Hi Henry, In addition to Vino’s answer, there are several things to keep in mind about “checkpoints vs savepoints".
Checkpoints are designed mostly for fault tolerance of running Flink job and automatic recovery that is why by default Flink manages their storage itself. Though it is correct that you can configure the checkpoints to be retained (externalised), have control over their storage and resume a failed/canceled job from them. But their format might be optimised for any of new Flink versions and change between them. It means that in general you might not be able to upgrade Flink version or the running job structure using only checkpoints. Moreover, currently, it is not guaranteed that you will be always able to rescale your job from the checkpoint (change parallelism). Although, it is technically possible for Flink 1.6.0 at the moment, even for incremental checkpoints. Savepoints are designed for manual intervention of the user for maintenance operations that is why their storage is under control of the user in the first place. They have more stable internal format which allows manual migration between Flink or job versions and rescaling. Cheers, Andrey > On 24 Aug 2018, at 12:55, vino yang <yanghua1...@gmail.com> wrote: > > Hi Henry, > > A good answer from stackoverflow: > > Apache Flink's Checkpoints and Savepoints are similar in that way they both > are mechanisms for preserving internal state of Flink's applications. > > Checkpoints are taken automatically and are used for automatic restarting job > in case of a failure. > > Savepoints on the other hand are taken manually, are always stored externally > and are used for starting a "new" job with previous internal state in case of > e.g. > > Bug fixing > Flink version upgrade > A/B testing, etc. > Underneath they are in fact the same mechanism/code path with some subtle > nuances. > > About your question: > > 1) No problem, The main purpose of checkpoint itself is to automatically > restart the recovery when the job fails. > 2) You can also use REST client to trigger savepoint. > 3) I don't know, But it seems that their usage scenarios and purposes are > still different. May Till and Chesnay can answer this question. > > Thanks, vino. > > 徐涛 <happydexu...@gmail.com <mailto:happydexu...@gmail.com>> 于2018年8月24日周五 > 下午3:19写道： > Hi All, > I check the documentation of Flink release 1.6, find that I can use > checkpoints to resume the program either. As I encountered some problems when > using savepoints, I have the following questions: > 1. Can I use checkpoints only, but not use savepoints, because it can > also use to resume programs. If I do so, is there any problem? > 2. Checkpoint can be generated automatically, but savepoints seems can > only be generated manually. I have to write a crontab to generate the > savepoint, more than this, my Flink program is run on Yarn, and on the > machines, only the Hadoop and Yarn are installed, so I can not use flink > savepoint command to generate savepoint, and I have no authorization to > install Flink on the machines. > 3. Will checkpoint and savepoint merged in later releases? > Thanks very much. > > Best, > Henry
