Why does Vertica seem to use less Memory than required by the sizing tools in DX Netops Performance Management
DX Netops Performance Management/Vertica use resource pools that use a portion of total memory for operations.
DX Netops 20.2, CA Performance Management 3.7
Vertica will use up to 95% of memory, but resource pools can reserve a part for their pools, cutting down that 95%.
So if that pool is used for only one hour, it will still reserve the memory needed, but only use part or all of the reserved for that one hour.
DX Netops Performance Management uses 7-8 resource pools reserving different amounts of memory, and not all are active all the time.
These pools ensure that at the time it is needed, that the memory required is available for the operations to complete, and that the operations do not hinder other operations that also need to complete.
If it can't then you can have failures to complete those operations such as failing reports.