How dangerous is the vulnerability?

Any database user, who has “create session” privilege, which means, who can log into the database, can use the security hole to execute any OS command in the ownership of the oracle database owner. This means, that both denial of service as well as access to all data is exposed.

Which versions are affected?

Affected are database versions 10.2.0.4 (incl. 10.2.0.4.3 containing latest security patches as of January 2010) as well as 11g (incl. 11.2.0.1).

What can I do to close this security vulernability?

You can revoke privileges from PUBLIC:

revoke execute on dbms_java from PUBLIC;
revoke execute on dbms_java_test from PUBLIC;
revoke execute on “oracle/aurora/util/Wrapper” from PUBLIC;
grant execute on sys.dbms_jvm_exp_perms to IMP_FULL_DATABASE;
grant execute on sys.dbms_jvm_exp_perms to EXP_FULL_DATABASE;
revoke execute on sys.dbms_jvm_exp_perms from PUBLIC;

If you are using a third party vendor application, you should contact your vendor to check compatibility with revoked privileges or test before implementing in production.

The environment was:

• 2 Node Oracle Clusterware 11.1.0.7 Cluster on Linux x86_64 using latest Recommended Patches as of October 19th. (pre PSU 11.1.0.7.1)
• Clusterware installed as unix user crs
• ASM installed as unix user oracle

The ASM instances could be started with SQL*Plus without any problems, but if the ASM instances were started by means of clusterware using srvctl (either from root, crs or oracle) the  ASM instances would crash at diskgroup mount with:

ORA-07445: exception encountered: core dump  [sskgds_find_rtn_hdr()+1171]
[SIGBUS] [ADDR:0x2AACD701342C] [PC:0x25799DF]
[Non-existent physical address] []

Oracle Support identified this behaviour as Bug 6952915, for which there are patches for Linux x86, x86_64 and Solaris Sparc64.

Unfortunately, the customer decided to bounce the instance, so that there is no possibility for intensive diagnosis. However, ASH report shows that a dozen sessions either waited on Wait event “cursor: pin S” or were active (ON CPU) without any SQL_ID. An AWR Report showed:

