[GitHub] [hbase] caroliney14 commented on a change in pull request #2769: HBASE-25032 Wait for region server to become online before adding it to online servers in Master

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caroliney14 commented on a change in pull request #2769:
URL: https://github.com/apache/hbase/pull/2769#discussion_r599168657



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File path: hbase-server/src/test/java/org/apache/hadoop/hbase/TestZooKeeper.java
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@@ -176,7 +176,7 @@ private void testSanity(final String testName) throws Exception {
   @Test
   public void testRegionAssignmentAfterMasterRecoveryDueToZKExpiry() throws Exception {
     MiniHBaseCluster cluster = TEST_UTIL.getHBaseCluster();
-    cluster.startRegionServer();
+    cluster.startRegionServerAndWait(2000);

Review comment:
       `startRegionServer` and `startRegionServerAndWait` do the same thing except the latter waits up to the passed in timeout to poll for the rs's online status in master (it will return early if it finds the rs is online before the timeout). the `startRegionServerAndWait` method gives the master a bit more time to get the updated `online` status from regionserver (which is updated after `HRegionServer.handleReportForDutyResponse` but only reported to master a while later, in `HRegionServer.tryRegionServerReport`). that's why master often needs an extra second to know the rs is alive, and if we try to proceed to do other tasks without this wait (such as assign regions), master will run into errors because it doesn't know the rs is alive yet. 




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