[jira] [Commented] (KAFKA-3184) Add Checkpoint for In-memory State Store

["Ted Yu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16300417#comment-16300417 ] 

Ted Yu commented on KAFKA-3184:
-------------------------------

From InMemoryKeyValueStore :
{code}
    public void flush() {
        // do-nothing since it is in-memory
{code}
For this task, I assume in-memory state store needs to implement flush() (and return true in {{ persistent() }}).
If so, we need to decide the format which flush uses.

> Add Checkpoint for In-memory State Store
> ----------------------------------------
>
>                 Key: KAFKA-3184
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3184
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Guozhang Wang
>              Labels: user-experience
>
> Currently Kafka Streams does not make a checkpoint of the persistent state store upon committing, which would be expensive since it is "stopping the world" and write on disks: for example, RocksDB would require you to copy the file directory to make a copy naively. 
> However, for in-memory stores checkpointing maybe doable in an asynchronous manner hence it can be done quickly. And the benefit of having intermediate checkpoint is to avoid restoring from scratch if standby tasks are not present.



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