While testing Oracle 22.214.171.124 (on Red Hat Enterprise Linux), I recently bumped up against a problem with stats collections using DEGREE > 1 that results in an ORA-600.
20:56:41 SQL> BEGIN DBMS_STATS.GATHER_TABLE_STATS('TR_OWNER','TR_POL', Estimate_Percent=>dbms_stats.AUTO_SAMPLE_SIZE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE AUTO',cascade=>FALSE, Degree=>dbms_stats.AUTO_DEGREE); END;
20:56:41 2 /
BEGIN DBMS_STATS.GATHER_TABLE_STATS('TR_OWNER','TR_POL', Estimate_Percent=>dbms_stats.AUTO_SAMPLE_SIZE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE AUTO',cascade=>FALSE, Degree=>dbms_stats.AUTO_DEGREE); END;
ERROR at line 1:
ORA-20011: Approximate NDV failed: ORA-12801: error signaled in parallel query
server P024, instance db100.srv.com:TRXTPLT2 (2)
ORA-00039: error during periodic action
ORA-00600: internal error code, arguments: , [0x2AE3C33489B8], , ,
, , , , , , , 
ORA-06512: at "SYS.DBMS_STATS", line 23112
ORA-06512: at "SYS.DBMS_STATS", line 23205
ORA-06512: at line 1
If I execute with an estimate_percent of anything other than auto_sample_size, the ORA-20011 goes away, but the ORA-600 remains. Interestingly enough, if I execute with Degree=>1, everything is fine.
After doing more research and finding that I could execute a stats collection on other objects without any problems, I narrowed down the problem to the existence of certain types of function-based indexes. In particular, if the table has an index that uses either a DECODE or a CASE expression or a user-defined function, the problem occurs. As long as the table doesn't have one of these, everything works fine.
The contact to Oracle Support in regard to this issue replied as follows:
It possible you're getting the problem described in Bug:11774077 which is closed as a duplicate of Bug:10013177. For more information please read Note:10013177.8. Functional index causes max decode group by sql to truncate values / can cause dump.
Please check if one of the workarounds will solve your problem:
- Set _replace_virtual_columns=false
- Set _disable_function_based_index=true
- Gathering table stats using degree 1.
Ouch! Turning off the use of virtual columns and function-based indexes is *not* an option. We rely quite heavily on them in our application. And, for the tables that have this problem, gathering stats without doing it in parallel (degree 1) is doable, but not desirable as we have a limited window of time to collect stats and have relied on being able to collect in parallel to reduce the total time it takes to complete the collections.
We're still researching other options or workarounds and pushing on Oracle Support for a fix for this problem, but are not making much progress on either front at this point.
I'll update again soon with more information as I have it.