Ensure io_priority is explicitly set throughout CouchDB

22 files changed, 94 insertions, 5 deletions

diff --git a/src/chttpd/src/chttpd_auth_cache.erl b/src/chttpd/src/chttpd_auth_cache.erl
index 638d8c748..17e448f51 100644
--- a/src/chttpd/src/chttpd_auth_cache.erl
+++ b/src/chttpd/src/chttpd_auth_cache.erl
@@ -139,7 +139,9 @@ spawn_changes(Since) ->
     Pid.
 
 listen_for_changes(Since) ->
-    ensure_auth_ddoc_exists(dbname(), <<"_design/_auth">>),
+    DbName = dbname(),
+    erlang:put(io_priority, {system, DbName}),
+    ensure_auth_ddoc_exists(DbName, <<"_design/_auth">>),
     CBFun = fun ?MODULE:changes_callback/2,
     Args = #changes_args{
         feed = "continuous",
@@ -147,7 +149,7 @@ listen_for_changes(Since) ->
         heartbeat = true,
         filter = {default, main_only}
     },
-    fabric:changes(dbname(), CBFun, Since, Args).
+    fabric:changes(DbName, CBFun, Since, Args).
 
 changes_callback(waiting_for_updates, Acc) ->
     {ok, Acc};
diff --git a/src/couch/src/couch_auth_cache.erl b/src/couch/src/couch_auth_cache.erl
index 157b0902e..3f40bab11 100644
--- a/src/couch/src/couch_auth_cache.erl
+++ b/src/couch/src/couch_auth_cache.erl
@@ -150,6 +150,7 @@ init(_) ->
     ?BY_USER = ets:new(?BY_USER, [set, protected, named_table]),
     ?BY_ATIME = ets:new(?BY_ATIME, [ordered_set, private, named_table]),
     AuthDbName = config:get("couch_httpd_auth", "authentication_db"),
+    erlang:put(io_priority, {system, AuthDbName}),
     process_flag(trap_exit, true),
     ok = config:listen_for_changes(?MODULE, nil),
     {ok, Listener} = couch_event:link_listener(
diff --git a/src/couch/src/couch_doc.erl b/src/couch/src/couch_doc.erl
index 4a49372c7..17d559708 100644
--- a/src/couch/src/couch_doc.erl
+++ b/src/couch/src/couch_doc.erl
@@ -433,6 +433,13 @@ len_doc_to_multi_part_stream(Boundary, JsonBytes, Atts, SendEncodedAtts) ->
 
 doc_to_multi_part_stream(Boundary, JsonBytes, Atts, WriteFun,
     SendEncodedAtts) ->
+    case erlang:get(io_priority) of
+        undefined ->
+            %% TODO: use proper dbname here
+            erlang:put(interactive, <<"asdf">>);
+        _ ->
+            ok
+    end,
     AttsToInclude = lists:filter(fun(Att)-> couch_att:fetch(data, Att) /= stub end, Atts),
     AttsDecoded = decode_attributes(AttsToInclude, SendEncodedAtts),
     AttFun = case SendEncodedAtts of
diff --git a/src/couch/src/couch_httpd.erl b/src/couch/src/couch_httpd.erl
index 3cdfc0ca3..eea98d533 100644
--- a/src/couch/src/couch_httpd.erl
+++ b/src/couch/src/couch_httpd.erl
@@ -229,6 +229,8 @@ handle_request(MochiReq, DefaultFun, UrlHandlers, DbUrlHandlers,
 
