rnewson commented on a change in pull request #3734:
URL: https://github.com/apache/couchdb/pull/3734#discussion_r704834096
##########
File path: src/fabric/src/fabric_util.erl
##########
@@ -125,15 +128,40 @@ get_shard([#shard{node = Node, name = Name} | Rest],
Opts, Timeout, Factor) ->
throw(Error);
{Ref, Reason} ->
couch_log:debug("Failed to open shard ~p because: ~p", [Name,
Reason]),
- get_shard(Rest, Opts, Timeout, Factor)
+ FmtReason = lists:flatten(io_lib:format("~p", [Reason])),
+ get_shard(Rest, Opts, Timeout, Factor, FmtReason)
after Timeout ->
couch_log:debug("Failed to open shard ~p after: ~p", [Name,
Timeout]),
- get_shard(Rest, Opts, Factor * Timeout, Factor)
+ NextTimeout = min(request_timeout(), Factor * Timeout),
+ FmtReason = lists:flatten(io_lib:format("timeout ~B msec",
[Timeout])),
+ get_shard(Rest, Opts, NextTimeout, Factor, FmtReason)
end
after
rexi_monitor:stop(Mon)
end.
+
+get_db_timeout(N, Factor, MinTimeout, MaxTimeout) ->
+ %
+ % The progression of timeouts forms a geometric series:
+ %
+ % MaxTimeout = T + T*F + T*F^2 + T*F^3 ...
+ %
+ % Where T is the initial timeout and F is the factor. The formula for
+ % the sum is:
+ %
+ % Sum[T * F^I, I <- 0..N] = T * (1 - F^(N + 1)) / (1 - F)
+ %
+ % Then, for a given sum and factor we can calculate the initial timeout T:
+ %
+ % T = Sum / ((1 - F^(N+1)) / (1 - F))
+ %
+ Timeout = MaxTimeout / ((1 - math:pow(Factor, N + 1)) / (1 - Factor)),
Review comment:
we have exponential backoff algorithms elsewhere (and maybe some simple
linear ones too), the proliferation of different timeout algorithms is
confusing.
##########
File path: src/fabric/src/fabric_util.erl
##########
@@ -100,19 +100,22 @@ get_db(DbName) ->
get_db(DbName, []).
get_db(DbName, Options) ->
- {Local, SameZone, DifferentZone} =
mem3:group_by_proximity(mem3:shards(DbName)),
+ LiveShards = mem3:live_shards(DbName, [node() | nodes()]),
Review comment:
this change is unrelated to the PR topic.
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