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https://issues.apache.org/jira/browse/ZOOKEEPER-3408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16854253#comment-16854253
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Alexander Shraer commented on ZOOKEEPER-3408:
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There were some discussions about this on the mailing list, eg.,
[http://zookeeper-user.578899.n2.nabble.com/forceSync-no-td7577568.html]
IMHO a single reboot and leader re-election could lead to data loss if data
isn't synced to disk - imagine 5 servers. A transaction committed to 3 out of
5, and one of those 3 reboots. Now 3 out of 5 servers don't have that
transaction and could cause that transaction to be truncated from the logs of
the other 2 servers. Maybe someone can correct me if I'm wrong here.
> Improve information about risks for forceSync config option
> -----------------------------------------------------------
>
> Key: ZOOKEEPER-3408
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3408
> Project: ZooKeeper
> Issue Type: Improvement
> Components: documentation
> Reporter: Dmitry Konstantinov
> Priority: Minor
>
> [https://zookeeper.apache.org/doc/r3.5.5/zookeeperAdmin.html#Unsafe+Options]
> {quote}
> The following options can be useful, but be careful when you use them. The
> risk of each is explained along with the explanation of what the variable
> does.
> {quote}
> {quote}
> _forceSync_ : (Java system property: *zookeeper.forceSync*) Requires updates
> to be synced to media of the transaction log before finishing processing the
> update. If this option is set to no, ZooKeeper will not require updates to be
> synced to the media.
> {quote}
> The risks for this option are not very clear. Does it only the risk of loss
> some recent committed transactions if all Zookeeper instances from an
> ensemble are crashed and restarted at almost the same time or some other
> problems are also possible?
>
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