Large amounts of create and drop collections can cause listDatabases to be slow under WiredTiger

require "mongo"   client1 = Mongo::Client. new ( 'mongodb://127.0.0.1:27017/' ) client2 = Mongo::Client. new ( 'mongodb://127.0.0.1:27017/' ) client3 = Mongo::Client. new ( 'mongodb://127.0.0.1:27017/' ) client4 = Mongo::Client. new ( 'mongodb://127.0.0.1:27017/' )   Mongo::Logger.logger.level = Logger:: WARN   for x in 0 .. 100 thr = Thread . new { # sleep 1 before = Time .now client1.use( "admin" ).command( :listDatabases => 1 ) after= Time .now p "took: " + (after-before).to_s } thr1 = Thread . new { for i in 0 .. 100 name = "abcd" + ((x* 100 )+i).to_s; client2.use(name)[ :foo ].indexes.create_one({ :x => 1 }) client2.use(name)[ :foo ].insert_one({ :x => 1 }) client2.use(name)[ :baz ].indexes.create_one({ :x => 1 }) client2.use(name)[ :bar ].insert_one({ :x => 1 }) end } thr2 = Thread . new { for i in 0 .. 100 name = "abcd" + ((x* 100 )+i).to_s; client3.use(name)[ :bar ].indexes.create_one({ :x => 1 }) client3.use(name)[ :bar ].insert_one({ :x => 1 }) client3.use(name)[ :qux ].indexes.create_one({ :x => 1 }) client3.use(name)[ :qux ].insert_one({ :x => 1 }) end } thr3 = Thread . new { for i in 0 .. 100 name = "abcd" + ((x* 100 )+i).to_s; client4.use(name)[ :alpha ].indexes.create_one({ :x => 1 }) client4.use(name)[ :alpha ].insert_one({ :x => 1 }) client4.use(name)[ :beta ].indexes.create_one({ :x => 1 }) client4.use(name)[ :beta ].insert_one({ :x => 1 }) end } thr1.join thr2.join thr3.join thr4 = Thread . new { for i in 0 .. 100 name = "abcd" + ((x* 100 )+i).to_s; client2.use(name)[ :foo ].drop client3.use(name)[ :baz ].drop client4.use(name)[ :beta ].drop end } thr4.join sleep 20 thr.join() end