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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->set_rep_limit method.

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