Hi everyone,

I'd like to discuss sharing RocksDB memory across slots as proposed in
FLINK-29928 [1].

Since 1.10 / FLINK-7289 [2], it is possible to:
- share these objects among RocksDB instances of the same slot
- bound the total memory usage by all RocksDB instances of a TM

However, the memory is divided between the slots equally (unless using
fine-grained resource control). This is sub-optimal if some slots contain
more memory intensive tasks than the others.
Using fine-grained resource control is also often not an option because the
workload might not be known in advance.

The proposal is to widen the scope of sharing memory to TM, so that it can
be shared across all RocksDB instances of that TM. That would reduce the
overall memory consumption in exchange for resource isolation.

Please see FLINK-29928 [1] for more details.

Looking forward to feedback on that proposal.

[1]
https://issues.apache.org/jira/browse/FLINK-29928
[2]
https://issues.apache.org/jira/browse/FLINK-7289

Regards,
Roman

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