Informix Warehouse Accelerator: Continuous Acceleration during Data Refresh

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Icon: IWA Logo TruckThe
information provided applies to the Informix Server Version 11.70.xC4
and later.

To refresh the data in a data mart of the Informix Warehouse
Accelerator, the data mart must be loaded with a new set of the complete
data. This can be done by dropping the existing data mart, re-creating
it and then loading it with the new data. Alternatively, the data mart
can be disabled and loaded. While this saves the procedure of dropping
and re-creating the data mart, it still means that the data mart is not
available during the loading of the new data. And as normally this
loading phase is the step that takes the longest, renewing the data
always renders the data mart unavailable for considerable time.

Fortunately, with version 11.70.FC4 of the Informix Server, it is now
possible to achieve continuous availability of a data mart even during
the procedure of renewing the data. For this, a second data mart with
the same definition, but a different name, needs to be created and
loaded. While this new data mart is being loaded, the old data mart is
still available for query acceleration. As soon as loading of the new
data mart is complete, the new data mart will become active. From that
moment onwards it will be utilized for the acceleration of newly
arriving queries. This switch over to the new data mart happens
automatically in the optimizer of the Informix Server, where it is
decided, whether a query can be accelerated. As soon as the last query
utilizing the old data mart has completed, the old data mart can be
dropped manually.

With this method, queries can be continuously accelerated even while
new data is being loaded. It should be noted however, that this method
of data refresh requires the double of the memory space needed normally
for the data mart, though only for a short time. Therefore the size of
the shared memory available for the worker nodes may need to be adjusted
accordingly. Parameter WORKER_SHM in the accelerator's configuration
file "dwainst.conf" specifies the relevant memory resource.

Also see the
description
in the manual "IBM Informix Warehouse Accelerator Administration
Guide".


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