Top 5 Timed Events                                         Avg %Total
~~~~~~~~~~~~~~~~~~                                        wait   Call
Event                                 Waits    Time (s)   (ms)   Time Wait Class
------------------------------ ------------ ----------- ------ ------ ----------
cursor: pin S                   140,036,615      24,833      0 ######      Other
CPU time                                             19          72.9
log file sync                         8,767           8      1   30.2     Commit
log file parallel write               9,039           8      1   29.9 System I/O
control file parallel write           1,269           5      4   20.2 System I/O

Oracle Support confirmed that this is Bug 6904068 High CPU usage when there are “cursor: pin S” waits. We have filed a backport request for it, as there is no patch for our platform available yet.

You can determine if this happens when you take a look at “lsnrctl serv” output from your rac nodes:

Service "S_APP" has 1 instance(s).
  Instance "MDDB1", status READY, has 2 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:0 refused:0 state:ready
         REMOTE SERVER
         (ADDRESS=(PROTOCOL=TCP)(HOST=ora-vm1.intra)(PORT=1521))

Instead of ora-vm1.intra, this should be ora-vm1-vip.intra.

Why should I care?

If you use the default configuration, then you are using the parameter “REMOTE_LISTENER” and therefore Server Side Connect Time Load Balancing. This means, that the listeners of all nodes receive load information from all instances of all nodes and they can redirect connections to the least loaded instance, even if the instance is on another node. But the connect string they then send back to the client contains the physical IP address instead of the virtual.

In case of node crashes or kernel panics, etc. the client has to wait for the TCP timeout until this is detected.

Solution

tnsnames.ora:

LISTENER_MDDB1 =
  (ADDRESS_LIST =
    (ADDRESS = (PROTOCOL = TCP)(HOST = ora-vm1-vip.intra)(PORT = 1521))
  )

LISTENER_MDDB2 =
  (ADDRESS_LIST =
    (ADDRESS = (PROTOCOL = TCP)(HOST = ora-vm2-vip.intra)(PORT = 1521))
  )

init.ora:
alter system set local_listener = 'LISTENER_MDDB1' sid='MDDB1';
alter system set local_listener = 'LISTENER_MDDB2' sid='MDDB2';

In addition, there is one single session which has wait event “kjbdrmcvtq lmon drm quiesce: ping completion” (on instance 1) and 1-3 sessions with wait event “gc remaster“. (on instance 2) The cur_obj# of the session waiting on “gc remaster” is pointing to the segment being remastered.

Does anybody have any experience with DRM problems with 10.2.0.4 on Linux Itanium?

I know that it is possible to deactive DRM, but usually it should be beneficial to have it enabled. I could not find any reports of performance impact during DRM operation on metalink. Support is involved but clueless so far.

Regards,
Martin

http://forums.oracle.com/forums/message.jspa?messageID=3447436#3447436

We could provide a reproducible testcase and it turned out to be bug 7014855. The bug is platform specific to Linux Itanium port and a patch is available.

There is a nice feature, called Index Monitoring which switches a flag if the index is used.

ALTER INDEX schema.index MONITORING USAGE;

Internally, a recursive SQL Statement is executed for every parsing of a SQL:

update object_usage set flags=flags+1 where obj#=:1 and bitand(flags, 1)=0

To check whether the index was used, you can query the view v$object_usage. Unfortunately, the view definition contains a where clause to list only indexes of the current schema.

where io.owner# = userenv(’SCHEMAID’)

Therefore, you can create a new view or just omit the limitation from the where clause:

create or replace view V$ALL_OBJECT_USAGE
(OWNER,
INDEX_NAME,
TABLE_NAME,
MONITORING,
USED,
START_MONITORING,
END_MONITORING)
as
select u.name, io.name, t.name,
decode(bitand(i.flags, 65536), 0, ‘NO’, ‘YES’),
decode(bitand(ou.flags, 1), 0, ‘NO’, ‘YES’),
ou.start_monitoring,
