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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9182) async checkpoints for timer service
Date Thu, 10 May 2018 10:27:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16470189#comment-16470189

ASF GitHub Bot commented on FLINK-9182:

Github user makeyang commented on a diff in the pull request:

    --- Diff: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/HeapInternalTimerService.java
    @@ -49,13 +50,13 @@
     	 * Processing time timers that are currently in-flight.
    -	private final Set<InternalTimer<K, N>>[] processingTimeTimersByKeyGroup;
    +	private final Map<String, InternalTimer<K, N>>[] processingTimeTimersByKeyGroup;
    --- End diff --
    I switch from set to map because in deleteProcessingTimeTimer/deleteEventTimeTimer method,
I have to check if contais Timer with currentKey, namespace and time while I don't have version
    If I use Set as interface, then I have to iterator Set to fetch exactly timer object,
which is not convenient as Map

> async checkpoints for timer service
> -----------------------------------
>                 Key: FLINK-9182
>                 URL: https://issues.apache.org/jira/browse/FLINK-9182
>             Project: Flink
>          Issue Type: Improvement
>          Components: State Backends, Checkpointing
>    Affects Versions: 1.5.0, 1.4.2
>            Reporter: makeyang
>            Assignee: makeyang
>            Priority: Minor
>             Fix For: 1.4.3, 1.5.1
> # problem description:
>  ## with the increase in the number of  'InternalTimer' object the checkpoint more and
more slowly
>  # improvement desgin
>  ## maintain a stateTableVersion, which is exactly the same thing as CopyOnWriteStateTable
and snapshotVersions which is exactly the same thing as CopyOnWriteStateTable in InternalTimeServiceManager.
one more thing: a readwrite lock, which is used to protect snapshotVersions and stateTableVersion
>  ## for each InternalTimer, add 2 more properties: create version and delete version
beside 3 existing properties: timestamp, key and namespace. each time a Timer is registered
in timerservice, it is created with stateTableVersion as its create version while delete version
is -1. each time when timer is deleted in timerservice, it is marked delete for giving it
a delete verison equals to stateTableVersion without physically delete it from timerservice.
>  ## each time when try to snapshot timers, InternalTimeServiceManager increase its stateTableVersion
and add this stateTableVersion in snapshotVersions. these 2 operators are protected by write
lock of InternalTimeServiceManager. that current stateTableVersion take as snapshot version
of this snapshot
>  ## shallow copy <String,HeapInternalTimerService> tuples
>  ## then use a another thread asynchronous snapshot whole things: keyserialized, namespaceserializer
and timers. for timers which is not deleted(delete version is -1) and create version less
than snapshot version, serialized it. for timers whose delete version is not -1 and is bigger
than or equals snapshot version, serialized it. otherwise, it will not be serialized by this
>  ## when everything is serialized, remove snapshot version in snapshotVersions, which
is still in another thread and this action is guarded by write lock.
>  ## last thing: timer physical deletion. 2 places to physically delete timers: each time
when timer is deleted in timerservice, it is marked delete for giving it a delete verison
equals to stateTableVersion without physically delete it from timerservice. after this, check
if snapshotVersions size is 0 (which means there is no running snapshot) and if true, delete
timer .the other place to delete is in snapshot timer's iterat: when timer's delete version
is less than min value of snapshotVersions, which means the timer is deleted and no running
snapshot should keep it.
>  ## some more additions: processingTimeTimers and eventTimeTimers for each group used
to be hashset and now it is changed to concurrenthashmap with key+namesapce+timestamp as its
hash key.
>  # related mail list thread
>  ## http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Slow-flink-checkpoint-td18946.html
>  # github pull request
>  ## //coming soon

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