 handle_request_int(MochiReq, DefaultFun,
             UrlHandlers, DbUrlHandlers, DesignUrlHandlers) ->
+    %% TODO: find appropriate value for internal API
+    erlang:put(io_priority, {interactive, <<"asdf">>}),
     Begin = os:timestamp(),
     % for the path, use the raw path with the query string and fragment
     % removed, but URL quoting left intact
diff --git a/src/couch/src/couch_httpd_db.erl b/src/couch/src/couch_httpd_db.erl
index 6cfae9610..2dd2b107d 100644
--- a/src/couch/src/couch_httpd_db.erl
+++ b/src/couch/src/couch_httpd_db.erl
@@ -39,6 +39,8 @@
 % Database request handlers
 handle_request(#httpd{path_parts=[DbName|RestParts],method=Method,
         db_url_handlers=DbUrlHandlers}=Req)->
+    %% TODO: set proper io_priority value here
+    erlang:put(io_priority, {interactive, DbName}),
     case {Method, RestParts} of
     {'PUT', []} ->
         create_db_req(Req, DbName);
diff --git a/src/couch/src/couch_httpd_multipart.erl b/src/couch/src/couch_httpd_multipart.erl
index 33795a3a1..b2e1851ca 100644
--- a/src/couch/src/couch_httpd_multipart.erl
+++ b/src/couch/src/couch_httpd_multipart.erl
@@ -26,7 +26,9 @@
 decode_multipart_stream(ContentType, DataFun, Ref) ->
     Parent = self(),
     NumMpWriters = num_mp_writers(),
+    Priority = erlang:get(io_priority),
     {Parser, ParserRef} = spawn_monitor(fun() ->
+        erlang:put(io_priority, Priority),
         ParentRef = erlang:monitor(process, Parent),
         put(mp_parent_ref, ParentRef),
         num_mp_writers(NumMpWriters),
@@ -244,6 +246,14 @@ atts_to_mp([], _Boundary, WriteFun, _AttFun) ->
     WriteFun(<<"--">>);
 atts_to_mp([{Att, Name, Len, Type, Encoding} | RestAtts], Boundary, WriteFun,
     AttFun)  ->
+    case erlang:get(io_priority) of
+        undefined ->
+            %% TODO: set proper io_priority
+            %% TODO: this case shouldn't happen
+            erlang:put(io_priority, {interactive, <<"asdf">>});
+        _ ->
+            ok
+    end,
     LengthBin = list_to_binary(integer_to_list(Len)),
     % write headers
     WriteFun(<<"\r\nContent-Disposition: attachment; filename=\"", Name/binary, "\"">>),
diff --git a/src/couch/src/couch_multidb_changes.erl b/src/couch/src/couch_multidb_changes.erl
index b6a7873fb..95e0776bb 100644
--- a/src/couch/src/couch_multidb_changes.erl
+++ b/src/couch/src/couch_multidb_changes.erl
@@ -231,6 +231,7 @@ start_changes_reader(DbName, Since) ->
 
 
 changes_reader(Server, DbName, Since) ->
+    erlang:put(io_priority, {system, DbName}),
     {ok, Db} = couch_db:open_int(DbName, [?CTX, sys_db]),
     ChangesArgs = #changes_args{
         include_docs = true,
@@ -253,9 +254,10 @@ changes_reader_cb(_, _, Acc) ->
 
 
 scan_all_dbs(Server, DbSuffix) when is_pid(Server) ->
+    DbName = config:get("mem3", "shards_db", "_dbs"),
+    erlang:put(io_priority, {system, DbName}),
     ok = scan_local_db(Server, DbSuffix),
-    {ok, Db} = mem3_util:ensure_exists(
-        config:get("mem3", "shards_db", "_dbs")),
+    {ok, Db} = mem3_util:ensure_exists(DbName),
     ChangesFun = couch_changes:handle_changes(#changes_args{}, nil, Db, nil),
     ChangesFun({fun scan_changes_cb/3, {Server, DbSuffix, 1}}),
     couch_db:close(Db).
diff --git a/src/couch_index/src/couch_index.erl b/src/couch_index/src/couch_index.erl
index cae95779e..b593e4971 100644
--- a/src/couch_index/src/couch_index.erl
+++ b/src/couch_index/src/couch_index.erl
@@ -81,6 +81,7 @@ get_compactor_pid(Pid) ->
 
 init({Mod, IdxState}) ->
     DbName = Mod:get(db_name, IdxState),
+    erlang:put(io_priority, {system, DbName}),
     erlang:send_after(?CHECK_INTERVAL, self(), maybe_close),
     Resp = couch_util:with_db(DbName, fun(Db) ->
         case Mod:open(Db, IdxState) of
diff --git a/src/couch_index/src/couch_index_compactor.erl b/src/couch_index/src/couch_index_compactor.erl
index 61f406c1a..8849cf67d 100644
--- a/src/couch_index/src/couch_index_compactor.erl
+++ b/src/couch_index/src/couch_index_compactor.erl
@@ -117,6 +117,8 @@ compact(Parent, Mod, IdxState) ->
 
