Helper Processes

Helper Processes
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Helper processes accelerate the rate at which an Update Process can apply an incoming replication stream to the database on a replicating instance.

The GT.M database engine performs best when multiple processes concurrently access the database, cooperating with one another to manage it. Therefore, it is possible for the tens, hundreds or thousands of application processes executing on an originating instance to outperform a replicating instance with only a single Update Process. Helper processes enable the update process to apply database updates faster and thereby keep up.

There are two types of helper processes:

Reader: Reader processes read the update records in the Receive Pool and attempt to pre-fetch database blocks into the global buffer pools, so they are more quickly available for the Update Process.
Writer: Writer processes help the Update Process by flushing database and journal records from shared memory (global and journal buffers) to the file system.

A certain number of each type of helper process maximizes throughput. As a practical matter, as long as the file system bandwidth on a replicating instance is equal to or greater than that of the originating instance providing its replication stream, there need be little concern about having too many helper processes.


There may be other reasons for a replicating instance to lag behind its originating instance during replication. Helper processes cannot improve situations such as the following: There is a bottleneck in the network between the originating and replicating instances--increase the network bandwidth or use compression. The hardware of the replicating instance is not as capable as that of the hardware on the originating instance--upgrade the hardware of the replicating instance.

There may be other reasons for a replicating instance to lag behind its originating instance during replication. Helper processes cannot improve situations such as the following:

There is a bottleneck in the network between the originating and replicating instances--increase the network bandwidth or use compression.
The hardware of the replicating instance is not as capable as that of the hardware on the originating instance--upgrade the hardware of the replicating instance.