Index Rebuild, the Need vs the Implications Support Note 989093.1 (Getting Better) March 5, 2014Posted by Richard Foote in Doc 122008.1, Doc 989093.1, Index Rebuild, Oracle Indexes, Oracle Myths.
Once upon a time, Oracle Support had a note called Script: Lists All Indexes that Benefit from a Rebuild (Doc ID 122008.1) which lets just say I didn’t view in a particularly positive light :) Mainly because it gave dubious advice which included that indexes should be rebuilt if:
- Deleted entries represent 20% or more of current entries
- The index depth is more than 4 levels
It then detailed a script that ran a Validate Structure across all indexes in the database that didn’t belong in either the SYS or SYSTEM schema.
This script basically read through and sequentially locked all tables (maybe multiple times) in the database in order to list indexes that might not actually need a rebuild while potentially missing out on some that do. I could write a script that achieved the same result with far less overheads. For example, SELECT index_name FROM DBA_INDEXES where index_name like ‘A%’ and owner not in (‘SYS’, ‘SYSTEM’) would achieve a very similar result :)
Thankfully, note 122008.1 was eventually removed from My Oracle Support (MOS) some time ago, interestingly soon after I discussed the ramifications of this script in my Oracle Index seminars :)
I recently stumbled upon another related note on MOS regarding index rebuilds, Index Rebuild, the Need vs the Implications (Doc ID 989093.1). Although not perfect (for example while it mentions ANALYZE INDEX VALIDATE STRUCTURE can now be performed online, doing so means that INDEX_STATS is not populated making it a little pointless in this context), it is a significant improvement on the previous note and certainly well worth a read for Oracle newbies.
It also references a script to investigate a b-tree index structure (Doc ID 989186.1) that doesn’t rely on the Validate Structure of an index, making it a far less problematic to use, while also keeping a useful history of index characteristics. Also worth checking out.