Fixed Table x$ktfbue has not statistics

While playing around 12.1.0.2 db, I ran my usual script to check tablespace usage details and it took ~59 secs (Elapsed: 00:00:59.02), which was high.
Ran the sql using “gather_plan_statistics” hint and below lines in the execution plan were of interest –

|  34 |      HASH GROUP BY                     |                    |      1 |      6 |      3 |00:00:58.68 |     129K|  54801 |  1160K|  1160K|  758K (0)|
|  35 |       VIEW                             | DBA_FREE_SPACE     |      1 |  21019 |     13 |00:00:00.01 |     129K|  54801 |       |       |          |
|  36 |        JOIN FILTER USE                 | :BF0000            |      1 |        |     13 |00:00:00.01 |     129K|  54801 |       |       |          |
|  37 |         UNION-ALL                      |                    |      1 |        |     19 |00:00:00.01 |     129K|  54801 |       |       |          |
|  38 |          NESTED LOOPS                  |                    |      1 |      1 |      0 |00:00:00.01 |       7 |      0 |       |       |          |
|  39 |           NESTED LOOPS                 |                    |      1 |      1 |      0 |00:00:00.01 |       7 |      0 |       |       |          |
|* 40 |            INDEX FULL SCAN             | I_FILE2            |      1 |      4 |      4 |00:00:00.01 |       1 |      0 |       |       |          |
|* 41 |            TABLE ACCESS CLUSTER        | FET$               |      4 |      1 |      0 |00:00:00.01 |       6 |      0 |       |       |          |
|* 42 |             INDEX UNIQUE SCAN          | I_TS#              |      4 |      1 |      4 |00:00:00.01 |       2 |      0 |       |       |          |
|* 43 |           TABLE ACCESS CLUSTER         | TS$                |      0 |      1 |      0 |00:00:00.01 |       0 |      0 |       |       |          |
|* 44 |            INDEX UNIQUE SCAN           | I_TS#              |      0 |      1 |      0 |00:00:00.01 |       0 |      0 |       |       |          |
|  45 |          NESTED LOOPS                  |                    |      1 |     10 |     10 |00:00:00.01 |      25 |      0 |       |       |          |
|  46 |           NESTED LOOPS                 |                    |      1 |     10 |     10 |00:00:00.01 |      21 |      0 |       |       |          |
|* 47 |            TABLE ACCESS FULL           | TS$                |      1 |      4 |      4 |00:00:00.01 |       9 |      0 |       |       |          |
|* 48 |            FIXED TABLE FIXED INDEX     | X$KTFBFE (ind:1)   |      4 |      2 |     10 |00:00:00.01 |      12 |      0 |       |       |          |
|* 49 |           INDEX UNIQUE SCAN            | I_FILE2            |     10 |      1 |     10 |00:00:00.01 |       4 |      0 |       |       |          |
|  50 |          NESTED LOOPS                  |                    |      1 |  21007 |      9 |00:00:57.85 |     129K|  54801 |       |       |          |
|* 51 |           HASH JOIN                    |                    |      1 |      7 |      9 |00:00:00.01 |      13 |      0 |  1115K|  1115K|  471K (0)|
|  52 |            NESTED LOOPS                |                    |      1 |      7 |      9 |00:00:00.01 |      12 |      0 |       |       |          |
|  53 |             NESTED LOOPS               |                    |      1 |     32 |      9 |00:00:00.01 |      11 |      0 |       |       |          |
|* 54 |              TABLE ACCESS FULL         | TS$                |      1 |      4 |      4 |00:00:00.01 |       9 |      0 |       |       |          |
|* 55 |              INDEX RANGE SCAN          | RECYCLEBIN$_TS     |      4 |      8 |      9 |00:00:00.01 |       2 |      0 |       |       |          |
|  56 |             TABLE ACCESS BY INDEX ROWID| RECYCLEBIN$        |      9 |      2 |      9 |00:00:00.01 |       1 |      0 |       |       |          |
|* 57 |            INDEX FULL SCAN             | I_FILE2            |      1 |      4 |      4 |00:00:00.01 |       1 |      0 |       |       |          |
|* 58 |           FIXED TABLE FULL             | X$KTFBUE           |      9 |   3125 |      9 |00:00:58.67 |     129K|  54801 |       |       |          |
|  59 |          NESTED LOOPS                  |                    |      1 |      1 |      0 |00:00:00.01 |      21 |      0 |       |       |          |
|  60 |           NESTED LOOPS                 |                    |      1 |      1 |      0 |00:00:00.01 |      21 |      0 |       |       |          |

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)
   - this is an adaptive plan
   - 3 Sql Plan Directives used for this statement

The E-Rows for X$KTFBUE is 3125 whereas A-Rows 9. Checking the stats on the table

