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https://issues.apache.org/jira/browse/HADOOP-2577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558268#action_12558268
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Chad Walters commented on HADOOP-2577:
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Perhaps we should just open the mapfiles as needed and measure the effect on
random reads. It could turn out that the effect is not that big, given that
random reads are not performing well anyway. Focusing on allowing folks to
scale up rather than performance on the random read use case seems like it
could be the right trade-off at the moment and give us some breathing room to
address the non-blocking IO issue at a more measured pace.
> [hbase] Scaling: Too many open file handles to datanodes
> --------------------------------------------------------
>
> Key: HADOOP-2577
> URL: https://issues.apache.org/jira/browse/HADOOP-2577
> Project: Hadoop
> Issue Type: Bug
> Components: contrib/hbase
> Reporter: stack
>
> We've been here before (HADOOP-2341).
> Today the rapleaf gave me an lsof listing from a regionserver. Had thousands
> of open sockets to datanodes all in ESTABLISHED and CLOSE_WAIT state. On
> average they seem to have about ten file descriptors/sockets open per region
> (They have 3 column families IIRC. Per family, can have between 1-5 or so
> mapfiles open per family -- 3 is max... but compacting we open a new one,
> etc.).
> They have thousands of regions. 400 regions -- ~100G, which is not that
> much -- takes about 4k open file handles.
> If they want a regionserver to server a decent disk worths -- 300-400G --
> then thats maybe 1600 regions... 16k file handles. If more than just 3
> column families..... then we are in danger of blowing out limits if they are
> 32k.
> We've been here before with HADOOP-2341.
> A dfsclient that used non-blocking i/o would help applications like hbase
> (The datanode doesn't have this problem as bad -- CLOSE_WAIT on regionserver
> side, the bulk of the open fds in the rapleaf log, don't have a corresponding
> open resource on datanode end).
> Could also just open mapfiles as needed, but that'd kill our random read
> performance and its bad enough already.
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