Quota violation policies

If quotas are set for the amount of space each HBase tenant can fill on HDFS, then a coherent quota violation policy should be planned and implemented on the system.

When a quota violation policy is enabled, the table owner should not be allowed to remove the policy. The expectation is that the Master automatically removes the policy. However, the HBase superuser should still have permission.

Automatic removal of the quota violation policy after the violation is resolved can be accomplished via the same mechanisms that it was originally enforced. But the system should not immediately disable the violation policy when the violation is resolved.

The following describes quota violation policies that you might consider.

Disabling Tables

This is the “brute-force” policy, disabling any tables that violated the quota. This policy removes the risk that tables over quota affect your system. For most users, this is likely not a good choice as most sites want READ operations to still succeed.

One hypothetical situation when a disabling tables policy might be advisable is when there are multiple active clusters hosting the same data and, because of a quota violation, it is discovered that one copy of the data does not have all of the data it should have. By disabling tables, you can prevent further discrepancies until the administrator can correct the problem.

Rejecting All WRITE Operations, Bulk Imports, and Compactions

This policy rejects all WRITEs and bulk imports to the region which the quota applies. Compactions for this region are also disabled to prevent the system from using more space because of the temporary space demand of a compaction. The only resolution in this case is administrator intervention to increase the quota that is being exceeded.

Rejecting All WRITE Operations and Bulk Imports

This is the same as the previous policy, except that compactions are still allowed. This allows users to set or alter a TTL on table and then perform a compaction to reduce the total used space. Inherently, using this violation policy means that you let used space to slightly rise before it is ultimately reduced.

Allowing DELETE Operations But Rejecting WRITE Operations and Bulk Imports

This is another variation of the two previously listed policies. This policy allows users to run processes to delete data in the system. Like the previous policy, using this violation policy means that you let used space slightly rises before it is ultimately reduced. In this case, the deletions are propagated to disk and a compaction actually removes data previously stored on disk. TTL configuration and compactions can also be used to remove data.