Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 13 ■ PARTITIONING 607
On many occasions, I’ve seen that the implementation team will see they have a large
table, say of 10 million rows. Now, 10 million sounds like an incredibly large number (and five
or ten years ago, it would have been, but time changes all things). The team decides to partition
the data. But in looking at the data, there are no logical attributes that make sense for
RANGE partitioning. There are no sensible attributes for that. Likewise, LIST partitioning doesn’t
make sense. Nothing pops out of this table as being the “right thing” to partition by. So, the
team opts for hash partitioning on the primary key, which just happens to be populated by an
Oracle sequence number. It looks perfect, it is unique and easy to hash, and many queries are
of the form SELECT * FROM T WHERE PRIMARY_KEY = :X.
But the problem is, there are many other queries against this object that are not of that
form. For illustrative purposes, assume the table in question is really the ALL_OBJECTS dictionary
view, and while internally many queries would be of the form WHERE OBJECT_ID = :X, the
end users frequently have these requests of the application as well:
• Show me the details of SCOTT’s EMP TABLE (WHERE OWNER = :O AND OBJECT_TYPE = :T ➥
AND OBJECT_NAME = :N).
• Show me all of the tables SCOTT owns (WHERE OWNER = :O AND OBJECT_TYPE = :T).
• Show me all of the objects SCOTT owns (WHERE OWNER = :O).
In support of those queries, you have an index on (OWNER,OBJECT_TYPE,OBJECT_NAME). But
you also read that “local indexes are more available,” and you would like to be more available
regarding your system, so you implement with them. You end up re-creating your table like
this, with 16 hash partitions:
ops$tkyte@ORA10G> create table t
2 ( OWNER, OBJECT_NAME, SUBOBJECT_NAME, OBJECT_ID, DATA_OBJECT_ID,
3 OBJECT_TYPE, CREATED, LAST_DDL_TIME, TIMESTAMP, STATUS,
4 TEMPORARY, GENERATED, SECONDARY )
5 partition by hash(object_id)
6 partitions 16
7 as
8 select * from all_objects;
Table created.
ops$tkyte@ORA10G> create index t_idx
2 on t(owner,object_type,object_name)
3 LOCAL
4 /
Index created.
ops$tkyte@ORA10G> begin
2 dbms_stats.gather_table_stats
3 ( user, 'T', cascade=>true);
4 end;
5 /
PL/SQL procedure successfully completed.