Jayush Luniya created AMBARI-14671:
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Summary: Reevaluate the use of threadpools in Ambari code base
Key: AMBARI-14671
URL: https://issues.apache.org/jira/browse/AMBARI-14671
Project: Ambari
Issue Type: Bug
Components: ambari-server
Affects Versions: 2.2.0
Reporter: Jayush Luniya
Assignee: Jayush Luniya
Fix For: 2.4.0
As part of investigation for BUG-43981, noticed that in many places in the
Ambari code base, the way we use the threadpool is not quite correct. We will
never scale up the number of threads on high load when we use unbounded queues.
This could lead to performance bottlenecks especially if we are configure
ThreadPoolExecutor with corePoolSize=0 and maxPoolSize=10, only one thread will
ever be spawned. See observations below
Observations:
1. When a ThreadPoolExecutor object is created, the pool size is 0 (i.e. no new
threads are created then) unless prestartAllCoreThreads() is called. Also if we
set allowCoreThreadTimeOut(true), idle core threads will also be reclaimed.
2. In our code base, I observed that we create a threadpool using unlimited
queue. However the pool will never scale up from coreThreads -> maxThreads as
the request will always get queued.
{code:java}
LinkedBlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>(); //
unlimited Queue
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(
THREAD_POOL_CORE_SIZE,
THREAD_POOL_MAX_SIZE,
THREAD_POOL_TIMEOUT_MILLIS,
TimeUnit.MILLISECONDS,
queue);
{code}
http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ThreadPoolExecutor.html
{quote}
Unbounded queues. Using an unbounded queue (for example a LinkedBlockingQueue
without a predefined capacity) will cause new tasks to wait in the queue when
all corePoolSize threads are busy. Thus, no more than corePoolSize threads will
ever be created. (And the value of the maximumPoolSize therefore doesn't have
any effect.) This may be appropriate when each task is completely independent
of others, so tasks cannot affect each others execution; for example, in a web
page server. While this style of queuing can be useful in smoothing out
transient bursts of requests, it admits the possibility of unbounded work queue
growth when commands continue to arrive on average faster than they can be
processed.
{quote}
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