An ancient mystery
Date: Thu, 20 Nov 2008 21:05:16 -0600
Oracle 126.96.36.199 database on Solaris 8 (soon to be upgraded to 10g) Rule-based Optimizer
A query which has run for years using an indexed access to a very large
table (maybe 100 million rows)
suddenly decides to use a full-table scan, shutting down a critical business process.
Then after several hours, it switches back to using the index. All concerned claim that nothing changed before or after.
Needless to say the business users are nervous. They think maybe the database grew beyond some limit.
Can anyone think of an explanation?