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From "Andrey Gura (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-7408) Document WAL changes
Date Thu, 25 Jan 2018 14:40:00 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-7408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16339298#comment-16339298

Andrey Gura commented on IGNITE-7408:

I've looked at docs and have only one comment about WAL mode BACKGROUND description. 

"If the memory-mapped file approach is disabled then the changes are flushed to the node's
internal buffer periodically."

Actually changes will be flushed to the file from internal buffer but will not be fsync'ed.
So OS will be responsible for writing changes to the disk device.

> Document WAL changes
> --------------------
>                 Key: IGNITE-7408
>                 URL: https://issues.apache.org/jira/browse/IGNITE-7408
>             Project: Ignite
>          Issue Type: Task
>          Components: documentation
>            Reporter: Andrey Gura
>            Assignee: Andrey Gura
>            Priority: Major
>              Labels: documentation
>             Fix For: 2.4
> WAL documentation should be updated accordingly to IGNITE-6339 issue.
> The following changes can affect WAL configuration and behavior:
>  # {{DataStorageConfiguration.setWalBufferSize}} added instead of {{PersistentStoreConfiguration.setTlbSize}}.
By default WAL buffer size equals WAL segment size if memory mapped file is enabled, and (WAL
segment size) / 4 if memory mapped file is disabled.
>  # Memory mapped file is enabled by default and provides better performance. Memory mapped
file usage can be turned off. {{IGNITE_WAL_MMAP}} property with {{false}} value should be
added to the JVM arguments: {{-DIGNITE_WAL_MMAP=false}}.
>  # If memory mapped file is enabled then {{BACKGROUND}} and {{LOG_ONLY}} WAL modes behave
identically and don't have any differences in performance or data integrity guarantees.

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