Nodes and Node Processes

There are two types of HADB nodes:

• Active nodes that store data.

• Spare nodes that do not contain any data initially, but perform as active nodes if an active node becomes unavailable. Spare nodes are optional but useful for achieving higher availability.

Each node has a parent process and several child processses. The parent process, called the node supervisor (NSUP), is started by the management agent. It is responsible for creating the child processes and keeping them running.

The child processes are:

• Transaction server process (TRANS), that coordinates transactions on distributed nodes, and manages data storage.

• Relational algebra server process (RELALG) that coordinates and executes complex relational algebra queries such as sorts and and joins.

• SQL shared memory server process (SQLSHM) that maintains the SQL dictionary cache.

• SQL server process (SQLC), that receives client queries, compiles them into local HADB instructions, sends the instructions to TRANS, receives the results and conveys them to the client. Each node has one main SQL server and one sub-server for each client connection.

• Node manager server process (NOMAN) that management agents use to execute management commands issued by the hadbm management client.