Question

I have a table that holds information about different events, for example

CREATE TABLE events (
    id int not null primary key, 
    event_date date, ...
) 

I realized that 90% of all queries access only today events; the older rows are stored for history and eventually moved to an archive table.
However, events table is still large, and I wonder if I can improve the performance by creating a materialized view that has something like WHERE event_date = trunc(sysdate) and maybe index on event_date ? Is it allowed at all?

Thanks

Answer 1

yes this is allowed see “primary key materialized view”:

Primary key materialized views may contain a subquery so that you can
create a subset of rows at the remote materialized view site

and “complex materialized view”

If you refresh rarely and want faster query performance, then use
Method A (complex materialized view).

If you refresh regularly and can sacrifice query performance, then use Method B (simple materialized view).

at http://download.oracle.com/docs/cd/B10500_01/server.920/a96567/repmview.htm

In your example chances are good IMHO that this is not a “complex materialized view”:

CREATE MATERIALIZED VIEW events_today REFRESH FAST AS
SELECT * FROM EVENT WHERE event_date = trunc(sysdate);

Just try it and see if Oracle accepts it with the REFRESH FAST clause.

EDIT – another option:

Depending on your DB Edition (Enterprise + Partitioning) and Version (11gR2) you could use a new Oracle feature called INTERVAL partitioning to define “daily partitions” within the existing table. This way most of your queries get alot faster without effectively duplicating the data – see http://www.oracle.com/technetwork/database/options/partitioning/twp-partitioning-11gr2-2009-09-130569.pdf