Methods and apparatus for managing data flow in a continuous data replication system having journaling

An article, comprising:

• a storage medium having stored thereon instructions that when executed by a machine result in the following:
• receiving a data transfer request from a first component at a transmitter module in a continuous data replication system having a production site and a backup site, the production site having a transmitter module and a transmitter credit mechanism, the transmitter module to transmit data over a network for replication in the backup site;
• detecting a high-load condition at the transmitter module;
• modifying a flow of credits from the transmitter credit mechanism to the first component to reduce or stop data flow to the transmitter module.

A data replication system, comprising:

• a first data site having a transmitter module to receive data transactions;
• a backup data site having a receiver module to receive the data transactions to be replicated and a distributor module to perform journaling of data from the receiver module,
• the system including a memory to store instructions to enable:
• (a) receiving write data transactions from the first data site to be backed up at the backup data site;
• (b) writing the write data to a first position in a do data stream;
• (c) writing metadata for the write data to a first position in a do metadata stream;
• (d) reading data from a second position in the do data stream;
• (e) reading metadata from a second position in the do metadata stream;
• (f) reading data to be overwritten from a logical unit in the backup storage site, where location and size of the data to be overwritten is determined from the do metadata stream;
• (g) writing the data to be overwritten to a first position in an undo data stream;
• (h) writing metadata for the data to be overwritten to an undo metadata stream;
• (i) writing the write data to the logical unit in the backup storage site;
• and
• managing a flow of credits between the transmitter module, the receiver module, and the distributor module to manage data flow in one or more of steps (a)-(i).