Parrallel query execution for UNION ALL Queries

Hi,

If I have a query such as:

SELECT * FROM (SELECT * FROM A) UNION ALL (SELECT * FROM B) WHERE
blah='food';

Assuming the table A and B both have the same attributes and the data
between the table is not partitioned in any special way, does Postgresql
execute WHERE blah="food" on both table simultaiously or what? If not, is
there a way to execute the query on both in parrallel then aggregate the
results?

To give some context, I have a very large amount of new data being loaded
each week. Currently I am partitioning the data into a new table every
month which is working great from a indexing standpoint. But I want to
parrallelize searches if possible to reduce the perofrmance loss of having
multiple tables.

Benjamin