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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1736) If RS can't talk to master, pause; more importantly, don't split (Currently we do and splits are lost and table is wounded)
Date Tue, 16 Mar 2010 19:04:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12846074#action_12846074
] 

stack commented on HBASE-1736:
------------------------------

This issue is not as bad as it was.  We made a change so that if the RS fails to deliver message
to master, it'll retry rather than drop the message on the ground as it used to.

There is also the notion that loss of a split, while a pain, is not the end of the world.
 We can redo it if we have to.  There is some comment in the code in CompactSplitThread#split
where try to reason what happens to split if crash at various points along the split.  They
could do with review I'd say (smile).

On "It should add the children to the META before closing the parent, so that children are
not lost if RS crashes after closing parent", what are you thinking?  The parent would still
be online when we add in the daughter regions -- pre-close?  We'd have to deal then with clients
coming in and finding the daughter regions instead of the parent in .META.  (See how HRegion#getClosestRowBefore
works and then how its used in HCM#locateRegionInMeta).  We might have to add in some code
to not hand out daughter regions that don't have an info:server (They won't have an info:server
value in .META. if they have not deployed) but this will still be unsatisfactory since most
of the time it'll just end up with an offlined parent.

A related, big issue in here is currently closing the parent can take some time during which
attempts at reaching the parent region are rejected with NotServingRegionException.  Parents
can take a while to close because flush of memory content happens while the 'closing' flag
is set on the region.  Its as though we need to flush before we go into the close taking on
writes while we do so and then only flush the small amount we accumulated during the flush
while under the 'closing' flag (This is still unsatisfactory because if loaded system and
flushes are slow, memory might be filled by the time flush completes and again we'll have
a slow close because we're flushing lots of memory).  There is a 'make splits faster' issue
already.  I'm just calling attention to it here since it a little related.




> If RS can't talk to master, pause; more importantly, don't split (Currently we do and
splits are lost and table is wounded)
> ---------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-1736
>                 URL: https://issues.apache.org/jira/browse/HBASE-1736
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: stack
>            Assignee: stack
>            Priority: Critical
>             Fix For: 0.21.0
>
>
> What I saw was master shutting itself down because it had lost zk lease.  Fine.   The
RS though doesn't look like it can deal with this situation.    We'll see stuff like this:
> {code}
> ...failed on connection exception: java.net.ConnectException: Connection refused
>     at org.apache.hadoop.hbase.ipc.HBaseClient.wrapException(HBaseClient.java:744)
>     at org.apache.hadoop.hbase.ipc.HBaseClient.call(HBaseClient.java:722)
>     at org.apache.hadoop.hbase.ipc.HBaseRPC$Invoker.invoke(HBaseRPC.java:328)
>     at $Proxy0.regionServerReport(Unknown Source)
>     at org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:470)
>     at java.lang.Thread.run(Unknown Source)
> Caused by: java.net.ConnectException: Connection refused
>     at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
>     at sun.nio.ch.SocketChannelImpl.finishConnect(Unknown Source)
>     at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
>     at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:404)
>     at org.apache.hadoop.hbase.ipc.HBaseClient$Connection.setupIOstreams(HBaseClient.java:305)
>     at org.apache.hadoop.hbase.ipc.HBaseClient.getConnection(HBaseClient.java:826)
>     at org.apache.hadoop.hbase.ipc.HBaseClient.call(HBaseClient.java:707)
>     ... 4 more
> {code}
> ... all over the regionserver as it tries to send heartbeat to master on this broken
connection.
> On split, we close parent, add children to the catalog but then when we try to tell the
master about the split, it fails.  Means the children never get deployed.  Meantime  the parent
is offline.
> This issue is about going through the regionserver and anytime it has a connection to
master, make sure on fault that no damage is done the table and then that the regionserver
puts a pause on splitting.

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