Principle:Heibaiying BigData Notes HBase Coprocessor Observer
| Knowledge Sources | |
|---|---|
| Domains | HBase, Server_Side_Logic, Distributed_Storage |
| Last Updated | 2026-02-10 10:30 GMT |
Overview
Server-side hook mechanism in HBase that allows custom logic to be injected before or after core operations (Get, Put, Delete, Scan) at the RegionServer level.
Description
HBase Coprocessors are a framework for running user-defined code on the RegionServer, analogous to triggers in relational databases. The Observer coprocessor type provides callback hooks (prePut, postPut, preGet, postGet, preDelete, etc.) that execute around standard HBase operations. By extending BaseRegionObserver and overriding specific hooks, developers can implement custom behaviors such as data validation, secondary indexing, append semantics, or access control without modifying client code. Observers are registered per-table via the table descriptor and execute within the RegionServer JVM, making them suitable for operations that require server-side atomicity and low latency.
Usage
Apply this principle when you need to inject custom logic into HBase data operations at the server side, such as enforcing data integrity rules, implementing append-on-write semantics, building secondary indexes, or triggering side effects on mutations. Prefer coprocessors over client-side logic when the behavior must be enforced regardless of which client performs the operation.
Theoretical Basis
HBase Observer coprocessors follow the Aspect-Oriented Programming pattern applied to distributed storage:
- Hook Registration: A coprocessor class extending BaseRegionObserver is packaged as a JAR and registered on a table via the table descriptor or HBase shell.
- Lifecycle: The RegionServer loads the coprocessor when the region opens and calls start(). It is unloaded when the region closes via stop().
- Interception: Before each core operation, the RegionServer calls the corresponding pre* hook. After the operation completes, it calls the post* hook.
- Mutation Modification: Within pre* hooks, the coprocessor can read current state from the region, modify the mutation object in-place, or bypass the operation entirely.
- Ordering: Multiple coprocessors execute in priority order (specified at registration time).
Pseudo-code Logic:
// Abstract observer pattern
class MyObserver extends BaseRegionObserver {
@Override
void prePut(context, put, walEdit, durability) {
// Read current value from region
Result current = context.getRegion().get(new Get(put.getRow()));
// Modify put based on current state
put.addColumn(family, qualifier, transform(current, put));
}
}