[jira] [Updated] (TEZ-1187) Share Thread pools between different tasks

["Harish Jaiprakash (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/TEZ-1187?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Harish Jaiprakash updated TEZ-1187:
-----------------------------------
    Attachment: TEZ-1187.WIP.01.patch

[~sseth], Please take a look at this Shared Executor service:

* The service creates and uses a shared executor service underneath.
* It can create ScheduledExecutorService instances which behave almost like an ExecutorService. The differences are: 
- No support for a Single threaded executor service, which guarantees, serial execution of tasks.
- The shutdownNow does not return the non-scheduled Runnables.
- No fair scheduling b/w various ScheduledExecutorService instances created using the Shared Executor.

Currently the shared executor is a fixed thread pool executor. We can change it to CachedThreadPoolExecutor.

[~rajesh.balamohan] Had concerns with both the thread pool:
* With FixedThreadPool, all the threads can go into blocked state and a task which can unblock this will not be scheduled and can result in a deadlock.
* With cachedThreadPool, number of threads is not limited and can cause unbounded thread growth resulting in too many threads and system could end up in a crawl.

Another solution would be to create a thread pool which can monitor blocked threads and if all are in blocked state it will allocate newer threads and schedule tasks in them. And it will stop scheduling new tasks if too many runnable threads are active at a given time. This custom thread pool can also be used to ensure some fairness in scheduling of tasks.

> Share Thread pools between different tasks
> ------------------------------------------
>
>                 Key: TEZ-1187
>                 URL: https://issues.apache.org/jira/browse/TEZ-1187
>             Project: Apache Tez
>          Issue Type: Sub-task
>            Reporter: Siddharth Seth
>            Assignee: Harish Jaiprakash
>         Attachments: TEZ-1187.WIP.01.patch
>
>
> Thread pools are used all over for fetchers, sort etc. When running a single task - this is already a problem, and gets worse when running multiple tasks.



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