[jira] [Created] (IMPALA-9638) Don't create unnecessary threads in executor-only impalads

["Sahil Takiar (Jira)" <ji...@apache.org>]

Sahil Takiar created IMPALA-9638:
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             Summary: Don't create unnecessary threads in executor-only impalads
                 Key: IMPALA-9638
                 URL: https://issues.apache.org/jira/browse/IMPALA-9638
             Project: IMPALA
          Issue Type: Improvement
          Components: Backend
            Reporter: Sahil Takiar


Looking through the code for ImpalaServer, it looks like there are several threads / thread-pools that are started on executor-only impalads, but don't actually do anything:
 * The "cancellation-worker" threadpool (ImpalaServer::CancelFromThreadPool)
 * The "session-maintenance" thread (ImpalaServer::SessionMaintenance)
 * The "query-expirer" thread (ImpalaServer::ExpireQueries)
 * The "unresponsive-backend-thread" thread (ImpalaServer::UnresponsiveBackendThread)
 * The code to start ImpalaInternalService might be dead code, but maybe we should just delete it since the ImpalaInternalService doesn't exist anymore

Confirmed this my creating a cluster with dedicated coordinator and getting a thread dump of an executor, which showed the following:
{code:java}
Thread 16 (Thread 0x7fe96fe57700 (LWP 8721)):
#0  0x00007fea1ad20360 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0
No symbol table info available.
#1  0x0000000001ce4423 in impala::ConditionVariable::Wait (this=0x110b3370, lock=...) at /home/stakiar/Impala/be/src/util/condition-variable.h:49
        mutex = 0x110b3348
#2  0x0000000002469f6a in impala::ImpalaServer::SessionMaintenance (this=0x110b3200) at /home/stakiar/Impala/be/src/service/impala-server.cc:2055
        timeout_lock = {_M_device = 0x110b3348, _M_owns = true}
        now = 140640581412928
        expired_cnt = 0 {code}



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