Fix the tasks in bkg pool may be called more frequently than expected

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #6908

Problem Summary:
When we add a task into BackgroundProcessingPool which always return false, we expect that will be run at a fixed interval. (Almost fixed within small random the BackgroundProcessingPool random part)

However, a task may be popped into multiple threads and they can run the task one by one. That leads to more frequent calls than expected.
We have to add extra logic to avoid the task being unexpectedly called too frequently. That is annoying.

• this is a known isssue
  

  tiflash/dbms/src/Storages/BackgroundProcessingPool.h

  Lines 92 to 98 in e1418dc

  	/// But at each scheduled time, there may be multiple threads try to run the same task,
  	/// and then execute the same task one by one in sequential order(not simultaneously) even if `multi` is false.
  	/// For example, consider the following case when it's time to schedule a task,
  	/// 1. thread A get the task, mark the task as occupied and begin to execute it
  	/// 2. thread B also get the same task
  	/// 3. thread A finish the execution of the task quickly, release the task and try to update the next schedule time of the task
  	/// 4. thread B find the task is not occupied and execute the task again almost immediately

• extra codes to handle unexpected frequent calls
  

  tiflash/dbms/src/Storages/Page/V3/Universal/UniversalPageStorageService.cpp

  Lines 38 to 45 in e1418dc

  	bool UniversalPageStorageService::gc()
  	{
  	Timepoint now = Clock::now();
  	const std::chrono::seconds try_gc_period(30);
  	if (now < (last_try_gc_time.load() + try_gc_period))
  	return false;
  	last_try_gc_time = now;

  
  

  tiflash/dbms/src/Storages/DeltaMerge/StoragePool.cpp

  Lines 146 to 156 in e1418dc

  	bool GlobalStoragePool::gc(const Settings & settings, bool immediately, const Seconds & try_gc_period)
  	{
  	Timepoint now = Clock::now();
  	if (!immediately)
  	{
  	// No need lock
  	if (now < (last_try_gc_time.load() + try_gc_period))
  	return false;
  	}
  	last_try_gc_time = now;

What is changed and how it works?

Change one member of Task from atomic<bool> occupied into size_t concurrent_executors. concurrent_executors
indicate how many worker threads are holding this task.

• If task.multi == false, only when task.concurrent_executor == 0, can the task pop to a worker thread for executing
• Changing to task.concurrent_executor is protected under the lock of pool.tasks_mutex

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  • port these changes to s3gc branch and check the frequency of etcd keepalive and s3gc being called
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• flowbehappy
• lidezhu

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[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/run-sanitizer-test tsan

[JaySon-Huang]

https://ci.pingcap.net/blue/organizations/jenkins/tiflash-sanitizer-daily/detail/tiflash-sanitizer-daily/917/pipeline

[flowbehappy]

LGTM

[JaySon-Huang]

/run-all-tests

[lidezhu]

LGTM

[JaySon-Huang]

/merge

[ti-chi-bot]

@JaySon-Huang: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: dae3603