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https://issues.apache.org/jira/browse/KUDU-3364?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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shenxingwuying updated KUDU-3364:
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Attachment: image-2022-06-01-11-02-20-888.png
> Add TimerThread to ThreadPool to support a category of problem
> --------------------------------------------------------------
>
> Key: KUDU-3364
> URL: https://issues.apache.org/jira/browse/KUDU-3364
> Project: Kudu
> Issue Type: New Feature
> Reporter: shenxingwuying
> Assignee: shenxingwuying
> Priority: Minor
> Attachments: image-2022-06-01-11-02-20-888.png
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> h1. Scenanios
> In general, I am talking about a category of problem.
> There are some periodic tasks or automatically triggered scheduling tasks in
> kudu.
> For example, automatic rebalance of cluster data, some GC task and compaction
> tasks.
> Their implementation is by kudu Thread, maybe std::thread or ThreadPool, the
> really task internally periodic scheduled or internally strategy to trigge
> execution.
> They are all internal, we cann't do some.
> In fact, we need a method our control to trigge the above types of actions.
> In general, I am talking about a category of problem.
> Some scenarios is significant.
> Below is examples:
>
> h2. data rebalance
> There are two rebalance ways:
> 1. enable auto rebalance
> 2. use rebalance tool 1.14 before.
> The two ways maybe exist some conflicts at opeations race, because rebalance
> tool' logic is a litte complex at tool and auto rebalance is running at
> master.
> In future, auto rebalance at master will become very steady and become the
> main way for data rebalance. And at the same time, admin opers need a
> external trigger the rebalance just like auto rebalance.
> But, now auto rebalance is running in a thread and by time period.
> Although we can add a api for MasterService, but the api is synchronize, and
> will cose very much, we need a asynchronized method to trigger the rebalance.
> h2. auto compaction
> Another example is auto compaction,
> I have found compaction strategy is not always valid, so maybe we need a
> method controlled by admin users to triggle compaction.
> If we can do a RowSetInCompaction, we need not restart the kudu cluster.
> h1.
> h1. My Solution
> Add a timer in ThreadPool. This timer is a worker thread that schedules tasks
> to the specified thread according to time.
> We can limit only SERIAL ThreadPoolToken can enable TimerThread.
> Pseudo code expresses my intention：
> {code:java}
> //代码占位符
> class TimerThread {
> class Task {
> ThreadPoolToken token;
> std::function<void()> f;
> };
>
> void Schedule(Task task, int delay_ms) {
> tasks_.insert(...);
> }
> void RunLoop() {
> while (...) {
> SleepFor(100ms);
> tasks = FindTasks();
> for (auto task : tasks) {
> token = task.token;
> token->Submit(task.f);
> tasks_.erase...
> }
> }
> }
> scoped_refptr<Thread> thread_;
> std::multimap<MonoTime, Task> tasks;
> };
> class ThreadPool{
> ...
> TimerThread* timer_;
> ...
> };
> class ThreadPoolToken {
> void Scheduler();
> };{code}
> This scheme can be compatible with the previous ThreadPool, and timer is
> nullptr by default.
> For periodic tasks, We can use a Control ThreadPool with timer to refact some
> codes to make them more clear, to avoid the problem of too many single
> threads in the past.
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