 compact(Idx, Mod, IdxState, Opts) ->
     DbName = Mod:get(db_name, IdxState),
+    IndexName = Mod:get(idx_name, IdxState),
+    erlang:put(io_priority, {view_compact, DbName, IndexName}),
     Args = [DbName, Mod:get(idx_name, IdxState)],
     couch_log:info("Compaction started for db: ~s idx: ~s", Args),
     {ok, NewIdxState} = couch_util:with_db(DbName, fun(Db) ->
diff --git a/src/couch_index/src/couch_index_updater.erl b/src/couch_index/src/couch_index_updater.erl
index 7864bde4d..fb15db052 100644
--- a/src/couch_index/src/couch_index_updater.erl
+++ b/src/couch_index/src/couch_index_updater.erl
@@ -128,6 +128,8 @@ code_change(_OldVsn, State, _Extra) ->
 
 update(Idx, Mod, IdxState) ->
     DbName = Mod:get(db_name, IdxState),
+    IndexName = Mod:get(idx_name, IdxState),
+    erlang:put(io_priority, {view_update, DbName, IndexName}),
     CurrSeq = Mod:get(update_seq, IdxState),
     UpdateOpts = Mod:get(update_options, IdxState),
     CommittedOnly = lists:member(committed_only, UpdateOpts),
diff --git a/src/couch_mrview/src/couch_mrview_updater.erl b/src/couch_mrview/src/couch_mrview_updater.erl
index dcc70e4c2..82d1f6599 100644
--- a/src/couch_mrview/src/couch_mrview_updater.erl
+++ b/src/couch_mrview/src/couch_mrview_updater.erl
@@ -225,6 +225,7 @@ map_docs(Parent, #mrst{db_name = DbName, idx_name = IdxName} = State0) ->
 
 
 write_results(Parent, #mrst{db_name = DbName, idx_name = IdxName} = State) ->
+    erlang:put(io_priority, {view_update, DbName, IdxName}),
     case accumulate_writes(State, State#mrst.write_queue, nil) of
         stop ->
             Parent ! {new_state, State};
diff --git a/src/couch_peruser/src/couch_peruser.erl b/src/couch_peruser/src/couch_peruser.erl
index 886fb4f6e..08fc3d7a0 100644
--- a/src/couch_peruser/src/couch_peruser.erl
+++ b/src/couch_peruser/src/couch_peruser.erl
@@ -73,6 +73,7 @@ init_state() ->
         couch_log:debug("peruser: enabled on node ~p", [node()]),
         DbName = ?l2b(config:get(
                          "couch_httpd_auth", "authentication_db", "_users")),
+        erlang:put(io_priority, {system, DbName}),
         DeleteDbs = config:get_boolean("couch_peruser", "delete_dbs", false),
         Q = config:get_integer("couch_peruser", "q", 1),
         Prefix = config:get("couch_peruser", "database_prefix", ?DEFAULT_USERDB_PREFIX),
@@ -137,6 +138,7 @@ start_listening(#state{db_name=DbName, delete_dbs=DeleteDbs,
 
 -spec init_changes_handler(ChangesState :: #changes_state{}) -> ok.
 init_changes_handler(#changes_state{db_name=DbName} = ChangesState) ->
+    erlang:put(io_priority, {system, DbName}),
     % couch_log:debug("peruser: init_changes_handler() on DbName ~p", [DbName]),
     try
         {ok, Db} = couch_db:open_int(DbName, [?ADMIN_CTX, sys_db]),
diff --git a/src/couch_replicator/src/couch_replicator_api_wrap.erl b/src/couch_replicator/src/couch_replicator_api_wrap.erl
index 44c290d33..825b70678 100644
--- a/src/couch_replicator/src/couch_replicator_api_wrap.erl
+++ b/src/couch_replicator/src/couch_replicator_api_wrap.erl
@@ -216,6 +216,10 @@ ensure_full_commit(Db) ->
 
 
 get_missing_revs(#httpdb{} = Db, IdRevs) ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, db_uri(Db)});
+        _ -> ok
+    end,
     JsonBody = {[{Id, couch_doc:revs_to_strs(Revs)} || {Id, Revs} <- IdRevs]},
     send_req(
         Db,
@@ -234,6 +238,10 @@ get_missing_revs(#httpdb{} = Db, IdRevs) ->
             {ok, lists:map(ConvertToNativeFun, Props)}
         end);
 get_missing_revs(Db, IdRevs) ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, couch_db:name(Db)});
+        _ -> ok
+    end,
     couch_db:get_missing_revs(Db, IdRevs).
 
