Berkeley DB Reference Guide:
  Berkeley DB Replication

Bulk transfer

Sites in a replication group may be configured to use bulk transfer by calling the DB_ENV->rep_set_config method with the DB_REP_CONF_BULK flag. When configured for bulk transfer, sites will accumulate records in a buffer and transfer them to another site in a single network transfer. Configuring bulk transfer makes sense for master sites, of course. Additionally, applications using client-to-client synchronization may find it helpful to configure bulk transfer for client sites as well.

When a master is generating new log records, or any information request is made of a master, and bulk transfer has been configured, records will accumulate in a bulk buffer. The bulk buffer will be sent to the client if either the buffer is full or if a permanent record (for example, a transaction commit or checkpoint record) is queued for the client.

When a client is responding to another client's request for information, and bulk transfer has been configured, records will accumulate in a bulk buffer. The bulk buffer will be sent to the client when the buffer is full or when the client's request has been satisfied; no particular type of record will cause the buffer to be sent.

The size of the bulk buffer itself is internally determined and cannot be configured. However, the overall size of a transfer may be limited using the DB_ENV->rep_set_limit method.

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