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https://issues.apache.org/jira/browse/HBASE-24?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613104#action_12613104
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stack commented on HBASE-24:
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Thanks for doing the profiling LN. Do you think we should put an upper bound
on the number of regions a particular regionserver can carry at any one time or
an upper bound on number of open Readers? I wonder, if you want to carry many
regions, if lowering the compaction threshold from 3 to 2 -- or even to 1 --
would make any difference in our memory profile (at a CPU cost)? We load the
index and keep it around to avoid doing it on each random access -- maybe if a
bounded pool of open MapFiles, we could move files in and out of the pool on
some kind of LRU basis?
> Scaling: Too many open file handles to datanodes
> ------------------------------------------------
>
> Key: HBASE-24
> URL: https://issues.apache.org/jira/browse/HBASE-24
> Project: Hadoop HBase
> Issue Type: Bug
> Components: regionserver
> Reporter: stack
> Priority: Critical
>
> 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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