Hi Gyula, It's the backend that decides the data contained in the snapshot. The backend can take a complete snapshot when it finds it cost more to take an incremental snapshot. In such cases, the taken snapshots are self-contained and will not reference any previous deltas. It's true that the growth in the number of deltas will increase the time taken to recover. But the backend can merge the deltas to limit the number of deltas. The methods to merge deltas may vary a lot in different backends. For example, in RocksDBStateBackend, the merging of deltas is already done in RocksDB via compactions. Regards,Xiaogang
------------------------------------------------------------------发件人：Gyula Fóra <gyf...@apache.org>发送时间：2017年2月18日(星期六) 05:37收件人：dev <dev@flink.apache.org>主 题：Re: [DISCUSS] Support Incremental Checkpointing in Flink Hi! This is an awesome proposal, I am looking forward to seeing it in action :) Some things I have been wondering: Which component decides whether the next checkpoint should be a delta or not? I guess the more deltas we take the longer the recovery time will be if there is many overwrites in the database, on the other hand if we rarely overwrite values it might make sense to keep a lot of deltas. Maybe the statebackend should be able to decide this, it might not make sense to preconfigure this to a fix value, but I am not sure. We could for instance use bloom filters to make the decision. If we created deltas with a lot of duplicate keys then the recovery will suffer potentially outweighing the benefits of the incremental checkpoint itself (it might violate some strict SLA on recovery), would it make sense in some cases to do a merge of the deltas in background batch jobs? This would probably make bookkeeping much harder, so just an idea I wanted to throw in there. Otherwise it seems that a lot of thought went into this, and looks very good! Have a nice weekend! Gyula SHI Xiaogang <shixiaoga...@gmail.com> ezt írta (időpont: 2017. febr. 14., K, 4:18): > Hi all, > > > Incremental checkpointing can help a lot in improving the efficiency of > fault tolerance and recovery in Flink. I wrote an initial design of > incremental checkpointing in Flink, and am looking forwards for your > comments. > > > > >https://docs.google.com/document/d/1VvvPp09gGdVb9D2wHx6NX99yQK0jSUMWHQPrQ_mn520/edit?usp=sharing > > > Some more issues, I think, are needed to be discussed in the introduction > of incremental checkpointing. > > > One is the implementation of savepoints. Savepoints are supposed to be full > and independent of backend implementation. Currently, the implementation of > Savepoints and Checkpoints are identical in backends. With the introduction > of incremental checkpointing, I think backends should take different > snapshots for them. > > > Regards, > > Xiaogang >
