Introducing AE environment variables
An AE is connected to the NPS by an SQL function registration. This registration can be a scalar, table, or aggregate function.
More than one function can be associated with a specific AE.
- To specify options to the AE Runtime System that apply to all application languages.
- To specify options that apply to a specific language.
- To specify custom options for a specific application.
A Netezza appliance installation consists of two machine types: a host and one or more S-Blades (or SPUs). For performance reasons, these two types of machines use slightly different versions of Linux with different compiler libraries. Therefore, when you write an AE, you must compile and link two versions of an executable: one for the host and one for the SPUs. The host and the SPUs share a common network file directory tree--the AE Export Directory Tree. For more information on the runtime system and the AE export directory tree, see Developer principles.
The concept of AE-ENVs is similar to that of operating system environment variables. These variables are key/value pairs that hold and transmit information. Some variable key names have a specific meaning to the AE runtime system. Variable names starting with "nz" are reserved by Netezza for this purpose. You can create user-defined AE-ENVs that the system passes on to the executable. The language-specific APIs all have a function to return the values of any AE-ENV.
The AE registration utility register_ae automatically sets a number of necessary environment variables. Some AE functionality is available only by directly setting AE-ENV using the register_ae --environment option. This option can also be used to override any variables set by register_ae. For more information, see AE environment variables and register_ae.
Defining duplicate environment variable key names at registration time produces an error. However, duplicate variable key names that are defined dynamically, by using SQL or by using AE-ENV include files, can override prior definitions. For more information, see Order of variable parsing.