Question / Problem
What is the Tar Persistence Manager and how to configure it?
Answer / Resolution
Tar Persistence Manager
You can store CRX content in a Persistence Manager. By default, when you install CRX 1.4, the persistence manager saves the repository content to tar files.
The Tar Persistence Manager (Tar PM) is a disk-based persistence manager that uses the tar file format for storing content and is useful in situations where high performance of creating and modifying data is required (as the Tar format is append-only, so writes are very efficient).
Tar PM clustering lets CRX compensate for hardware and software failures by eliminating a single point of failure (one server) while using applications without changes. Unlike clustering storage based on a database server (also available in CRX), Tar PM clustering is based on networked file systems.
Tar PM versus a RDBMS-based PM
Both Tar PM and database-based PMs support transactions, any file system, and optimization at runtime or in batch mode. Although Tar PM is a new technology, it does have the following advantages over using an database based persistence manager:
- Tar files are append-only.
- Tar files can be backed up easily online.
- Tar is a standard file format, accessible via known tools, such as tar, WinZip, and so on.
- Tar is a platform-independent format.
- Low cost of ownership and license.
- Tar PM is specifically designed for JCR repositories.
- Tar PM is faster than RDBMS-based persistence managers for the JCR use case.
- The Tar PM takes advantage of the very simple key-value pair data structure of CRX.
Configuring the Tar PM
The configuration options are: