question: @ GwtIncompatible ( "java.util.concurrent.ConcurrentHashMap concurrencyLevel" ) public MapMaker concurrencyLevel ( int concurrencyLevel ) { builder . concurrencyLevel ( concurrencyLevel ) ; return this ; }
target:  Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The table is internally partitioned to try to permit the indicated number of concurrent updates without contention.  Because placement in hash tables is essentially random, the actual concurrency will vary. Ideally, you should choose a value to accommodate as many threads as will ever concurrently modify the table. Using a significantly higher value than you need can waste space and time, and a significantly lower value can lead to thread contention. But overestimates and underestimates within an order of magnitude do not usually have much noticeable impact. A value of one is appropriate when it is known that only one thread will modify and all others will only read. Defaults to 16.