 
@@ -250,6 +258,7 @@ open_doc_revs(#httpdb{} = HttpDb, Id, Revs, Options, Fun, Acc) ->
     Path = encode_doc_id(Id),
     QS = options_to_query_args(HttpDb, Path, [revs, {open_revs, Revs} | Options]),
     {Pid, Ref} = spawn_monitor(fun() ->
+        erlang:put(io_priority, {system, db_uri(HttpDb)}),
         Self = self(),
         Callback = fun
           (200, Headers, StreamDataFun) ->
@@ -753,6 +762,8 @@ receive_docs(Streamer, UserFun, Ref, UserAcc) ->
 
 run_user_fun(UserFun, Arg, UserAcc, OldRef) ->
     {Pid, Ref} = spawn_monitor(fun() ->
+        %% TODO: find proper db name value here
+        erlang:put(io_priority, {system, <<"asdf">>}),
         try UserFun(Arg, UserAcc) of
             Resp ->
                 exit({exit_ok, Resp})
diff --git a/src/couch_replicator/src/couch_replicator_changes_reader.erl b/src/couch_replicator/src/couch_replicator_changes_reader.erl
index 2e4df5365..c0f2d7171 100644
--- a/src/couch_replicator/src/couch_replicator_changes_reader.erl
+++ b/src/couch_replicator/src/couch_replicator_changes_reader.erl
@@ -37,6 +37,7 @@ start_link(StartSeq, #httpdb{} = Db, ChangesQueue, Options) ->
 start_link(StartSeq, Db, ChangesQueue, Options) ->
     Parent = self(),
     {ok, spawn_link(fun() ->
+        erlang:put(io_priority, {interactive, couch_db:name(Db)}),
         ?MODULE:read_changes(Parent, StartSeq, Db, ChangesQueue, Options)
     end)}.
 
diff --git a/src/couch_replicator/src/couch_replicator_docs.erl b/src/couch_replicator/src/couch_replicator_docs.erl
index bbf9694d7..178586198 100644
--- a/src/couch_replicator/src/couch_replicator_docs.erl
+++ b/src/couch_replicator/src/couch_replicator_docs.erl
@@ -123,6 +123,10 @@ update_error(#rep{db_name = DbName, doc_id = DocId, id = RepId}, Error) ->
 
 -spec ensure_rep_db_exists() -> {ok, Db::any()}.
 ensure_rep_db_exists() ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, ?REP_DB_NAME});
+        _ -> ok
+    end,
     Db = case couch_db:open_int(?REP_DB_NAME, [?CTX, sys_db,
             nologifmissing]) of
         {ok, Db0} ->
@@ -137,6 +141,10 @@ ensure_rep_db_exists() ->
 
 -spec ensure_rep_ddoc_exists(binary()) -> ok.
 ensure_rep_ddoc_exists(RepDb) ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, ?REP_DB_NAME});
+        _ -> ok
+    end,
     case mem3:belongs(RepDb, ?REP_DESIGN_DOC) of
         true ->
             ensure_rep_ddoc_exists(RepDb, ?REP_DESIGN_DOC);
@@ -147,6 +155,10 @@ ensure_rep_ddoc_exists(RepDb) ->
 
 -spec ensure_rep_ddoc_exists(binary(), binary()) -> ok.
 ensure_rep_ddoc_exists(RepDb, DDocId) ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, ?REP_DB_NAME});
+        _ -> ok
+    end,
     case open_rep_doc(RepDb, DDocId) of
         {not_found, no_db_file} ->
             %% database was deleted.
diff --git a/src/couch_replicator/src/couch_replicator_filters.erl b/src/couch_replicator/src/couch_replicator_filters.erl
index 5668820d1..b8bec56cb 100644
--- a/src/couch_replicator/src/couch_replicator_filters.erl
+++ b/src/couch_replicator/src/couch_replicator_filters.erl
@@ -66,7 +66,9 @@ parse(Options) ->
 -spec fetch(binary(), binary(), binary(), #user_ctx{}) ->
     {ok, {[_]}} | {error, binary()}.
 fetch(DDocName, FilterName, Source, UserCtx) ->
+    Priority = erlang:get(io_priority),
     {Pid, Ref} = spawn_monitor(fun() ->
+        erlang:put(io_priority, Priority),
         try fetch_internal(DDocName, FilterName, Source, UserCtx) of
             Resp ->
                 exit({exit_ok, Resp})
diff --git a/src/couch_replicator/src/couch_replicator_scheduler_job.erl b/src/couch_replicator/src/couch_replicator_scheduler_job.erl
index 412ff7d05..a05f80064 100644
--- a/src/couch_replicator/src/couch_replicator_scheduler_job.erl
+++ b/src/couch_replicator/src/couch_replicator_scheduler_job.erl
@@ -109,6 +109,9 @@ init(InitArgs) ->
 
