CDC/etcd_worker: add rate limiter to limit EtcdWorker tick frequency

[asddongmen]

What problem does this PR solve?

#3112
Too frequent etcd worker tick will cause etcd to be overburdened, and the current etcd qps will increase exponentially with the number of tables that need to be replicated.

What is changed and how it works?

Add rate limiter to limit EtcdWorker ticks frequency.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Summary: Limiting the tick frequency of EtcdWoker can reduce etcd qps by about 50%, but it will reduce the replication speed by about 20%.

Test Environment:

1. 2 Machines: 8-core 16G memory 500G high-speed disk
2. Sink Type: mysql
3. Cluster topo:

pd_servers:
  - host: 172.x.x.x
  - host: 172.x.x.x

tidb_servers:
  - host: 172.x.x.x
  - host: 172.x.x.x
    
tikv_servers:
  - host: 172.x.x.x
  - host: 172.x.x.x

cdc_servers:
  - host: 172.x.x.x
  - host: 172.x.x.x

monitoring_servers:
  - host: 172.x.x.x

grafana_servers:
  - host: 172.x.x.x

alertmanager_servers:
  - host: 172.x.x.x

Test1 (EtcdWorker ticks limit 10 times / s)
Create 16 changefeeds, synchronize a table for each, and write 50w rows of data to each table in upstream.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	3.3 min	1.1min	320	164%	4 min
processor	-	-	160	82%	-

Test2 (EtcdWorker ticks limit 10 times / s)
Create 30 changefeeds, synchronize a table for each, and write 50w rows of data to each table in upstream.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	6.8 min	5 min	600	189%	10 min
processor	-	-	300	95%	-

Test3 (EtcdWorker ticks without limit )
Create 16 changefeeds, synchronize a table for each, and write 50w rows of data to each table in upstream.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	2.74 min	50 s	630	193%	3 min
processor	-	-	260	92%	-

Test4 (EtcdWorker ticks without limit )
Create 30 changefeeds, synchronize a table for each, and write 50w rows of data to each table in upstream.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	6.9 min	3 min	1180	199%	8 min
processor	-	-	600	100%	-

Test5 (Incremental scan、EtcdWorker ticks limit 10 times / s)

1. Create 30 changefeed and pause.
2. 30 tables are created upstream, and 50w data is written into each table.
3. After waiting for the upstream data to be written, resume the above 30 changefeeds.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	7 min	4 min	600	400%	9 min
processor	-	-	300	200%	-

Test6 (Incremental scan、EtcdWorker ticks limit 10 times / s)

1. Create 30 changefeed and pause.
2. 30 tables are created upstream, and 50w data is written into each table.
3. After waiting for the upstream data to be written, resume the above 30 changefeeds.

When resume changefeed, the owner was down instantly.

	Max checkpoint lag	Average checkpoint lag in peak	Max etcd qps	CPU usage	Total synchronization time
owner	10 min	7 min	871	400%	10 min
processor	-	-	658	200%	-

Side effects

• Has exported variable changed.
• Possible performance regression

Related changes

• Need to cherry-pick to the release branch

Release note

Please add a release note.
If you don't think this PR needs a release note then fill it with `None`.

[ti-chi-bot]

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• liuzix
• overvenus

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[asddongmen]

/run-all-tests

[maxshuang]

the current etcd qps will increase exponentially with the number of tables that need to be replicated.

----- @asddongmen could u explain why?

This pr is a workaround or a solution?

[maxshuang]

I still can't get the point of your tests. "write 50w rows of data to each table in upstream" means a heavy continuous flow in upstream, so it is reasonable to increase the etcdworker ticks to speed up.

Am I right? Or merge some resolvedTs or checkpointTs report will be a better solution? instead of just limit the rate.

[liuzix]

I still can't get the point of your tests. "write 50w rows of data to each table in upstream" means a heavy continuous flow in upstream, so it is reasonable to increase the etcdworker ticks to speed up.

Am I right? Or merge some resolvedTs or checkpointTs report will be a better solution? instead of just limit the rate.

From what I understand, the point of this PR is to address the problem that, within a given period, the number of ticks in one node must be greater than or equal to the number of updates by all nodes. This behavior is not optimal from a very low level.

If you mean batching updates for different changefeeds by "merge some resolvedTs or checkpointTs report", I think this will be a different optimization. The behavior of the business logic is orthogonal to what we are trying to fix here. We can investigate your proposal and address it in another PR.

[liuzix]

/run-integration-tests

[codecov-commenter]

Codecov Report

Merging #3219 (9adb87d) into master (3c3b915) will decrease coverage by 0.3558%.
The diff coverage is 51.4877%.

@@               Coverage Diff                @@
##             master      #3219        +/-   ##
================================================
- Coverage   57.2251%   56.8692%   -0.3559%     
================================================
  Files           163        211        +48     
  Lines         19453      22768      +3315     
================================================
+ Hits          11132      12948      +1816     
- Misses         7261       8493      +1232     
- Partials       1060       1327       +267     

[overvenus]

/merge

[ti-chi-bot]

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

Commit hash: ea892d8

[liuzix]

/run-all-tests

[amyangfei]

/merge

[asddongmen]

/run-dm-integration-tests

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3267.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3268.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3269.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3270.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3271.

[Rustin170506]

@asddongmen You don't seem to have filled out the release note correctly, so please fill out the release note for the next fix.