Persistence

PPS maintains its objects in memory while it's running.

It will, as required:

• save its objects to persistent storage, either on demand while it's running, or at shutdown
• restore its objects on startup, either immediately, or on first access (deferred loading)

The underlying persistent storage used by PPS relies on a reliable filesystem, such as:

• disk—Power-Safe filesystem
• NAND Flash—ETFS filesystem
• Nor Flash—FFS3 filesystem
• other—a customer-generated filesystem

When PPS starts up, it immediately builds the directory hierarchy from the encoded filenames on the persistent filesystem. It defers loading the objects in the directories until first access to one of the files. This access could be an open() call on a PPS object, or a readdir() call on the PPS directory.

On shutdown, PPS always saves any modified objects to a persistent filesystem. You can also force PPS to save an object at any time by calling fsync() on the object. When PPS saves to a persistent filesystem, it saves all objects to a single directory.