Database Reference
In-Depth Information
This histogram points out that the first and last partitions have just half as many rows as the interior partitions.
The data is not very evenly distributed at all. We'll see the trend continue for six and seven hash partitions:
EODA@ORA12CR1> exec hash_proc( 6, :x );
PL/SQL procedure successfully completed.
PN CNT HG
-- ---------- ------------------------------
p1 6104 **************
p2 6175 ***************
p3 12420 ******************************
p4 12106 *****************************
p5 6040 **************
p6 6009 **************
6 rows selected.
EODA@ORA12CR1> exec hash_proc( 7, :x );
PL/SQL procedure successfully completed.
PN CNT HG
-- ---------- ------------------------------
p1 6105 ***************
p2 6176 ***************
p3 6161 ***************
p4 12106 ******************************
p5 6041 ***************
p6 6010 ***************
p7 6263 ***************
7 rows selected.
As soon as we get back to a number of hash partitions that is a power of two, we achieve the goal of even
distribution once again:
EODA@ORA12CR1> exec hash_proc( 8, :x );
PL/SQL procedure successfully completed.
PN CNT HG
-- ---------- ------------------------------
p1 6106 *****************************
p2 6178 *****************************
p3 6163 *****************************
p4 6019 ****************************
p5 6042 ****************************
p6 6010 ****************************
p7 6264 ******************************
p8 6089 *****************************
8 rows selected.
