clarax commented on a change in pull request #3575:
URL: https://github.com/apache/hbase/pull/3575#discussion_r686554888
##########
File path:
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionReplicaCandidateGenerator.java
##########
@@ -39,42 +44,37 @@
* @param regionIndexToPrimaryIndex Cluster.regionsIndexToPrimaryIndex
* @return a regionIndex for the selected primary or -1 if there is no
co-locating
*/
- int selectCoHostedRegionPerGroup(int[] primariesOfRegionsPerGroup, int[]
regionsPerGroup,
- int[] regionIndexToPrimaryIndex) {
- int currentPrimary = -1;
- int currentPrimaryIndex = -1;
- int selectedPrimaryIndex = -1;
+ int selectCoHostedRegionPerGroup(HashMap<Integer, ArrayList<Integer>>
primariesOfRegionsPerGroup,
+ Collection<Integer> regionsPerGroup, int[] regionIndexToPrimaryIndex) {
+
double currentLargestRandom = -1;
- // primariesOfRegionsPerGroup is a sorted array. Since it contains the
primary region
- // ids for the regions hosted in server, a consecutive repetition means
that replicas
- // are co-hosted
- for (int j = 0; j <= primariesOfRegionsPerGroup.length; j++) {
- int primary = j < primariesOfRegionsPerGroup.length ?
primariesOfRegionsPerGroup[j] : -1;
- if (primary != currentPrimary) { // check for whether we see a new
primary
- int numReplicas = j - currentPrimaryIndex;
- if (numReplicas > 1) { // means consecutive primaries, indicating
co-location
- // decide to select this primary region id or not
- double currentRandom = ThreadLocalRandom.current().nextDouble();
- // we don't know how many region replicas are co-hosted, we will
randomly select one
- // using reservoir sampling
(http://gregable.com/2007/10/reservoir-sampling.html)
- if (currentRandom > currentLargestRandom) {
- selectedPrimaryIndex = currentPrimary;
- currentLargestRandom = currentRandom;
- }
+ Map.Entry<Integer, ArrayList<Integer>> selectedPrimaryIndexEntry = null;
+
+ // primariesOfRegionsPerGroup is a hashmap of count of primary index on a
server. a count > 1
+ // means that replicas are co-hosted
+ for(Map.Entry<Integer, ArrayList<Integer>> pair :
primariesOfRegionsPerGroup.entrySet()) {
+ if (pair.getValue().size() > 1) { // indicating co-location
+ // decide to select this primary region id or not
+ double currentRandom = ThreadLocalRandom.current().nextDouble();
+ // we don't know how many region replicas are co-hosted, we will
randomly select one
+ // using reservoir sampling
(http://gregable.com/2007/10/reservoir-sampling.html)
+ if (currentRandom > currentLargestRandom) {
+ selectedPrimaryIndexEntry = pair;
+ currentLargestRandom = currentRandom;
}
- currentPrimary = primary;
- currentPrimaryIndex = j;
}
}
- // we have found the primary id for the region to move. Now find the
actual regionIndex
- // with the given primary, prefer to move the secondary region.
- for (int regionIndex : regionsPerGroup) {
- if (selectedPrimaryIndex == regionIndexToPrimaryIndex[regionIndex]) {
+ if (selectedPrimaryIndexEntry == null) {
+ return -1;
+ }
+
+ // we have found the primary id and the set of regions for the region to
move.
+ // now to return one of the secondary
+ for (Integer regionIndex : selectedPrimaryIndexEntry.getValue()) {
Review comment:
we store the region indexes of all colocated replicas here so we don't
need to do O(n) look up on regionIndexToPrimaryIndex.
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