eiri commented on a change in pull request #496: Couchdb 3287 pluggable storage
engines
URL: https://github.com/apache/couchdb/pull/496#discussion_r117531210
##########
File path: src/couch/src/couch_server.erl
##########
@@ -559,6 +591,110 @@ db_closed(Server, Options) ->
true -> Server
end.
+
+get_configured_engines() ->
+ ConfigEntries = config:get("couchdb_engines"),
+ Engines = lists:flatmap(fun({Extension, ModuleStr}) ->
+ try
+ [{Extension, list_to_atom(ModuleStr)}]
+ catch _T:_R ->
+ []
+ end
+ end, ConfigEntries),
+ case Engines of
+ [] ->
+ [{"couch", couch_bt_engine}];
+ Else ->
+ Else
+ end.
+
+
+get_engine(Server, DbName, Options) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ case couch_util:get_value(engine, Options) of
+ Ext when is_binary(Ext) ->
+ ExtStr = binary_to_list(Ext),
+ case couch_util:get_value(ExtStr, Engines) of
+ Engine when is_atom(Engine) ->
+ Path = make_filepath(RootDir, DbName, ExtStr),
+ {Engine, Path};
+ _ ->
+ get_engine(Server, DbName)
+ end;
+ _ ->
+ get_engine(Server, DbName)
+ end.
+
+
+get_engine(Server, DbName) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ Possible = get_possible_engines(DbName, RootDir, Engines),
+ case Possible of
+ [] ->
+ get_default_engine(Server, DbName);
+ [Engine] ->
+ Engine;
+ _ ->
+ erlang:error(engine_conflict)
+ end.
+
+
+get_possible_engines(DbName, RootDir, Engines) ->
+ lists:foldl(fun({Extension, Engine}, Acc) ->
+ Path = make_filepath(RootDir, DbName, Extension),
+ case couch_db_engine:exists(Engine, Path) of
+ true ->
+ [{Engine, Path} | Acc];
+ false ->
+ Acc
+ end
+ end, [], Engines).
+
+
+get_default_engine(Server, DbName) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ Default = {couch_bt_engine, make_filepath(RootDir, DbName, "couch")},
+ case config:get("couchdb", "default_engine") of
Review comment:
@tonysun83 So I've made the same mistake you did and it took me some time to
figure it out. An engine name in "default_engine" is not a name of a module,
but one of "couchdb_engines" section key aka db file's extension. In your case
you are setting default engine to "couch_ngen", but it should be "ngen".
To be fair @garrensmith did the same mistake in his otherwise very helping
setup instruction and set default engine to "couch_bt_engine", which worked
only because it _is_ default in case of misconfiguration.
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