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From "Ivan Rakov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-8761) WAL fsync at rollover should be asynchronous in LOG_ONLY and BACKGROUND modes
Date Tue, 17 Jul 2018 16:02:00 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-8761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16546821#comment-16546821
] 

Ivan Rakov commented on IGNITE-8761:
------------------------------------

[~v.pyatkov], I've looked through your changes. A few comments:
1) Seems like WalSegmentSyncer mimics behavior of FileWriteAheadLogManager#flush. Can we just
call external flush from fsyncer thread?
2) Current implementation stops WalSegmentSyncer through interruption. Please look at shutdown
mechanism of other WAL threads.
3) Potential StorageException during fsync is not handled
4) Why we need to use ConcurrentLinkedHashMap here? I don't see how it's related to the original
issue.

> WAL fsync at rollover should be asynchronous in LOG_ONLY and BACKGROUND modes
> -----------------------------------------------------------------------------
>
>                 Key: IGNITE-8761
>                 URL: https://issues.apache.org/jira/browse/IGNITE-8761
>             Project: Ignite
>          Issue Type: Improvement
>          Components: persistence
>            Reporter: Ivan Rakov
>            Assignee: Vladislav Pyatkov
>            Priority: Major
>             Fix For: 2.7
>
>
> Transactions may periodically hang for a few seconds in LOG_ONLY or BACKGROUND persistent
modes. Thread dumps show that threads are hanging on syncing previous WAL segment during rollover:
> {noformat}
>   java.lang.Thread.State: RUNNABLE
>    at java.nio.MappedByteBuffer.force0(MappedByteBuffer.java:-1)
>    at java.nio.MappedByteBuffer.force(MappedByteBuffer.java:203)
>    at org.apache.ignite.internal.processors.cache.persistence.wal.FileWriteAheadLogManager$FileWriteHandle.close(FileWriteAheadLogManager.java:2843)
>    at org.apache.ignite.internal.processors.cache.persistence.wal.FileWriteAheadLogManager$FileWriteHandle.access$600(FileWriteAheadLogManager.java:2483)
>    at org.apache.ignite.internal.processors.cache.persistence.wal.FileWriteAheadLogManager.rollOver(FileWriteAheadLogManager.java:1094)
> {noformat}
> Waiting for this fsync is not necessary action to ensure crash recovery guarantees. Instead
of this, we should just perform fsyncs asychronously and ensure that they are completed prior
to next checkpoint start.



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