:reschedule(),
+    receive
+        {'DOWN', Ref, _, _, _} -> ok
+    after ?TIMEOUT ->
+        erlang:error(timeout)
+    end,
+    gen_server:cast(couch_replicator_scheduler, {set_max_jobs, 500}),
+    couch_replicator_scheduler:reschedule().
+
+
+check_active_tasks(DocsRead, DocsWritten) ->
+    RepTask = wait_for_task_status(),
+    ?assertNotEqual(timeout, RepTask),
+    ?assertEqual(DocsRead, couch_util:get_value(docs_read, RepTask)),
+    ?assertEqual(DocsWritten, couch_util:get_value(docs_written, RepTask)).
+
+
+replication_tasks() ->
+    lists:filter(fun(P) ->
+        couch_util:get_value(type, P) =:= replication
+    end, couch_task_status:all()).
+
+
+wait_for_task_status() ->
+    test_util:wait(fun() ->
+        case replication_tasks() of
+            [] -> wait;
+            [RepTask] -> RepTask
+        end
+    end).
+
+
+populate_db(DbName, DocCount) ->
+    {ok, Db} = couch_db:open_int(DbName, []),
+    Docs = lists:foldl(
+        fun(DocIdCounter, Acc) ->
+            Id = ?io2b(["doc", ?i2l(DocIdCounter)]),
+            Doc = #doc{id = Id, body = {[]}},
+            [Doc | Acc]
+        end,
+        [], lists:seq(1, DocCount)),
+    {ok, _} = couch_db:update_docs(Db, Docs, []),
+    ok = couch_db:close(Db).
+
+
+wait_target_in_sync(Source, Target) ->
+    {ok, SourceDb} = couch_db:open_int(Source, []),
+    {ok, SourceInfo} = couch_db:get_db_info(SourceDb),
+    ok = couch_db:close(SourceDb),
+    SourceDocCount = couch_util:get_value(doc_count, SourceInfo),
+    wait_target_in_sync_loop(SourceDocCount, Target, 300).
+
+
+wait_target_in_sync_loop(_DocCount, _TargetName, 0) ->
+    erlang:error({assertion_failed, [
+          {module, ?MODULE}, {line, ?LINE},
+          {reason, "Could not get source and target databases in sync"}
+    ]});
+
+wait_target_in_sync_loop(DocCount, TargetName, RetriesLeft) ->
+    {ok, Target} = couch_db:open_int(TargetName, []),
+    {ok, TargetInfo} = couch_db:get_db_info(Target),
+    ok = couch_db:close(Target),
+    TargetDocCount = couch_util:get_value(doc_count, TargetInfo),
+    case TargetDocCount == DocCount of
+        true ->
+            true;
+        false ->
+            ok = timer:sleep(?DELAY),
+            wait_target_in_sync_loop(DocCount, TargetName, RetriesLeft - 1)
+    end.
+
+
+replicate(Source, Target) ->
+    SrcUrl = couch_replicator_test_helper:db_url(Source),
+    TgtUrl = couch_replicator_test_helper:db_url(Target),
+    RepObject = {[
+        {<<"source">>, SrcUrl},
+        {<<"target">>, TgtUrl},
+        {<<"continuous">>, true}
+    ]},
+    {ok, Rep} = couch_replicator_utils:parse_rep_doc(RepObject, ?ADMIN_USER),
+    ok = couch_replicator_scheduler:add_job(Rep),
+    couch_replicator_scheduler:reschedule(),
+    Pid = couch_replicator_test_helper:get_pid(Rep#rep.id),
+    {ok, Pid, Rep#rep.id}.