Re: Creating unique index on huge table.

  • From: Mladen Gogala <gogala.mladen@xxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Fri, 23 Sep 2016 16:32:11 -0400

Good thing for the original poster is that he is creating the primary key index, so he doesn't need to compute statistics. Computing statistics is very expensive and it took significant part of the total time for your procedure.

On 09/22/2016 07:32 PM, Tim Gorman wrote:


Several years ago, I accidentally dropped a unique index on a 55TB table, which represented about 12TB of index. There are several on this list who know exactly the circumstances, and one person on this list who was the recipient of the tearful phone call I made when I realized what I had done. :)

High-level description of what worked to rebuild it...

 1. Run "create partitioned index ... unusable" to create the
    partitioned index with all partitions empty.
 2. Create a shell-script to run NN SQL*Plus processes simultaneously,
    where "NN" is a number of your choice, each process doing the
      * alter index <index-name> partition <partition-name> parallel
        <degree> nologging compute statistics

We ordered the SQL*Plus calls inside the shell-script so that the partitions for the most-recent partitions (i.e. the table was partitioned by a DATE column) were populated first, and then let the builds progress back in time. Depending on the application, you can be doing some or all of the normal activities on the table. Our assumption (which proved correct) was that all DML occurs against the newest partitions, so those were the partitions that needed to be made "usable" first.

This approach won't eliminate downtime or performance problems, but it will likely minimize them.

I hope this makes sense?



On 9/22/16 15:43, Vadim Keylis wrote:
I am working on adding replication using third party tool(dbvisit) to our databases.
I have couple 5T highly transactional partition tables. I need to add a partition unique index to these tables without causing any outage or incurring performance hit. Will greatly appreciate suggestions on the best approach to do it.

Thanks so much,

Mladen Gogala
Oracle DBA
Tel: (347) 321-1217

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