Add a proper reshard jobs ioq class

This lets users bypass it just like any other ioq classes.

Improving on https://github.com/apache/couchdb/pull/4267

4 files changed, 12 insertions, 3 deletions

diff --git a/src/docs/src/config/ioq.rst b/src/docs/src/config/ioq.rst
index ef931b383..f96022590 100644
--- a/src/docs/src/config/ioq.rst
+++ b/src/docs/src/config/ioq.rst
@@ -75,6 +75,10 @@ according to the settings described below.
 
         Disk IO issued by compaction jobs.
 
+    .. config:option:: reshard :: Bypass Disk IO for resharding jobs
+
+        Disk IO issued by resharding jobs.
+
     Without any configuration CouchDB will enqueue all classes of IO. The
     default.ini configuration file that ships with CouchDB activates a bypass
     for each of the interactive IO classes and only background IO goes into the
@@ -87,6 +91,7 @@ according to the settings described below.
         view_update = true
         shard_sync = false
         compaction = false
+        reshard = false
 
 Recommendations
 ===============
diff --git a/src/ioq/src/ioq.erl b/src/ioq/src/ioq.erl
index 038d63bae..f5d3a0491 100644
--- a/src/ioq/src/ioq.erl
+++ b/src/ioq/src/ioq.erl
@@ -76,6 +76,7 @@ bypass(Priority) ->
         read -> config:get_boolean("ioq.bypass", "read", true);
         write -> config:get_boolean("ioq.bypass", "write", true);
         view_update -> config:get_boolean("ioq.bypass", "view_update", true);
+        reshard -> config:get_boolean("ioq.bypass", "reshard", false);
         shard_sync -> config:get_boolean("ioq.bypass", "shard_sync", false);
         compaction -> config:get_boolean("ioq.bypass", "compaction", false);
         _ -> config:get("ioq.bypass", atom_to_list(Priority)) =:= "true"
@@ -103,6 +104,8 @@ io_class(_, {search, _}) ->
     search;
 io_class(_, {search, _, _}) ->
     search;
+io_class(_, {reshard, _}) ->
+    reshard;
 io_class(_, _) ->
     other.
 
@@ -182,6 +185,8 @@ enqueue_request(#request{priority = compaction} = Request, #state{} = State) ->
     State#state{background = queue:in(Request, State#state.background)};
 enqueue_request(#request{priority = shard_sync} = Request, #state{} = State) ->
     State#state{background = queue:in(Request, State#state.background)};
+enqueue_request(#request{priority = reshard} = Request, #state{} = State) ->
+    State#state{background = queue:in(Request, State#state.background)};
 enqueue_request(#request{} = Request, #state{} = State) ->
     State#state{interactive = queue:in(Request, State#state.interactive)}.
 
diff --git a/src/mem3/src/mem3_reshard_index.erl b/src/mem3/src/mem3_reshard_index.erl
index 54cb08ebe..d45701362 100644
--- a/src/mem3/src/mem3_reshard_index.erl
+++ b/src/mem3/src/mem3_reshard_index.erl
@@ -104,8 +104,7 @@ hastings_indices(DbName, Doc) ->
     end.
 
 build_index({?MRVIEW, DbName, MRSt} = Ctx, Try) ->
-    IdxName = couch_mrview_index:get(idx_name, MRSt),
-    ioq:set_io_priority({view_compact, DbName, IdxName}),
+    ioq:set_io_priority({reshard, DbName}),
     await_retry(
         couch_index_server:get_index(couch_mrview_index, MRSt),
         fun couch_index:get_state/2,
diff --git a/src/mem3/src/mem3_reshard_job.erl b/src/mem3/src/mem3_reshard_job.erl
index 1be74dfba..25ff1cf19 100644
--- a/src/mem3/src/mem3_reshard_job.erl
+++ b/src/mem3/src/mem3_reshard_job.erl
@@ -367,7 +367,7 @@ initial_copy_impl(#job{source = Source, target = Targets0} = Job) ->
     #shard{name = SourceName} = Source,
     Targets = [{R, N} || #shard{range = R, name = N} <- Targets0],
     TMap = maps:from_list(Targets),
-    ioq:set_io_priority({db_compact, SourceName}),
+    ioq:set_io_priority({reshard, SourceName}),
     LogMsg1 = "~p initial_copy started ~s",
     LogArgs1 = [?MODULE, shardsstr(Source, Targets0)],
     couch_log:notice(LogMsg1, LogArgs1),