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https://issues.apache.org/jira/browse/HBASE-9321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13751018#comment-13751018
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Devaraj Das commented on HBASE-9321:
------------------------------------
bq. If one connection per user, we may have many connections if there are many
users.
I would not be worried about supporting 100s of users each with their own
separate connection, from the REST server (assuming modest configuration of the
system). I'd suggest to start with, to reuse connections for the same user. If
you ask oozie folks, they will tell you about a cache they implemented in their
layer to deal with the many users problem (in their case they ended up creating
too many filesystem instances even for the same enduser). The cache is from
user -> ProxyUGI, right [~tucu00]?
I believe Hadoop core has done (or is doing) work to reuse connections for
multiple users (not sure whether the proxy users have been covered there).
I am +1 for both caching the "realuser" UGI and reusing connections across
different proxy-users for the same realuser within the RPC layer. Maybe, a good
one for 0.98?
> Contention getting the current user in RpcClient$Connection.writeRequest
> ------------------------------------------------------------------------
>
> Key: HBASE-9321
> URL: https://issues.apache.org/jira/browse/HBASE-9321
> Project: HBase
> Issue Type: Bug
> Affects Versions: 0.95.2
> Reporter: Jean-Daniel Cryans
> Fix For: 0.98.0, 0.96.0
>
> Attachments: trunk-9321.patch
>
>
> I've been running tests on clusters with "lots" of regions, about 400, and
> I'm seeing weird contention in the client.
> This one I see a lot, hundreds and sometimes thousands of threads are blocked
> like this:
> {noformat}
> "htable-pool4-t74" daemon prio=10 tid=0x00007f2254114000 nid=0x2a99 waiting
> for monitor entry [0x00007f21f9e94000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at
> org.apache.hadoop.security.UserGroupInformation.getCurrentUser(UserGroupInformation.java:466)
> - waiting to lock <0x00000000fb5ad000> (a java.lang.Class for
> org.apache.hadoop.security.UserGroupInformation)
> at
> org.apache.hadoop.hbase.ipc.RpcClient$Connection.writeRequest(RpcClient.java:1013)
> at org.apache.hadoop.hbase.ipc.RpcClient.call(RpcClient.java:1407)
> at
> org.apache.hadoop.hbase.ipc.RpcClient.callBlockingMethod(RpcClient.java:1634)
> at
> org.apache.hadoop.hbase.ipc.RpcClient$BlockingRpcChannelImplementation.callBlockingMethod(RpcClient.java:1691)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$BlockingStub.multi(ClientProtos.java:27339)
> at
> org.apache.hadoop.hbase.client.MultiServerCallable.call(MultiServerCallable.java:105)
> at
> org.apache.hadoop.hbase.client.MultiServerCallable.call(MultiServerCallable.java:43)
> at
> org.apache.hadoop.hbase.client.RpcRetryingCaller.callWithoutRetries(RpcRetryingCaller.java:183)
> {noformat}
> While the holder is doing this:
> {noformat}
> "htable-pool17-t55" daemon prio=10 tid=0x00007f2244408000 nid=0x2a98 runnable
> [0x00007f21f9f95000]
> java.lang.Thread.State: RUNNABLE
> at java.security.AccessController.getStackAccessControlContext(Native
> Method)
> at java.security.AccessController.getContext(AccessController.java:487)
> at
> org.apache.hadoop.security.UserGroupInformation.getCurrentUser(UserGroupInformation.java:466)
> - locked <0x00000000fb5ad000> (a java.lang.Class for
> org.apache.hadoop.security.UserGroupInformation)
> at
> org.apache.hadoop.hbase.ipc.RpcClient$Connection.writeRequest(RpcClient.java:1013)
> at org.apache.hadoop.hbase.ipc.RpcClient.call(RpcClient.java:1407)
> at
> org.apache.hadoop.hbase.ipc.RpcClient.callBlockingMethod(RpcClient.java:1634)
> at
> org.apache.hadoop.hbase.ipc.RpcClient$BlockingRpcChannelImplementation.callBlockingMethod(RpcClient.java:1691)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$BlockingStub.multi(ClientProtos.java:27339)
> at
> org.apache.hadoop.hbase.client.MultiServerCallable.call(MultiServerCallable.java:105)
> at
> org.apache.hadoop.hbase.client.MultiServerCallable.call(MultiServerCallable.java:43)
> at
> org.apache.hadoop.hbase.client.RpcRetryingCaller.callWithoutRetries(RpcRetryingCaller.java:183)
> {noformat}
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