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https://issues.apache.org/jira/browse/HBASE-2669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875963#action_12875963
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Benoit Sigoure commented on HBASE-2669:
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As you wrote Stack, there's no easy way to get to the HCM's hook. First of
all, the HCM itself doesn't retain a reference to it, so right now it's just
impossible to reach. Even if a reference was retained, the
{{suppressHdfsShutdownHook}} hack in {{HRegionServer}} seems too ugly and
fragile to me. We don't need to expose this internal implementation detail of
the HCM to user. Instead we can just have a static method in {{HTable}} that
the user can call to perform a graceful shutdown.
But I also doubt this hook is useful at all. As I said, I'm not sure we need
to properly close the connections ourselves. The OS will take care of them
anyway, and whatever the client was talking to will be notified that the socket
was closed on the other side. Maybe we can just remove the hook altogether and
get away with it.
BTW, sorry I didn't mean to close 0.20.5 with this issue, I'm working with
{{trunk}} so this has nothing to do with 0.20.5 anyway. I also noticed that
{{suppressHdfsShutdownHook}} has gone away in trunk. Not sure why, but that's
a good thing.
> HCM.shutdownHook causes data loss with hbase.client.write.buffer != 0
> ---------------------------------------------------------------------
>
> Key: HBASE-2669
> URL: https://issues.apache.org/jira/browse/HBASE-2669
> Project: HBase
> Issue Type: Bug
> Components: client
> Reporter: Benoit Sigoure
> Assignee: Benoit Sigoure
> Priority: Critical
> Fix For: 0.21.0
>
>
> In my application I set {{hbase.client.write.buffer}} to a reasonably small
> value (roughly 64 edits) in order to try to batch a few {{Put}} together
> before talking to HBase. When my application does a graceful shutdown, I
> call {{HTable#flushCommits}} in order to flush any pending change to HBase.
> I want to do the same thing when I get a {{SIGTERM}} by using
> {{Runtime#addShutdownHook}} but this is impossible since
> {{HConnectionManager}} already registers a shutdown hook that invokes
> {{HConnectionManager#deleteAllConnections}}. This static method closes all
> the connections to HBase and then all connections to ZooKeeper. Because all
> shutdown hooks run in parallel, my hook will attempt to flush edits while
> connections are getting closed.
> There is no way to guarantee the order in which the hooks will execute, so I
> propose that we remove the hook in the HCM altogether and provide some
> user-visible API they call in their own hook after they're done flushing
> their stuff, if they really want to do a graceful shutdown. I expect that a
> lot of users won't use a hook though, otherwise this issue would have cropped
> up already. For those users, connections won't get "gracefully" terminated,
> but I don't think that would be a problem since the underlying TCP socket
> will get closed by the OS anyway, so things like ZooKeeper and such should
> realize that the connection has been terminated and assume the client is
> gone, and do the necessary clean-up on their side.
> An alternate fix would be to leave the hook in place by default but keep a
> reference to it and add a user-visible API to be able to un-register the
> hook. I find this ugly.
> Thoughts?
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