There are three different storage engine concurrency adjustment algorithms:

• kFixedConcurrentTransactions → One single ticket pool with server parameter adjustment.
• kFixedConcurrentTransactionsWithPrioritization → Two ticket pools with server parameter adjustment.
• kThroughputProbing → One single ticket pool with server-side adjustments.

And, translated into code, the components that manage the different algorithms are:

• SinglePoolTicketingSystem for kFixedConcurrentTransactions → Acts as fixed concurrency, where only a single read/write ticket pool exists.
• ThroughputProbingTicketingSystem for kThroughputProbing → An extension of SinglePoolTicketingSystem that disallows runtime adjustment via server parameters and enables the throughput probing algorithm.
• MultiplePoolsTicketingSystem for kFixedConcurrentTransactionsWithPrioritization → Provides two read/write ticket pools: one for normal-priority operations and another for low-priority operations. This configuration is intended to be used together with mongotune.