nickva commented on code in PR #4201: URL: https://github.com/apache/couchdb/pull/4201#discussion_r998898093
########## src/fabric/src/fabric_open_revs.erl: ########## @@ -0,0 +1,455 @@ +% 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(fabric_open_revs). + +-export([ + go/3 +]). + +-include_lib("mem3/include/mem3.hrl"). +-include_lib("couch/include/couch_db.hrl"). + +-record(req, { + idrevs, + wcnt = 0, + rcnt = 0, + responses = [] +}). + +-record(st, { + r, + args, + reqs, + workers +}). + +go(_DbName, [], _Options) -> + {ok, []}; +go(DbName, IdsRevsOpts, Options) -> + St = init_state(DbName, IdsRevsOpts, Options), + WShards = maps:keys(St#st.workers), + RexiMon = fabric_util:create_monitors(WShards), + try fabric_util:recv(WShards, #shard.ref, fun handle_message/3, St) of + {timeout, #st{workers = #{} = Workers1}} -> + stop_workers(Workers1), + fabric_util:log_timeout(maps:keys(Workers1), "open_revs"), + {error, timeout}; + Else -> + Else + after + rexi_monitor:stop(RexiMon) + end. + +handle_message([_ | _] = Resps, Worker, #st{} = St) -> + #st{workers = Workers, reqs = Reqs, r = R} = St, + {ArgsRefs, Workers1} = maps:take(Worker, Workers), + ArgsResps = lists:zip(ArgsRefs, Resps), + Reqs1 = lists:foldl(fun responses_fold/2, Reqs, ArgsResps), + case not r_met(Reqs1, R) andalso have_viable_workers(Workers1) of + true -> + {ok, St#st{workers = Workers1, reqs = Reqs1}}; + false -> + stop_workers(Workers1), + {stop, finalize(St#st.args, Reqs1)} + end; +handle_message({rexi_DOWN, _, {_, NodeRef}, _}, _Worker, #st{} = St) -> + #st{workers = Workers, reqs = Reqs} = St, + FilterFun = fun(#shard{node = N}) -> N =:= NodeRef end, + DeadKeys = lists:filter(FilterFun, maps:keys(Workers)), + Workers1 = maps:without(DeadKeys, Workers), + DeadWorkers = maps:with(DeadKeys, Workers), + FoldFun = fun(_, ArgRefs, Acc) -> update_wcnt(Acc, ArgRefs, -1) end, + Reqs1 = maps:fold(FoldFun, Reqs, DeadWorkers), + Error = {error, {nodedown, <<"progress not possible">>}}, + handle_error(Error, St#st{workers = Workers1, reqs = Reqs1}); +handle_message({rexi_EXIT, Reason}, Worker, #st{} = St) -> + handle_message(Reason, Worker, St); +handle_message({error, Reason}, Worker, #st{} = St) -> + handle_message(Reason, Worker, St); +handle_message(Reason, Worker, #st{} = St) -> + #st{workers = Workers, reqs = Reqs} = St, + {DeadArgRefs, Workers1} = maps:take(Worker, Workers), + Reqs1 = update_wcnt(Reqs, DeadArgRefs, -1), + handle_error(Reason, St#st{workers = Workers1, reqs = Reqs1}). + +init_state(DbName, IdsRevsOpts, Options) -> + DefaultR = integer_to_list(mem3:quorum(DbName)), + R = list_to_integer(couch_util:get_value(r, Options, DefaultR)), + {ArgRefs, Reqs0} = build_req_map(IdsRevsOpts), + ShardMap = build_worker_map(DbName, Reqs0), + {Workers, Reqs} = spawn_workers(Reqs0, ShardMap, Options), + #st{r = R, args = ArgRefs, reqs = Reqs, workers = Workers}. + +responses_fold({ArgRef, NewResp}, #{} = Reqs) -> + #{ArgRef := Req} = Reqs, + #req{rcnt = R, wcnt = W, responses = Resps} = Req, + % De-duplicate identical results as we go along + Resps1 = lists:umerge(Resps, lists:usort(NewResp)), + % If responses don't match or got a "not found", don't bump rcnt so we can + % wait for more workers. + NewR = + case {is_not_found(NewResp), length(Resps)} of + {true, _} -> R; + {_, 0} -> R + 1; + {_, OldLen} when OldLen == length(Resps1) -> R + 1; Review Comment: I updated this logic a bit to extract the `OldLen` and `NewLen` out of the case statement. It's a tiny bit less efficient but more clear to read. ```erlang case {any_not_found(NewResp), OldLen} of {true, _} -> R; {_, 0} -> R + 1; {_, L} when L == NewLen -> R + 1; {_, L} when L < NewLen -> R end, ``` In this case `{_, 0}` would not be covered by` {_, L} when L == NewLen -> R + 1` as when the first response comes `OldLen =0` but `NewLen` would be 1. So, they are different, however we do want to bump the `R` count because it's the only response we received and don't have a reason to consider that it's a diverging result. As soon as we have more than one response (`OldLen = 1`) then we switch the logic and bump the `R` count only if we start getting the same length, that is we get the same response. If we get different responses (`OldLen < NewLen`) we stop bumping it because we're hoping to get a more worker responses. -- This is an automated message from the Apache Git Service. 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