Which of the following descriptions about the function of HMaster in HBase is correct? (Multiple choice)

Question

Options

• ARegion load balancing, Region splitting and Region allocation after splitting
• BResponsible for creating tables, modifying tables/deleting tables
• CResponsible for load balancing of RegionServer
• DRegion migration after RegionServer failure

• A
  100% (57)

Explanation

All four options correctly describe HMaster responsibilities because HMaster is the central coordinator of an HBase cluster, handling both cluster-level management and table-level metadata operations.

Why each option is correct:

• A - HMaster drives Region splitting (when a Region grows too large) and then allocates the resulting child Regions to RegionServers, while continuously balancing Region distribution across the cluster.
• B - All DDL operations (CREATE TABLE, ALTER TABLE, DROP TABLE) go through HMaster, which updates the schema metadata stored in the hbase:meta table and in ZooKeeper.
• C - HMaster monitors RegionServer load via ZooKeeper heartbeats and uses a load balancer (e.g., StochasticLoadBalancer) to move Regions off overloaded servers.
• D - When a RegionServer dies, HMaster detects the lost ZooKeeper session, reads the dead server's WAL to recover data, and reassigns its Regions to surviving RegionServers.

Since this is an all-of-the-above question with no wrong options, the key insight is that HMaster owns everything except the actual read/write data path - RegionServers handle client I/O directly, while HMaster handles all coordination, failover, and schema management.

Memory tip: Think of HMaster as the "manager who never touches the product" - it assigns work (Region allocation), reorganizes workloads (load balancing), handles crises (failover), and manages the org chart (DDL), but the RegionServers do the actual data serving.

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