39.2 Introduction

Freeze represents a set of persistence services, as shown in Figure 39.1.

Figure 39.1. Layer diagram for Freeze persistence services.

The Freeze persistence services are described below:

• The Freeze evictor is a highly-scalable implementation of an Ice servant locator that provides automatic persistence and eviction of servants with only minimal application code.

• The Freeze map is a generic associative container. Code generators are provided that produce type-specific maps for Slice key and value types. Appli­cations interact with a Freeze map just like any other associative container, except the keys and values of a Freeze map are persistent.

As you will see from the examples in this chapter, integrating a Freeze map or evictor into your Ice application is quite straightforward: once you define your persistent data in Slice, Freeze manages the mundane details of persistence.

Freeze is implemented using Berkeley DB, a compact and high-performance embedded database. The Freeze map and evictor APIs insulate applications from the Berkeley DB API, but do not prevent applications from interacting directly with Berkeley DB if necessary.