Setting memory limits for fenced-mode UDxs

Vertica calls a fenced-mode UDx's implementation of Vertica::UDXFactory::getPerInstanceResources() to determine if there are enough free resources to run the query containing the UDx (see Informing Vertica of Resource Requirements). Since these reports are not generated by actual memory use, they can be inaccurate. Once started by Vertica, a UDx could allocate far more memory or file handles than it reported it needs.

The FencedUDxMemoryLimitMB configuration parameter lets you create an absolute memory limit for UDxs. Any attempt by a UDx to allocate more memory than this limit results in a bad_alloc exception. For more information on configuration parameters, see Configuration parameters. For an example of setting FencedUDxMemoryLimitMB, see How resource limits are enforced.