Interface Summary
Interface Description

CompositeNodeStoreMonitor

CompositeNodeStoreStatsMBean

Interface Summary
Interface	Description
CompositeNodeStoreMonitor
CompositeNodeStoreStatsMBean

Class Summary
Class	Description
CompositeCheckpointMBean
CompositeNodeStore	A `NodeStore` implementation that combines other `NodeStore` instances mounted under paths defined by `Mount`.
CompositeNodeStore.Builder
CompositeNodeStoreService
CompositeNodeStoreStats
CrossMountReferenceValidator
CrossMountReferenceValidatorProvider	`Validator` which detects references crossing the mount boundaries
InitialContentMigrator
ModifiedPathDiff
MountedNodeStore
MountInfoProviderService
NodeMap<T>
PrivateStoreValidatorProvider	`Validator` which detects change commits to the read only mounts.
StringCache	This class caches the path strings used in the CompositeNodeState to avoid keeping too many strings in the memory.

Package org.apache.jackrabbit.oak.composite Description

Composition support

This package contains support classes for implementing a composite persistence at the NodeStore level.

Design goals

Transparency of the composition setup. Neither the NodeStores nor the code using a composite NodeStore should be aware of the specific implementation being used.
Persistence-agnosticity. The composition support should be applicable to any conformant NodeStore implementation.
Negligible performance impact. Composition should not add a significat performance overhead.

Implementation

The main entry point is the CompositeNodeStore, which wraps one or more NodeStore instances. Also of interest are the CompositeNodeState and CompositeNodeBuilder.

These classes maintain internal mappings of the 'native' objects. For instance, if the composite NodeStore holds two MemoryNodeStore instances, then a call to NodeStore.getRoot() will return a composite NodeState backed by two MemoryNodeState instances. Similarly, a call to NodeState.builder() will return a composite NodeBuilder backed by two MemoryNodeState instances.

Using this approach allows us to always keep related NodeStore, NodeState and NodeBuilder instances isolated from other instances.

Open items

1. Brute-force support for oak:mount nodes.

The Mount.getPathFragmentName() method defines a name pattern that can be used by mounted stores to contribute to a patch which is not owned by them. For instance, a mount named apps which owns /libs,/apps can own another subtree anywhere in the repository given that a node named :oak-mount-apps is found.

The current implementation naively queries all stores whenever the child node list is prepared. This is obviously correct but may be slow. CompositionContext.getContributingStores(java.lang.String, java.util.function.Function)