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https://issues.apache.org/jira/browse/CASSANDRA-19328?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stefan Miklosovic updated CASSANDRA-19328:
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Summary: Incorrect return value of getMaxTasksQueued in
ThreadPoolExecutorPlus (was: Incorrect return value getMaxTasksQueued in
ThreadPoolExecutorPlus)
> Incorrect return value of getMaxTasksQueued in ThreadPoolExecutorPlus
> ---------------------------------------------------------------------
>
> Key: CASSANDRA-19328
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19328
> Project: Cassandra
> Issue Type: Bug
> Components: Legacy/Core, Observability/Metrics
> Reporter: Stefan Miklosovic
> Priority: Normal
>
> While working on CASSANDRA-19289, I got wrong results there. I was attempting
> to add core_pool_size, max_pool_size and max_tasks_queued to the output of
> system_views.thread_pools but initially I got this:
>
> {noformat}
> cqlsh> select name, core_pool_size, max_pool_size,
> max_tasks_queued,pending_tasks from system_views.thread_pools;
> name | core_pool_size | max_pool_size |
> max_tasks_queued | pending_tasks
> --------------------------------+----------------+---------------+------------------+---------------
> CacheCleanupExecutor | 1 | 1 |
> 0 | 0
> CompactionExecutor | 2 | 2 |
> 0 | 0
> GossipStage | 1 | 1 |
> 0 | 0
> HintsDispatcher | 2 | 2 |
> 0 | 0
> MemtableFlushWriter | 2 | 2 |
> 0 | 0
> MemtablePostFlush | 1 | 1 |
> 0 | 0
> MemtableReclaimMemory | 1 | 1 |
> 0 | 0
> Native-Transport-Auth-Requests | 0 | 4 |
> 2147483647 | 0
> Native-Transport-Requests | 0 | 128 |
> 2147483647 | 0
> PerDiskMemtableFlushWriter_0 | 2 | 2 |
> 0 | 0
> ReadStage | 0 | 32 |
> 2147483647 | 0
> Sampler | 1 | 1 |
> 0 | 0
> SecondaryIndexExecutor | 2 | 2 |
> 0 | 0
> SecondaryIndexManagement | 1 | 1 |
> 0 | 0
> StatusPropagationExecutor | 1 | 1 |
> 0 | 0
> ValidationExecutor | 2 | 2 |
> 0 | 0
> ViewBuildExecutor | 1 | 1 |
> 0 | 0
> {noformat}
> This is wrong on max_tasks_queued column. That "0" there is misleading. That
> number is fetched from here (1) but getQueue().size() is 0 when that queue
> does not have any tasks queued. It should be "getQueue().remainingCapacity()"
> which reflects the number of tasks that queue can hold until tasks will be
> rejected. That is what "max_tasks_queued" means in my books.
> getQueue().size() is used in ThreadPoolExecutorBase here
> {noformat}
> @Override
> public int getPendingTaskCount()
> {
> return getQueue().size();
> }
> {noformat}
> We are using getQueue().size() for two independent things.
> When I change it to "remainingCapacity()" it will report it like this:
> {noformat}
> cqlsh> select name, core_pool_size, max_pool_size,
> max_tasks_queued,pending_tasks from system_views.thread_pools;
> name | core_pool_size | max_pool_size |
> max_tasks_queued | pending_tasks
> --------------------------------+----------------+---------------+------------------+---------------
> CacheCleanupExecutor | 1 | 1 |
> 2147483647 | 0
> CompactionExecutor | 2 | 2 |
> 2147483647 | 0
> GossipStage | 1 | 1 |
> 2147483647 | 0
> HintsDispatcher | 2 | 2 |
> 2147483647 | 0
> MemtableFlushWriter | 2 | 2 |
> 2147483647 | 0
> MemtablePostFlush | 1 | 1 |
> 2147483647 | 0
> MemtableReclaimMemory | 1 | 1 |
> 2147483647 | 0
> Native-Transport-Auth-Requests | 0 | 4 |
> 2147483647 | 0
> Native-Transport-Requests | 0 | 128 |
> 2147483647 | 0
> PerDiskMemtableFlushWriter_0 | 2 | 2 |
> 2147483647 | 0
> ReadStage | 0 | 32 |
> 2147483647 | 0
> Sampler | 1 | 1 |
> 1000 | 0
> SecondaryIndexExecutor | 2 | 2 |
> 2147483647 | 0
> SecondaryIndexManagement | 1 | 1 |
> 2147483647 | 0
> StatusPropagationExecutor | 1 | 1 |
> 2147483647 | 0
> ValidationExecutor | 2 | 2 |
> 2147483647 | 0
> ViewBuildExecutor | 1 | 1 |
> 2147483647 | 0
> {noformat}
> So what happens in practice is that if there are some pending tasks, lets
> say, 100 of them, then max_tasks_queued will be Integer.MAX minus 100.
> cc [~benedict]
> (1)
> [https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/concurrent/ThreadPoolExecutorPlus.java#L123]
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