Oracle 12c – Issues with the HEATMAP Segment even if the heat map feature is not used

By William Sescu

When I don’t need I feature, I don’t turn it on, or do not use it because it reduces the possibility to run into issues. Most of the times this is true, however, during the preparation for an RMAN workshop, the RMAN list failure command showed me the following dictionary issue.

RMAN> list failure;

using target database control file instead of recovery catalog
Database Role: PRIMARY

List of Database Failures
=========================

Failure ID Priority Status    Time Detected        Summary
---------- -------- --------- -------------------- -------
2          CRITICAL OPEN      13-FEB-2017 10:12:26 SQL dictionary health check: seg$.type# 31 on object SEG$ failed

I thought first, that it might be related to some incorrect errors shown by the health check (DBMS_HM), because there used to be some issues with that tool. But even after applying the following patch, nothing changed and the error still appears.

19543595: INCORRECT HEALTHCHECK ERRORS FROM DBMS_HM – FALSE ERRORS ON TS$ , FILE$ OR USER

So I started a manual health check again to get some more details.

SQL> BEGIN
  2  DBMS_HM.RUN_CHECK (check_name => 'Dictionary Integrity Check',
  3  run_name => 'WilliamsDICTrun002',
  4  input_params => 'CHECK_MASK=ALL');
  5  END;
  6  /

PL/SQL procedure successfully completed.

SQL> SELECT DBMS_HM.GET_RUN_REPORT('WilliamsDICTrun002') from dual;

DBMS_HM.GET_RUN_REPORT('WILLIAMSDICTRUN002')
---------------------------------------------------------------------
Basic Run Information
 Run Name                     : WilliamsDICTrun002
 Run Id                       : 61
 Check Name                   : Dictionary Integrity Check
 Mode                         : MANUAL
 Status                       : COMPLETED
 Start Time                   : 2017-02-13 10:56:58.250100 +01:00
 End Time                     : 2017-02-13 10:56:58.689301 +01:00
 Error Encountered            : 0
 Source Incident Id           : 0
 Number of Incidents Created  : 0

Input Paramters for the Run
 TABLE_NAME=ALL_CORE_TABLES
 CHECK_MASK=ALL

Run Findings And Recommendations
 Finding
 Finding Name  : Dictionary Inconsistency
 Finding ID    : 62
 Type          : FAILURE
 Status        : OPEN
 Priority      : CRITICAL
 Message       : SQL dictionary health check: seg$.type# 31 on object SEG$
               failed
 Message       : Damaged rowid is AAAAAIAABAAAK+RAAc - description: Ts# 1
               File# 2 Block# 28032 is referenced

Now I do have the ROWID, the file number and the block number of the affecting object. Let’s see what it is.

SQL> select FILE#, BLOCK#, TYPE#, TS#, BLOCKS from seg$ where rowid='AAAAAIAABAAAK+RAAc';

     FILE#     BLOCK#      TYPE#        TS#     BLOCKS
---------- ---------- ---------- ---------- ----------
         2      28032         11          1       1024
		 

SQL> SELECT segment_name, segment_type, block_id, blocks
  2  FROM   dba_extents
  3  WHERE
  4  file_id = 2
  5  AND
  6  ( 28032 BETWEEN block_id AND ( block_id + blocks ) );

SEGMENT_NAME               SEGMENT_TYPE               BLOCK_ID     BLOCKS
-------------------------- ------------------------ ---------- ----------
HEATMAP                    SYSTEM STATISTICS             28032       1024

Really strange. It is related to the HEATMAP segment, but I am not using the heat map feature, or used it in the past.

SQL> show parameter heat

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
heat_map                             string      OFF

SQL> select name, DETECTED_USAGES from DBA_FEATURE_USAGE_STATISTICS where name like 'Heat%';

NAME                     DETECTED_USAGES
------------------------ ---------------
Heat Map                               0

But how can I get this fixed now? You could either ignore this issue, create a SR at Oracle, or you can drop the statistics segment, in case you are not using the heatmap feature.

In my case, I decided to the drop the statistics segment by issuing the following command. Dropping the statistics segment works by setting the underscore parameter “_drop_stat_segment” to 1.

SQL> select SEGMENT_NAME, SEGMENT_TYPE from dba_extents where SEGMENT_TYPE = 'SYSTEM STATISTICS';

SEGMENT_NAME               SEGMENT_TYPE
-------------------------- ------------------------
HEATMAP                    SYSTEM STATISTICS

SQL> ALTER SYSTEM SET "_drop_stat_segment"=1 scope=memory;

System altered.

SQL> select SEGMENT_NAME, SEGMENT_TYPE from dba_extents where SEGMENT_TYPE = 'SYSTEM STATISTICS';

no rows selected

The heat map table is gone now. Let’s run the dictionary check again.

SQL> BEGIN
  2  DBMS_HM.RUN_CHECK (check_name => 'Dictionary Integrity Check',
  3  run_name => 'WilliamsDICTrun003',
  4  input_params => 'CHECK_MASK=ALL');
  5  END;
  6  /

PL/SQL procedure successfully completed.

SQL> SELECT DBMS_HM.GET_RUN_REPORT('WilliamsDICTrun003') from dual;

DBMS_HM.GET_RUN_REPORT('WILLIAMSDICTRUN003')
---------------------------------------------------------------------
Basic Run Information
 Run Name                     : WilliamsDICTrun003
 Run Id                       : 81
 Check Name                   : Dictionary Integrity Check
 Mode                         : MANUAL
 Status                       : COMPLETED
 Start Time                   : 2017-02-13 11:17:15.190873 +01:00
 End Time                     : 2017-02-13 11:17:15.642501 +01:00
 Error Encountered            : 0
 Source Incident Id           : 0
 Number of Incidents Created  : 0

Input Paramters for the Run
 TABLE_NAME=ALL_CORE_TABLES
 CHECK_MASK=ALL

Run Findings And Recommendations


RMAN> list failure;

using target database control file instead of recovery catalog
Database Role: PRIMARY

no failures found that match specification

Looks much better now.

Conclusion

Even if you are not using some features, you can still have trouble with them. 🙂