RFC: multi-generation log cache

[killme2008]

RFC: multi-generation log cache

As discussion in #840 , jraft keeps a cache for latest log entries, it's unlimited and may consume too much memory under write-heavy workload or catching up replication when node restarts.

I think we can abstracts a cache interface and provide a multi-generation cache to replace current one:

• Gen-1: totaly in memory with limited capacity.
• Gen-2: Off-heap cache.When Gen-1 overflows, move the LRU(least recently used) item into off-heap cache such as OHC.

Main goals:

• Abstracts log cache interface.
• Provide a multi-generation cache implementation.

[HHoflittlefish777]

@killme2008 hi，I have some Off-heap cache experience before ，and I accept issue #856 ，but the programme wait to discuss,so I want to do this first,and I have time do them together，can you assign me?

[killme2008]

@HHoflittlefish777 Of course, it's yours, feel free to try and discuss with us in slack.

[HHoflittlefish777]

@HHoflittlefish777 Of course, it's yours, feel free to try and discuss with us in slack.

Thanks ,I will discuss in slack later

[HHoflittlefish777]

@killme2008 Hi，I ask some question in slack yesterday,hope to be given a answer if have time.

[killme2008]

@HHoflittlefish777 do not have time to impl this feature, it's open for any developers that are interested in it.

[RockRockWhite]

@killme2008 @hzh0425 Hello, I'm learning MIT 6.824 Course now, and I've passed the Lab2 in which I implemented Raft. I am not so familiar with JVM. But whatever, I want to have a try. Can you assign me?

[hzh0425]

@killme2008 @hzh0425 Hello, I'm learning MIT 6.824 Course now, and I've passed the Lab2 in which I implemented Raft. I am not so familiar with JVM. But whatever, I want to have a try. Can you assign me?

Sure, already assigned to you @RockRockWhite

[hzh0425]

@RockRockWhite You can submit a RFC first

[shihuili1218]

@RockRockWhite May I ask this task is still being implemented?