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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5544) Implement Internal Timer Service in RocksDB
Date Wed, 29 Nov 2017 09:03:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5544?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16270433#comment-16270433

ASF GitHub Bot commented on FLINK-5544:

Github user StefanRRichter commented on the issue:

    I think this implementation was (close to complete) and should be working, but the PR
is outdated. I think it should be possible to attempt a manual rebase.

> Implement Internal Timer Service in RocksDB
> -------------------------------------------
>                 Key: FLINK-5544
>                 URL: https://issues.apache.org/jira/browse/FLINK-5544
>             Project: Flink
>          Issue Type: New Feature
>          Components: State Backends, Checkpointing
>            Reporter: Xiaogang Shi
>            Assignee: Xiaogang Shi
> Now the only implementation of internal timer service is HeapInternalTimerService which
stores all timers in memory. In the cases where the number of keys is very large, the timer
service will cost too much memory. A implementation which stores timers in RocksDB seems good
to deal with these cases.
> It might be a little challenging to implement a RocksDB timer service because the timers
are accessed in different ways. When timers are triggered, we need to access timers in the
order of timestamp. But when performing checkpoints, we must have a method to obtain all timers
of a given key group.
> A good implementation, as suggested by [~StephanEwen], follows the idea of merge sorting.
We can store timers in RocksDB with the format {{KEY_GROUP#TIMER#KEY}}. In this way, the timers
under a key group are put together and are sorted. 
> Then we can deploy an in-memory heap which keeps the first timer of each key group to
get the next timer to trigger. When a key group's first timer is updated, we can efficiently
update the heap.

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