what is the difference between shared hint and prallel hint?

March 20, 2024

In the database, I have noticed a query running with shared hint.

    SELECT /*+ SHARED (8) */ ID from tab1

I execute the query plan to understand more about it , I notice px send qc which means parallel

-----------------------------------------------------------------------------------------
| Id | Operation                 | Name            | Rows     | Bytes     | Cost | Time |
-----------------------------------------------------------------------------------------
|  0 | SELECT STATEMENT          |                 | 58773659 | 235094636 | 7389 |      |
|  1 |   PX COORDINATOR          |                 |          |           |      |      |
|  2 |    PX SEND QC (RANDOM)    | :TQ10000        | 58773659 | 235094636 | 7389 |      |
|  3 |     PX BLOCK ITERATOR     |                 | 58773659 | 235094636 | 7389 |      |
|  4 |      INDEX FAST FULL SCAN | IDX_RTEST3      | 58773659 | 235094636 | 7389 |      |
-----------------------------------------------------------------------------------------

I have execute parallel hint and I have got the same results, then what is the different between shared and parallel hint?

 select /*+parallel(8) */ ID from tab1

>Solution :

There isn’t really a difference. Oracle-generated code sometimes uses shared, but as that isn’t documented you should probably stick to parallel in your own code.

See MoS document 2416478.1 for a bit more information – I can’t quote from that because it requires a support contract to view it.