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h1. Introduction

The Petals ESB "Shared Area", more generally called "Registry", is an internal component in charge of storing internal data. The Petals ESB "Shared Area" can be viewed as a database shared by all Petals ESB nodes of a given Petals [topology|Topology Configuration].

For example, before sending a message to a service provider, the Petals ESB "Router" will request the Petals ESB "Shared Area" for the right endpoint according to the information in the message (interface name and/or service name and/or endpoint name).

Data stored in the area are all data that must be shared by all Petals ESB containers:
* endpoint name,
* service name,
* interface name,
* topology.

{note}The implementation of Petals ESB "Shared Area" must be the same for all nodes of a domain.{note}

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{anchor:Implementations}

| the [Petals ESB Hazelcast Registry client] | Yes, for a *distributed* topology |

h1. Installation

A default implementation of the Petals ESB "Shared Area" is provided with the archive of Petals ESB. No extra installation is required.
To install another Petals Shared Area implementation, just put its JAR files in a sub-directory of {{$PETALS_HOME/lib/implementations/registry}}.

{anchor:Configuration}
h1. Configuration

h2. Configuration parameter

The Petals ESB "Shared Area" implementation selection process is:
# if an implementation is set in the [topology definition|Topology Configuration] ({{topology/domain/registry-implementation}}), it is used,
# otherwise, the implementation used is the one available in the Petals ESB classpath.

See the documentation of the [Petals ESB "Shared Area" implementations|#Implementations] for other configuration parameters.

h2. Logging configuration parameters

The Petals ESB "Shared Area" uses the following logger to trace its execution: {{Petals.Communication.SharedArea}}.

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Petals.Communication.SharedArea.level=FINE
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