Re: Re: force index range scan vs index full scan through hints?

Hi Chris,
Yes, this should be possible, but you need multiple scans, not one. Add the USE_CONCAT hint and a FIRST_ROWS_1 hint as well. Otherwise you might want to rewrite the query using union all instead of the OR clauses. Regards
Lothar
----Ursprüngliche Nachricht----
Von : cstephens16_at_gmail.com
Datum : 10/08/2018 - 14:50 (GMT)
An : Oracle-L_at_freelists.org
Betreff : Re: force index range scan vs index full scan through hints? forgot version info: 12.2 3-node RAC running on Centos 7. On Fri, Aug 10, 2018 at 7:49 AM Chris Stephens <cstephens16_at_gmail.com> wrote: Is there a way to tell Oracle to use an index range scan instead of an index full scan? We have a table that gets created on the fly and quickly accumulates 100's of millions of rows before statistics are collected. Never mind why the table has no statistics (it's a (longish) story). As the table accumulates data, another process hits it with a piece of SQL that has a variable number of predicates of the from "id between :id1 and :id2 OR id between :id2 and id3 OR...". We have an index to support that SQL. Oracle initially chooses to full scan that index instead of range scan it until statistics are collected. Full scan performance is unacceptable. Is there a way to force the index range scan version? We can't use baselines (another story). We've tried INDEX_RS and INDEX_RS_ASC after observing INDEX hint doesn't get us what we want since index is already being used. INDEX_RS and INDEX_RS_ASC aren't in official documentation so I'm not even sure they are valid hints. As I write this, it occurs to me that dynamic sampling might help here and will try that but that obviously comes with some overhead. Any other options? Thanks for any insight.
chris

--

http://www.freelists.org/webpage/oracle-l Received on Fri Aug 10 2018 - 15:00:05 CEST