BartMiki opened a new pull request, #15754: URL: https://github.com/apache/druid/pull/15754
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See [the 'If your pull request shows conflicts with master' section](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#if-your-pull-request-shows-conflicts-with-master) for more details. --> Fixes #15069. <!-- If you are a committer, follow the PR action item checklist for committers: https://github.com/apache/druid/blob/master/dev/committer-instructions.md#pr-and-issue-action-item-checklist-for-committers. --> ### Description This PR fixes #15069 by resolving a memory leak caused by a thread leak in `query-cancellation-executor`. #### Root of the bug The problem was caused by removal of queryable server from a Broker list. Some of the servers have a DirectQueryRunner that creates `SingleThreadedScheduledExecutor`. In a case when native query was cancelled a thread would be created. However, when the server was removed from the list we lost a reference to the server view that holds the runner that holds executor. When at least one query was cancelled, but the reference was lost, then the thread would be waiting infinitely, with no possibility to GC it. There was no cleanup of the executor. #### Solution * Add `AutoClosable` to `QueryRunner` with default empty implementation - this way all functional interfaces implementation are still correct. * Add timeout of 5 minutes to one of the `future.get` methods that were blocking indefinitely (and they were in our clients case) in `DruidDirectClient`. * Implement `close` in `DruidDirectClient` that properly shuts down a thread pool. * Invoke `close` in removal of the `QueryableDruidServer` from the `BrokerServerView`. #### Reproducing To reproduce this bug before the patch, we need to have a standard Druid cluster (for example `micro quickstart`) with one broker and one historical. We want to monitor Broker threads (for example with: `jconsol`). We need to have a command to spin up a second historical. Then the steps to reproduce are: 1. Execute a long running native query and cancel it - this should trigger creation of the `query-cancellation-executor` thread. There should be only _one_ thread now. 2. Start another historical. 3. Execute a long running native query and cancel it - there should be _two_ of these threads 4. Kill this 2nd historical - we still should have two threads on a list 5. Start 2nd historical again 6. Execute a long running native query and cancel it - there should be _three_ of these threads 7. Thread leak detected, as we have 2 historical nodes, but 3 threads. 8. Repeat kill, start, execute, cancel to get more threads. #### Release note Fixed: DirectDruidClient no longer leaks query-cancellation-executor threads after being removed by BrokerServerView. <hr> ##### Key changed/added classes in this PR * `QueryRunner` * `DruidDirectClient` * `BrokerServerView` * `QueryableDruidServer` <hr> <!-- Check the items by putting "x" in the brackets for the done things. 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Linked related entities via Javadoc links. - [ ] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md) - [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader. - [ ] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for [code coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md) is met. - [ ] added integration tests. - [x] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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