How to maintain bitmap index on a large table in DW?

Question

Hi all,
We have many tables which are constantly doing either FULL or INCREMENTAL loading.
And we have created many BITMAP indexes and several B*Tree index (caused by PRIMARY KEY or UNIQUE key constraints) on those tables.
So, what I want to know is, how to maintain those BITMAP (and B*Tree) indexes for different loading mode?
like, should I drop the index before the full load and re-create it after that?
and do nothing in INCREMENTAL loading? I am aware that it will take more time to load with indexes.
any links, books, articles or opinions would be highly appreciated.
Thanks

Answer 1

Just to reiterate, add to what Adam said. From Oracle Doc
http://download.oracle.com/docs/cd/E11882_01/server.112/e17120/indexes002.htm#CIHJIDJG
Unusable indexes
An unusable index is ignored by the optimizer and is not maintained by DML. One reason to make an index unusable is to improve bulk load performance. (Bulk loads go more quickly if the database does not need to maintain indexes when inserting rows.) Instead of dropping the index and later re-creating it, which requires you to recall the exact parameters of the CREATE INDEX statement, you can make the index unusable, and then rebuild it.
You can create an index in the unusable state, or you can mark an existing index or index partition unusable. In some cases the database may mark an index unusable, such as when a failure occurs while building the index. When one partition of a partitioned index is marked unusable, the other partitions of the index remain valid.
An unusable index or index partition must be rebuilt, or dropped and re-created, before it can be used. Truncating a table makes an unusable index valid.
Beginning with Oracle Database 11g Release 2, when you make an existing index unusable, its index segment is dropped.
The functionality of unusable indexes depends on the setting of the SKIP_UNUSABLE_INDEXES initialization parameter. When SKIP_UNUSABLE_INDEXES is TRUE (the default), then:
•DML statements against the table proceed, but unusable indexes are not maintained.
•DML statements terminate with an error if there are any unusable indexes that are used to enforce the UNIQUE constraint.
•For nonpartitioned indexes, the optimizer does not consider any unusable indexes when creating an access plan for SELECT statements. The only exception is when an index is explicitly specified with the INDEX() hint.
•For a partitioned index where one or more of the partitions are unusable, the optimizer does not consider the index if it cannot determine at query compilation time if any of the index partitions can be pruned. This is true for both partitioned and nonpartitioned tables. The only exception is when an index is explicitly specified with the INDEX() hint.
When SKIP_UNUSABLE_INDEXES is FALSE, then:
•If any unusable indexes or index partitions are present, any DML statements that would cause those indexes or index partitions to be updated are terminated with an error.
•For SELECT statements, if an unusable index or unusable index partition is present but the optimizer does not choose to use it for the access plan, the statement proceeds. However, if the optimizer does choose to use the unusable index or unusable index partition, the statement terminates with an error.
Incremental load really matters the volume and whether for new dats you just add new partitions or subpartitions . If my incremntal go all over place and/or if I am touching few thousand rows. Yes might want to keep the indexes valid and let Oracle maintain it. IF millions added or incremental data just added to new part/subpart . Keeping indexes unsable for those partitions/subpartitions and the rebuilding it later may yield better results.