Database Reference
In-Depth Information
in Hadoop, nor is it present on the compute nodes like a normal table would
be. It is instead created in the shell database up on the control node. You
can see this by looking at the
dsql query plan
commands executed by
PDW when we create an external table. In
Figure 10.8
, you can see the table
is indeed created and that the location specifies it as the control node.
Figure 10.8
Creating the external table on the control node
As you can see, it is simply a normal table. However, this table is used
only to hold statistics and metadata about the table. PDW does not allow
any user data to be persisted in the control node. This includes external
tables. The metadata includes all the properties we set at creation time of
the external table itself. PDW attaches these metadata attributes using the
sp_addextendedproperty
system stored procedure, as shown in
Figure