 do_init(#rep{options = Options, id = {BaseId, Ext}, user_ctx=UserCtx} = Rep) ->
     process_flag(trap_exit, true),
+    %% TODO: what value to put here
+    %% what is using this?
+    erlang:put(io_priority, {db_update, <<"asdf">>}),
 
     timer:sleep(startup_jitter()),
 
diff --git a/src/couch_replicator/src/couch_replicator_worker.erl b/src/couch_replicator/src/couch_replicator_worker.erl
index ec98fa0f3..8425ae9b9 100644
--- a/src/couch_replicator/src/couch_replicator_worker.erl
+++ b/src/couch_replicator/src/couch_replicator_worker.erl
@@ -76,6 +76,7 @@ start_link(Cp, #httpdb{} = Source, Target, ChangesManager, MaxConns) ->
 start_link(Cp, Source, Target, ChangesManager, _MaxConns) ->
     Pid = spawn_link(fun() ->
         erlang:put(last_stats_report, os:timestamp()),
+        erlang:put(io_priority, {interactive, couch_db:name(Source)}),
         queue_fetch_loop(Source, Target, Cp, Cp, ChangesManager)
     end),
     {ok, Pid}.
@@ -84,7 +85,11 @@ start_link(Cp, Source, Target, ChangesManager, _MaxConns) ->
 init({Cp, Source, Target, ChangesManager, MaxConns}) ->
     process_flag(trap_exit, true),
     Parent = self(),
+    %% TODO: set proper dbname value here, extract from #httpdb{}/#db{}
+    Priority = {interactive, <<"asdf">>},
+    erlang:put(io_priority, Priority),
     LoopPid = spawn_link(fun() ->
+        erlang:put(io_priority, Priority),
         queue_fetch_loop(Source, Target, Parent, Cp, ChangesManager)
     end),
     erlang:put(last_stats_report, os:timestamp()),
@@ -408,8 +413,10 @@ spawn_writer(Target, #batch{docs = DocList, size = Size}) ->
         ok
     end,
     Parent = self(),
+    Priority = erlang:get(io_priority),
     spawn_link(
         fun() ->
+            erlang:put(io_priority, Priority),
             Target2 = open_db(Target),
             Stats = flush_docs(Target2, DocList),
             close_db(Target2),
diff --git a/src/global_changes/src/global_changes_server.erl b/src/global_changes/src/global_changes_server.erl
index 7e3062586..5f66237da 100644
--- a/src/global_changes/src/global_changes_server.erl
+++ b/src/global_changes/src/global_changes_server.erl
@@ -60,6 +60,9 @@ init([]) ->
     UpdateDb = case UpdateDb0 of "false" -> false; _ -> true end,
     MaxWriteDelay = list_to_integer(MaxWriteDelay0),
 
+    GlobalChangesDbName = global_changes_util:get_dbname(),
+    erlang:put(io_priority, {db_update, GlobalChangesDbName}),
+
     % Start our write triggers
     erlang:send_after(MaxWriteDelay, self(), flush_updates),
 
@@ -68,7 +71,7 @@ init([]) ->
         pending_update_count=0,
         pending_updates=sets:new(),
         max_write_delay=MaxWriteDelay,
-        dbname=global_changes_util:get_dbname(),
+        dbname=GlobalChangesDbName,
         handler_ref=erlang:monitor(process, Handler)
     },
     {ok, State}.
diff --git a/src/mem3/src/mem3_nodes.erl b/src/mem3/src/mem3_nodes.erl
index dd5be1a72..8fbe7c65e 100644
--- a/src/mem3/src/mem3_nodes.erl
+++ b/src/mem3/src/mem3_nodes.erl
@@ -41,6 +41,8 @@ get_node_info(Node, Key) ->
     end.
 
