RocksDB based timers
Even if you set RocksDB as a state backend, Flink timers, registered by the window operator or defined by the user, are stored on-heap by default. You can change this by setting the timer service property to RocksDB to reduce the heap consumption.
Timers can be user-defined or registered by the system for window operators. While heap based timers are very quick, they might require too large container sizes.
By setting the
configuration property to ROCKSDB, Flink stores all timers in the state
backend. This has a severe impact on timer performance, but also greatly reduces the heap