feat: protect datanode with concurrency limit. #4699

lyang24 · 2024-09-09T05:16:36Z

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What's changed and what's your intention?

Adding query parallelism limit in region server to protect datanode from query overload.

Checklist

I have written the necessary rustdoc comments.
I have added the necessary unit tests and integration tests.
This PR requires documentation updates.

coderabbitai · 2024-09-09T05:16:42Z

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src/datanode/src/region_server.rs

codecov · 2024-09-11T04:15:03Z

Codecov Report

Attention: Patch coverage is 96.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.63%. Comparing base (67fb3d0) to head (75c340a).
Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4699      +/-   ##
==========================================
- Coverage   84.79%   84.63%   -0.17%     
==========================================
  Files        1115     1116       +1     
  Lines      201197   201385     +188     
==========================================
- Hits       170612   170443     -169     
- Misses      30585    30942     +357

sunng87

Remember to update config docs when we finalize the names

src/datanode/src/config.rs

sunng87

LGTM

waynexia · 2024-09-18T03:49:25Z

config/config.md

@@ -335,6 +335,8 @@
 | `init_regions_in_background` | Bool | `false` | Initialize all regions in the background during the startup.<br/>By default, it provides services after all regions have been initialized. |
 | `enable_telemetry` | Bool | `true` | Enable telemetry to collect anonymous usage data. |
 | `init_regions_parallelism` | Integer | `16` | Parallelism of initializing regions. |
+| `max_concurrent_queries` | Integer | `0` | The maximum current queries allowed to be executed. Zero means unlimited. |
+| `concurrent_query_limiter_timeout` | String | `25ms` | The timeout of acquiring concurrency permits. |


Do we need this option? Despite the implementation details (acquire vs. try_acquire), it seems like users would hardly adjust this option. And exposing such an option would also limit us from implementing a better behavior in the future, like "only pending 30 awaiting requests in the queue, for at most 100ms".

We can hide such logic as our system's internal details. WDYT @sunng87 @evenyag

I agree remove this option will give better flexibility for future. I think try_acquire is a special case that is equivalent to 0 timeout on no permits i think having timeout maybe more flexible in this case. I removed the concurrent_query_limiter_timeout in DataNode options and hardcoded 25ms wait with a TODO. In future versions i think we could update the max_concurrent_queries and concurrent_query_limiter_timeout dynamically via sql such as SET max_concurrent_queries = 8;

src/datanode/src/region_server.rs

v0y4g3r · 2024-09-18T23:01:39Z

src/datanode/src/region_server.rs

+ if let Some(p) = &self.inner.parallelism {
+ let permit = p.acquire().await?;
+ let res = self.inner.handle_request(region_id, request).await;
+ drop(permit);
+ return res;
+ }


Looks like this semaphore also applies to RegionPutRequest whilst the purpose is to limit concurrent queries. We need to distinguish different request types.

should i put the rate limiting on handle_read and handle_remote_read that does datafusion queries? seems like handle_requests method is more of writes and region ddl changes.

v0y4g3r · 2024-09-18T23:04:01Z

src/datanode/src/datanode.rs

@@ -334,6 +334,9 @@ impl DatanodeBuilder {
 common_runtime::global_runtime(),
 event_listener,
 table_provider_factory,
+ opts.max_concurrent_queries,
+ //TODO: revaluate the hardcoded timeout on the next version of datanode concurrency limiter.
+ Duration::from_millis(25),


25ms seems to be too short. Maybe we need to hold those throttled queries instead of failing them very quickly.

I can increase the threshold. By hold do you mean to (worst case) allow queries to wait for the semaphore until the request to datanode timeout?

…erload.

github-actions bot added the docs-not-required This change does not impact docs. label Sep 9, 2024

sunng87 reviewed Sep 10, 2024

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src/datanode/src/region_server.rs Outdated Show resolved Hide resolved

lyang24 force-pushed the datanode_protection branch 4 times, most recently from ed16bbb to 724d851 Compare September 11, 2024 03:59

lyang24 marked this pull request as ready for review September 11, 2024 03:59

lyang24 requested a review from a team as a code owner September 11, 2024 03:59

lyang24 requested a review from sunng87 September 11, 2024 03:59

sunng87 reviewed Sep 11, 2024

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sunng87 requested a review from waynexia September 11, 2024 23:28

lyang24 force-pushed the datanode_protection branch 5 times, most recently from 2f755af to 0b101a3 Compare September 12, 2024 04:34

sunng87 approved these changes Sep 12, 2024

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waynexia reviewed Sep 18, 2024

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evenyag reviewed Sep 18, 2024

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lyang24 force-pushed the datanode_protection branch from 303d66f to 120224b Compare September 18, 2024 21:32

v0y4g3r reviewed Sep 18, 2024

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lyang24 force-pushed the datanode_protection branch from 120224b to 62a99c4 Compare September 19, 2024 00:48

Adding parallelism in region server to protect datanode from query ov…

75c340a

…erload.

lyang24 force-pushed the datanode_protection branch from 62a99c4 to 75c340a Compare September 19, 2024 01:10

killme2008 requested review from waynexia, evenyag and v0y4g3r September 22, 2024 03:33

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feat: protect datanode with concurrency limit. #4699

feat: protect datanode with concurrency limit. #4699

lyang24 commented Sep 9, 2024 •

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feat: protect datanode with concurrency limit. #4699

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