ou.end_monitoring
from sys.user$ u, sys.obj$ io, sys.obj$ t, sys.ind$ i, sys.object_usage ou
where i.obj# = ou.obj#
and io.obj# = ou.obj#
and t.obj# = i.bo#
and u.user# = io.owner#

However, what is less known is that the DBMS_STATS can in some cases manipulate these flags. The issue is tracked with “Bug 6798910 – DBMS_STATS or EXPLAIN PLAN trigger index usage monitoring”. If you are using 10.2.0.4 and you are gathering stats manually with “CASCADE=>TRUE”, then the monitoring flag is set to “YES”. Obviously, in this case you can not identify candidate indexes for removal.

The bug occurs if you add/remove redo log groups on a cluster database, which has some of it´s instances shut down.

More information about this Bug, which is tracked with Bug ID 6786022 can be found on MetaLink. There is a patch for 10.2.0.4 and Linux x86-64 available.

• 8k Blocksize

SQL> DROP TABLE t1_8k purge;
 
SQL> CREATE TABLESPACE DEMO8K datafile SIZE 128M blocksize 8192;
 
TABLESPACE created.
 
Elapsed: 00:00:07.35
 
SQL> CREATE TABLE mdecker.t1_8k
(n1 NUMBER,
 n2 NUMBER)
 TABLESPACE DEMO8K;
 
TABLE created.
 
Elapsed: 00:00:00.02
 
SQL> INSERT INTO t1_8k
SELECT TRUNC(dbms_random.VALUE(10000000,100000000)) n1,
           TO_NUMBER(NULL) AS n2
    FROM dual
CONNECT BY LEVEL <= 500000
/
 
 
500000 ROWS created.
 
Elapsed: 00:00:06.89
 
SQL> BEGIN dbms_stats.gather_table_stats(
        ownname => 'MDECKER',
        tabname => 'T1_8K',
        estimate_percent => 100);
END;
/
 
PL/SQL PROCEDURE successfully completed.
 
Elapsed: 00:00:02.13
 
SQL> SELECT num_rows,blocks FROM dba_tables WHERE table_name = 'T1_8K';
 
  NUM_ROWS     BLOCKS
---------- ----------
    500000        874
 
Elapsed: 00:00:00.15
SQL> UPDATE t1_8k SET n2 = n1;
 
500000 ROWS updated.
 
Elapsed: 00:01:09.04
SQL> COMMIT;

• 16k Blocksize

SQL> CREATE TABLESPACE DEMO16K datafile SIZE 128M blocksize 16384;
 
TABLESPACE created.
 
Elapsed: 00:00:14.75
 
SQL> CREATE TABLE mdecker.t1_16k
(n1 NUMBER,
 n2 NUMBER)
 TABLESPACE DEMO16K;
 
TABLE created.
 
Elapsed: 00:00:00.03
 
SQL> INSERT INTO t1_16k
SELECT TRUNC(dbms_random.VALUE(10000000,100000000)) n1,
           TO_NUMBER(NULL) AS n2
    FROM dual
CONNECT BY LEVEL <= 500000
/  
 
 
500000 ROWS created.
 
Elapsed: 00:00:05.51
SQL> BEGIN dbms_stats.gather_table_stats(
        ownname => 'MDECKER',
        tabname => 'T1_16K',
        estimate_percent => 100);
END;
/  
 
PL/SQL PROCEDURE successfully completed.
 
Elapsed: 00:00:01.78
SQL> SELECT num_rows,blocks FROM dba_tables WHERE table_name = 'T1_16K';
 
  NUM_ROWS     BLOCKS
---------- ----------
    500000        436
 
Elapsed: 00:00:00.07
 
SQL>  UPDATE t1_16k SET n2 = n1;
 
500000 ROWS updated.
 
Elapsed: 00:20:20.89

As you can see, the update statement for the 8k blocksize table took around 69 seconds whereas the same update for the table in the 16k tablespace took more than 20 minutes. When executing oradebug short_stack, you can see that for the 16k update, the stacktrace is similar for many executions. So, a lot of time is spent in the kernel functions ktspfsrch() and ktspscan_bmb().


SQL> oradebug setospid 23668
Oracle pid: 18, Unix process pid: 23668, image: oracle@ora-vm1.intra (TNS V1-V3)
SQL> oradebug short_stack
.....ktspfsrch()+559<-ktspscan_bmb()+315 .....
SQL> oradebug short_stack
.....ktspfsrch()+559<-ktspscan_bmb()+315 .....
SQL> oradebug short_stack
.....ktspfsrch()+559<-ktspscan_bmb()+315 .....


It is important to understand that the problem is not necessarily related to the blocksize, but to the PCTFREE value. More information about this topic can be found here:

http://structureddata.org/files/jl_test_case.html
http://structureddata.org/2008/09/08/understanding-performance/
http://www.oraclealchemist.com/oracle/hey-guys-does-size-matter/