 init([]) ->
+    DbName = list_to_binary(config:get("mem3", "nodes_db", "_nodes")),
+    erlang:put(io_priority, {system, DbName}),
     ets:new(?MODULE, [named_table, {read_concurrency, true}]),
     UpdateSeq = initialize_nodelist(),
     {Pid, _} = spawn_monitor(fun() -> listen_for_changes(UpdateSeq) end),
@@ -109,6 +111,7 @@ first_fold(#full_doc_info{id=Id}=DocInfo, Db) ->
 
 listen_for_changes(Since) ->
     DbName = config:get("mem3", "nodes_db", "_nodes"),
+    erlang:put(io_priority, {system, DbName}),
     {ok, Db} = mem3_util:ensure_exists(DbName),
     Args = #changes_args{
         feed = "continuous",
diff --git a/src/mem3/src/mem3_shards.erl b/src/mem3/src/mem3_shards.erl
index 6afc22f57..5e34921f0 100644
--- a/src/mem3/src/mem3_shards.erl
+++ b/src/mem3/src/mem3_shards.erl
@@ -198,6 +198,8 @@ init([]) ->
     ok = config:listen_for_changes(?MODULE, nil),
     SizeList = config:get("mem3", "shard_cache_size", "25000"),
     WriteTimeout = config:get_integer("mem3", "shard_write_timeout", 1000),
+    DbName = config:get("mem3", "shards_db", "_dbs"),
+    erlang:put(io_priority, {system, DbName}),
     UpdateSeq = get_update_seq(),
     {ok, #st{
         max_size = list_to_integer(SizeList),
@@ -319,6 +321,7 @@ get_update_seq() ->
 
 listen_for_changes(Since) ->
     DbName = config:get("mem3", "shards_db", "_dbs"),
+    erlang:put(io_priority, {system, DbName}),
     {ok, Db} = mem3_util:ensure_exists(DbName),
     Args = #changes_args{
         feed = "continuous",
@@ -365,6 +368,10 @@ changes_callback(timeout, _) ->
 load_shards_from_disk(DbName) when is_binary(DbName) ->
     couch_stats:increment_counter([mem3, shard_cache, miss]),
     X = ?l2b(config:get("mem3", "shards_db", "_dbs")),
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, X});
+        _ -> ok
+    end,
     {ok, Db} = mem3_util:ensure_exists(X),
     try
         load_shards_from_db(Db, DbName)
@@ -373,6 +380,10 @@ load_shards_from_disk(DbName) when is_binary(DbName) ->
     end.
 
 load_shards_from_db(ShardDb, DbName) ->
+    case erlang:get(io_priority) of
+        undefined -> erlang:put(io_priority, {system, couch_db:name(ShardDb)});
+        _ -> ok
+    end,
     case couch_db:open_doc(ShardDb, DbName, [ejson_body]) of
     {ok, #doc{body = {Props}}} ->
         Seq = couch_db:get_update_seq(ShardDb),
diff --git a/src/mem3/src/mem3_util.erl b/src/mem3/src/mem3_util.erl
index b44ca2332..44647838d 100644
--- a/src/mem3/src/mem3_util.erl
+++ b/src/mem3/src/mem3_util.erl
@@ -85,6 +85,7 @@ write_db_doc(Doc) ->
     write_db_doc(DbName, Doc, true).
 
 write_db_doc(DbName, #doc{id=Id, body=Body} = Doc, ShouldMutate) ->
+    erlang:put(io_priority, {system, DbName}),
     {ok, Db} = couch_db:open(DbName, [?ADMIN_CTX]),
     try couch_db:open_doc(Db, Id, [ejson_body]) of
     {ok, #doc{body = Body}} ->
@@ -111,6 +112,7 @@ delete_db_doc(DocId) ->
     delete_db_doc(DbName, DocId, true).
 
 delete_db_doc(DbName, DocId, ShouldMutate) ->
+    erlang:put(io_priority, {system, DbName}),
     {ok, Db} = couch_db:open(DbName, [?ADMIN_CTX]),
     {ok, Revs} = couch_db:open_doc_revs(Db, DocId, all, []),
     try [Doc#doc{deleted=true} || {ok, #doc{deleted=false}=Doc} <- Revs] of