SYS@orcl:1> set serveroutput on
SYS@orcl:1>
SYS@orcl:1>
SYS@orcl:1> exec print_table('select * from dba_tab_statistics where  table_name=''X$KTFBUE'' ');
OWNER                         : SYS
TABLE_NAME                    : X$KTFBUE
PARTITION_NAME                :
PARTITION_POSITION            :
SUBPARTITION_NAME             :
SUBPARTITION_POSITION         :
OBJECT_TYPE                   : FIXED TABLE
NUM_ROWS                      :
BLOCKS                        :
EMPTY_BLOCKS                  :
AVG_SPACE                     :
CHAIN_CNT                     :
AVG_ROW_LEN                   :
AVG_SPACE_FREELIST_BLOCKS     :
NUM_FREELIST_BLOCKS           :
AVG_CACHED_BLOCKS             :
AVG_CACHE_HIT_RATIO           :
SAMPLE_SIZE                   :
LAST_ANALYZED                 :
GLOBAL_STATS                  :
USER_STATS                    :
STATTYPE_LOCKED               :
STALE_STATS                   :
SCOPE                         : SHARED
-----------------

Looking at the directive details shows missing details on “F(SYS.TS$) – F(SYS.UNDO$) – F(SYS.X$KTFBUE)”

SYS@orcl:1> exec  print_table('select * from DBA_SQL_PLAN_DIR_OBJECTS where owner=''SYS'' and object_name=''X$KTFBUE'' ');
DIRECTIVE_ID                  : 16383234857226438245
OWNER                         : SYS
OBJECT_NAME                   : X$KTFBUE
SUBOBJECT_NAME                :
OBJECT_TYPE                   : TABLE
NOTES                         : NONONOYES
-----------------

PL/SQL procedure successfully completed.

SYS@orcl:1> exec  print_table('select * from DBA_SQL_PLAN_DIRECTIVES where DIRECTIVE_ID=''16383234857226438245'' ');
DIRECTIVE_ID                  : 16383234857226438245
TYPE                          : DYNAMIC_SAMPLING
ENABLED                       : NO
STATE                         : USABLE
AUTO_DROP                     : YES
REASON                        : JOIN CARDINALITY MISESTIMATE
CREATED                       : 28-MAY-16 09.21.20.000000 PM
LAST_MODIFIED                 : 28-MAY-16 11.12.20.000000 PM
LAST_USED                     : 28-MAY-16 10.21.29.000000000 PM
NOTES                         : MISSING_STATSNO{F(SYS.TS$) - F(SYS.UNDO$) - F(SYS.X$KTFBUE)}
-----------------

PL/SQL procedure successfully completed.

Lets gather fixed object stats :-

SYS@orcl:1> exec DBMS_STATS.GATHER_FIXED_OBJECTS_STATS;

PL/SQL procedure successfully completed.

Elapsed: 00:02:47.92

Ran the script again and it still took the same time, so checked the stats on X$KTFBUE and its still missing

SYS@orcl:1> exec print_table('select * from dba_tab_statistics where  table_name=''X$KTFBUE'' ');
OWNER                         : SYS
TABLE_NAME                    : X$KTFBUE
PARTITION_NAME                :
PARTITION_POSITION            :
SUBPARTITION_NAME             :
SUBPARTITION_POSITION         :
OBJECT_TYPE                   : FIXED TABLE
NUM_ROWS                      :
BLOCKS                        :
EMPTY_BLOCKS                  :
AVG_SPACE                     :
CHAIN_CNT                     :
AVG_ROW_LEN                   :
AVG_SPACE_FREELIST_BLOCKS     :
NUM_FREELIST_BLOCKS           :
AVG_CACHED_BLOCKS             :
AVG_CACHE_HIT_RATIO           :
SAMPLE_SIZE                   :
LAST_ANALYZED                 :
GLOBAL_STATS                  :
USER_STATS                    :
STATTYPE_LOCKED               :
STALE_STATS                   :
SCOPE                         : SHARED
-----------------

PL/SQL procedure successfully completed.

Reviewed few documents

Query Against DBA_EXTENTS Performs Slowly After Upgrade to 11.2.0.3 (Doc ID 1453425.1)
Bug 5259025 – The fixed table x$ktfbue has no statistics (Doc ID 5259025.8)

Gathered the stats on fixed table x$ktfbue

SYS@orcl:1>  exec DBMS_STATS.GATHER_TABLE_STATS('SYS','X$KTFBUE');

PL/SQL procedure successfully completed.

Elapsed: 00:00:34.09
SYS@orcl:1> exec print_table('select * from dba_tab_statistics where  table_name=''X$KTFBUE'' ');
OWNER                         : SYS
TABLE_NAME                    : X$KTFBUE
PARTITION_NAME                :
PARTITION_POSITION            :
SUBPARTITION_NAME             :
SUBPARTITION_POSITION         :
OBJECT_TYPE                   : FIXED TABLE
NUM_ROWS                      : 9581
BLOCKS                        :
EMPTY_BLOCKS                  :
AVG_SPACE                     :
CHAIN_CNT                     :
AVG_ROW_LEN                   : 47
AVG_SPACE_FREELIST_BLOCKS     :
NUM_FREELIST_BLOCKS           :
AVG_CACHED_BLOCKS             :
AVG_CACHE_HIT_RATIO           :
SAMPLE_SIZE                   : 9581
LAST_ANALYZED                 : 28-may-2016 22:55:47
GLOBAL_STATS                  : YES
USER_STATS                    : NO
STATTYPE_LOCKED               :
STALE_STATS                   :
SCOPE                         : SHARED
-----------------

Re-ran the sql script and Elapsed: 00:00:00.41