RocksDB based timers
Regardless of the state backend configuration, Flink timers are stored on-heap by default.
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