ZKDatabase.committedLog retains the past 500 transactions to enable fast catch-up. This works great, but it's using triple the memory it needs to by retaining three copies of the data part of any transaction.
- The first is in committedLog[i].request.request.hb - a heap-allocated ByteBuffer.
- The second is in committedLog[i].request.txn.data - a jute-serialised record of the transaction
- The third is in committedLog[i].packet.data - also jute-serialised, seemingly uninitialised data.
This means that a ZK-server could be using 1G of memory more than it should be in the worst case. We should use just one copy of the data, even if we really have to refer to it 3 times.