The Directory-based implementation is the default IndexManager implementation. It is highly configurable and allows separate configurations for the reader strategy, back ends, and directory providers. Refer Section 5.3, “Directory Configuration”, Section 5.4, “Worker Configuration” and Section 4.3.4, “Reader Strategy Configuration” for more details.

The NRTIndexManager is an extension of the default IndexManager and leverages the Lucene NRT (Near Real Time) feature for low latency index writes. However, it ignores configuration settings for alternative back ends other than lucene and acquires exclusive write locks on the Directory.

The IndexWriter does not flush every change to the disk to provide low latency. Queries can read the updated states from the unflushed index writer buffers. However, this means that if the IndexWriter is killed or the application crashes, updates can be lost so the indexes must be rebuilt.

The Near Real Time configuration is recommended for non-clustered websites with limited data due to the mentioned disadvantages and because a master node can be individually configured for improved performance as well.

Specify a fully qualified class name for the custom implementation to set up a customized IndexManager. Set up a no-argument constructor for the implementation as follows:

[default|<indexname>].indexmanager = my.corp.myapp.CustomIndexManager

The custom index manager implementation does not require the same components as the default implementations. For example, delegate to a remote indexing service which does not expose a Directory interface.