We have a couple of tables that are quite large (~200million rows), and each night we do delete and inserts of about 500k rows.
And after each insert we do rebuild index on all indexes on the table.
A lot of our batch jobs then run against these tables.
But for a couple of days now, the CBO has started doing a weird behaviour. On queries it used to do FTS, it now uses indexes and vice versa. Some of the indexes are obviously not that good to use since we are experiencing exceptional bad performance.
What can have happened? Could the table gone bad? And the indexes then look good for the CBO?
Thanks in advance!