Roby,
We wish to use Oracle 8i features like partitioning
and global and local indexes in our datawarehousing
project.
ans -> Partitioning is only available as an add on to Enterprise edition, so
make sure your licensed appropriately.
We have the following doubts regarding these:
1)Does usage of local index make inserts,updates and
deletes slower as compared to global index?
ans -> No, it appears to have no effect at all, but from a maintenance point of
view, wow!
2)When is the use of Bitmap index preferable over
local index? We have tried using bitmap index and the
performance is slower compared to local index. Any
document on the usage of such indexes would be
helpful.
ans -> Bitmaps can be local as well as global. BUT beware of any column where
the number of values therein is subject to change, mostly addition, this causes
the RDBMS to have to rebuild the bitmap which really makes a mess and can slam
into a bug or two. Also where there the cardinality (ratio of the number of
values to number of rows) is HIGH. The closer you get to 1 the less likely it's
a good candidate.
3) When can we use parallelism to accelerate the speed
of execution of the queries. How is the degree of
parallelism to be given determined?
ans -> Yes, best bet is parallelism should equal the number of partitions. But
Warning, setting parallelism greater than the number of processors you have can
cause severe performance degradation.
Dick Goulet
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