frankmu opened a new pull request, #2846:
URL: https://github.com/apache/helix/pull/2846
### Issues
- [x] My PR addresses the following Helix issues and references them in the
PR description:
resolves #2822
### Description
- [x] Here are some details about my PR, including screenshots of any UI
changes:
This PR initiates the condition based rebalancer which can perform
restricted shard shuffling based on conditions. Will add more tests if the
overall skeleton makes sense. Sample code to trigger the rebalance with
condition `if (event type is CurrentStateChange OR CurrentStateChange)`
```
RebalanceCondition condition = new RebalanceConditionBuilder()
.addCondition(() ->
event.getEventType().equals(ClusterEventType.ClusterConfigChange))
.addCondition(() ->
event.getEventType().equals(ClusterEventType.CurrentStateChange))
.buildOr();
Rebalancer rebalancer = new ConditionBasedRebalancer(condition);
```
We can also do nested condition as following:
```
BooleanSupplier condition1 = () -> 5 > 3;
BooleanSupplier condition2 = () -> 2 > 3;
BooleanSupplier condition3 = () ->
event.getEventType().equals(ClusterEventType.ClusterConfigChange);
BooleanSupplier condition4 = () ->
event.getEventType().equals(ClusterEventType.CurrentStateChange);
RebalanceCondition andCondition = new RebalanceConditionBuilder()
.addCondition(condition1)
.addCondition(condition3)
.buildAnd();
RebalanceCondition orCondition = new RebalanceConditionBuilder()
.addCondition(condition2)
.addCondition(condition4)
.buildOr();
RebalanceCondition nestedCondition = new RebalanceConditionBuilder()
.addAndCondition(andCondition, orCondition)
.buildAnd();
Rebalancer rebalancer = new ConditionBasedRebalancer(condition);
```
### Tests
- [x] The following tests are written for this issue:
N/A
- The following is the result of the "mvn test" command on the appropriate
module:
(If CI test fails due to known issue, please specify the issue and test PR
locally. Then copy & paste the result of "mvn test" to here.)
### Changes that Break Backward Compatibility (Optional)
- My PR contains changes that break backward compatibility or previous
assumptions for certain methods or API. They include:
(Consider including all behavior changes for public methods or API. Also
include these changes in merge description so that other developers are aware
of these changes. This allows them to make relevant code changes in feature
branches accounting for the new method/API behavior.)
### Documentation (Optional)
- In case of new functionality, my PR adds documentation in the following
wiki page:
(Link the GitHub wiki you added)
### Commits
- My commits all reference appropriate Apache Helix GitHub issues in their
subject lines. In addition, my commits follow the guidelines from "[How to
write a good git commit message](http://chris.beams.io/posts/git-commit/)":
1. Subject is separated from body by a blank line
1. Subject is limited to 50 characters (not including Jira issue reference)
1. Subject does not end with a period
1. Subject uses the imperative mood ("add", not "adding")
1. Body wraps at 72 characters
1. Body explains "what" and "why", not "how"
### Code Quality
- My diff has been formatted using helix-style.xml
(helix-style-intellij.xml if IntelliJ IDE is used)
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