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

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CHAPTER 13 ■ PARTITIONING
Some may look at that and say, “Wow, eight statements—that is a lot of typing,” and it’s
true that this sort of thing would be unreasonable if you had hundreds of partitions (or more).
Fortunately, it is very easy to script a solution, and the previous would become simply
ops$tkyte@ORA10GR1> begin
2 for x in ( select partition_name
3 from user_tab_partitions
4 where table_name = 'BIG_TABLE2' )
5 loop
6 execute immediate
7 'alter table big_table2 move partition ' ||
8 x.partition_name;
9 end loop;
10 end;
11 /
PL/SQL procedure successfully completed.
All of the information you need is there in the Oracle data dictionary, and most sites that
have implemented partitioning also have a series of stored procedures they use to make
managing large numbers of partitions easy. Additionally, many GUI tools such as Enterprise
Manager have the built-in capability to perform these operations as well, without your needing
to type in the individual commands.
Another factor to consider with regard to partitions and administration is the use of
“sliding windows” of data in data warehousing and archiving. In many cases, you need to
keep data online that spans the last N units of time. For example, say you need to keep the
last 12 months or the last 5 years online. Without partitions, this is generally a massive INSERT
followed by a massive DELETE. Lots of DML, and lots of redo and undo generated. Now with
partitions, you can simply do the following:
1. Load a separate table with the new months’ (or years’, or whatever) data.
2. Index the table fully. (These steps could even be done in another instance and transported
to this database.)
3. Attach this newly loaded and indexed table onto the end of the partitioned table using
a fast DDL command: ALTER TABLE EXCHANGE PARTITION.
4. Detach the oldest partition off the other end of the partitioned table.
So, you can now very easily support extremely large objects containing time-sensitive
information. The old data can easily be removed from the partitioned table and simply
dropped if you do not need it, or it can be archived off elsewhere. New data can be loaded into
a separate table, so as to not affect the partitioned table until the loading, indexing, and so on
is complete. We will take a look at a complete example of a sliding window later in this chapter.
In short, partitioning can make what would otherwise be daunting, or in some cases
unfeasible, operations as easy as they are in a small database.