siddhantsangwan commented on code in PR #3423:
URL: https://github.com/apache/ozone/pull/3423#discussion_r881458132
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hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/balancer/ContainerBalancer.java:
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@@ -801,24 +846,70 @@ private void resetState() {
/**
* Receives a notification for raft or safe mode related status changes.
* Stops ContainerBalancer if it's running and the current SCM becomes a
- * follower or enters safe mode.
+ * follower or enters safe mode. Starts ContainerBalancer if the current
+ * SCM becomes leader, is out of safe mode and balancer should run.
*/
@Override
public void notifyStatusChanged() {
- if (!scmContext.isLeader() || scmContext.isInSafeMode()) {
- if (isBalancerRunning()) {
- stopBalancingThread();
+ lock.lock();
+ try {
+ if (!scmContext.isLeader() || scmContext.isInSafeMode()) {
+ if (isBalancerRunning()) {
+ stop();
+ }
+ } else {
+ if (shouldRun()) {
+ try {
+ start();
+ } catch (IllegalContainerBalancerStateException |
+ InvalidContainerBalancerConfigurationException e) {
+ LOG.warn("Could not start ContainerBalancer on raft/safe-mode " +
+ "status change.", e);
+ }
+ }
}
+ } finally {
+ lock.unlock();
}
}
/**
- * Checks if ContainerBalancer should run.
- * @return false
+ * Checks if ContainerBalancer should start (after a leader change, restart
+ * etc.) by reading persisted state.
+ * @return true if the persisted state is true, otherwise false
*/
@Override
public boolean shouldRun() {
- return false;
+ try {
Review Comment:
Since we're already reading the persisted status for telling whether
balancer should run, we probably don't need to check and update ServiceStatus.
The persisted status is the most reliable information in balancer's case since
it's not a background service.
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