Chapter 5. Messages

Table of Contents

Data Messages
Initial Update
Administrative Messages

The different modules involved in the replication communicate by means of xmlBlaster messages. In some cases these are PtP messages and in some other cases they are Pub/Sub messages. Basically a message has a metadata part and a content. In the metadata part the relevant part is the Qos (Quality of Service) and more specifically the ClientProperties which contain attributes used internally by the replication.

The replication messages can be divided into two groups: such messages which transport data to be replicated, and such messages which are used for administrative purposes, for example to inform or control one or more modules. The first are refered to as Data Messages while the later as Administrative Messages.

Data Messages

Initial Update

On initial update several messages are sent from the master to the slave. These messages are always intercepted by the ReplManagerPlugin which delegates processing to the ReplSlave.

Initial Dump

These messages are only sent if the configuration is such that an export of the database is necessary. The content of these messages can either be xml (where the binary content has been base64-encoded) or in compressed binary format. Since these database dumps can be very large, they are sent chunkwise. The size of these chunks is configurable and per default 1 MB before compression. The message is persistent and published as a PtD (can be multiple destinations) high priority (9) message to the interessed sessions.

Table 5.1. Attributes of Initial Dump message

Attribute NameTypeDefaultComment
Stringnull Mandatory . It contains the sessionId of the slave which shall receive the data for this initial update.