Apache9 commented on a change in pull request #3723:
URL: https://github.com/apache/hbase/pull/3723#discussion_r739842907
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File path:
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/LoadCandidateGenerator.java
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@@ -34,27 +35,51 @@ BalanceAction generate(BalancerClusterState cluster) {
private int pickLeastLoadedServer(final BalancerClusterState cluster, int
thisServer) {
Integer[] servers = cluster.serverIndicesSortedByRegionCount;
- int index = 0;
- while (servers[index] == null || servers[index] == thisServer) {
- index++;
- if (index == servers.length) {
- return -1;
+ int selectedIndex = -1;
+ double currentLargestRandom = -1;
+ for (int i = 0; i < servers.length; i++) {
+ if (servers[i] == null || servers[i] == thisServer) {
+ continue;
+ }
+ if (selectedIndex != -1
+ && cluster.getNumRegionsComparator().compare(servers[i],
servers[selectedIndex]) != 0) {
+ // Exhausted servers of the same region count
+ break;
+ }
+ // we don't know how many servers have the same region count, we will
randomly select one
Review comment:
Checked the code again, it seems not a typical Reservoir Sampling, it
just uses the simple solution in your linked article, where we just assign
every element a random number and choose the greatest one. I think we'd better
add more detailed comments here otherwise it will easily confuse later
developers.
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