]]> http://www.ora-solutions.net/web/2009/04/09/assm-problem-with-too-low-pctfree/feed/ 0 http://www.ora-solutions.net/web/2009/03/12/intelligent-aka-adaptive-cursor-sharing-problem/ http://www.ora-solutions.net/web/2009/03/12/intelligent-aka-adaptive-cursor-sharing-problem/#comments Thu, 12 Mar 2009 05:01:40 +0000 Martin http://www.ora-solutions.net/web/?p=586 Today, at the last day of Hotsos Symposium 2009 Ric van Dyke presented on “Intelligent (aka adaptive) Cursor Sharing”, a new feature of Oracle Database 11g. The feature was created to fix the shortcomings of bind peeking on columns with histograms. Tom Kyte presented a few years ago on this topic when he talked about the impact of the wheather on Oracle database performance.

During the very interesting presentation Ric presented with a demo how this feature works but also showed a nasty side effect. He tested it on a million row table with a column “object type”, which was skewed. He bound several different values to the object_type bind variable causing 2 different execution plans to be used for the same sql_id. The problem with it was that he ended up with dozens of child cursors showing V$SQL.IS_SHARABLE => N.

It was not known whether this is a bug or whether the whole concept is flawed. I searched on metalink and found the appropriate document:

Bug 6644714 – High number of child cursors with adaptive cursor sharing
This issue is fixed in

* 11.2 (Future Release)
* 11.1.0.7 (Server Patch Set)
Lots of child cursors may be produced with adaptive cursor sharing enabled,
sometimes with overlapping or same bind value selectivity ranges (in v$sql_cs_selectivity).
This problem shows as LOAD_OPTIMIZER_STATS=’Y’ for many of the cursors in V$SQL_SHARED_CURSOR.

– and –

Bug 7213010 – Adaptive cursor sharing generates lots of child cursors

This issue is fixed in

* 11.2 (Future Release)
* 11.1.0.7 (Server Patch Set)

Lots of child cursors may be produced for a query with bind variables
appearing in at least two simple relational predicates
(eg. col :b).

v$sql_cs_selectivity shows that there are multiple equivalent / overlapping
ranges for a single cursor. The number of ranges gets bigger and bigger
as the query is run more times.

I then tried to verify if the problem indeed is gone in 11.1.0.7 and found out, that it isn´t.

Here is my testcase:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434

SQL> @/tmp/setup.sql Connected. SQL> DROP TABLE tab1 purge;   TABLE dropped.   SQL> CREATE TABLE tab1 (a int, 2 b varchar2(20), 3 padding varchar2(200)) 4 tablespace USERS;   TABLE created.   SQL> SQL> DROP sequence myid;   Sequence dropped.   SQL> CREATE sequence myid cache 1000;   Sequence created.   SQL> SQL> begin 2 FOR i IN 1..100000 3 loop 4 INSERT INTO tab1 VALUES (myid.NEXTVAL, 5 'AAAAAAAAAA', 6 rpad('*',200,'*')); 7 end loop; 8 9 FOR i IN 1..1000 10 loop 11 INSERT INTO tab1 VALUES (myid.NEXTVAL, 12 'BBBBBBBBBB', 13 rpad('*',200,'*')); 14 end loop; 15 16 FOR i IN 1..1000 17 loop 18 INSERT INTO tab1 VALUES (myid.NEXTVAL, 19 'CCCCCCCCCC', 20 rpad('*',200,'*')); 21 end loop; 22 23 FOR i IN 1..100 24 loop 25 INSERT INTO tab1 VALUES (myid.NEXTVAL, 26 'DDDDDDDDDD', 27 rpad('*',200,'*')); 28 end loop; 29 30 FOR i IN 1..10 31 loop 32 INSERT INTO tab1 VALUES (myid.NEXTVAL, 33 'EEEEEEEEEE', 34 rpad('*',200,'*')); 35 end loop; 36 37 INSERT INTO tab1 VALUES (myid.NEXTVAL, 38 'FFFFFFFFFF', 39 rpad('*',200,'*')); 40 41 commit; 42 end; 43 /   PL/SQL procedure successfully completed.   SQL> SQL> CREATE INDEX tab1_idx1 ON tab1 (b);   INDEX created.   SQL> SQL> begin dbms_stats.gather_table_stats(ownname => 'MDECKER', 2 tabname => 'TAB1', 3 method_opt =>'FOR ALL COLUMNS SIZE 254', 4 cascade=> TRUE, 5 estimate_percent => 100, 6 no_invalidate => FALSE); 7 end; 8 /   PL/SQL procedure successfully completed.   SQL> SQL> SET LINES 300 SQL> col table_name format a10 SQL> col owner format a8 SQL> SELECT owner, table_name,num_rows, blocks, round((blocks*8192)/1024/1024) AS MB 2 FROM dba_tables WHERE table_name = 'TAB1' AND owner = 'MDECKER';   OWNER TABLE_NAME NUM_ROWS BLOCKS MB -------- ---------- ---------- ---------- ---------- MDECKER TAB1 102111 3268 26   SQL> SQL> prompt "Press Enter to continue" "Press Enter to continue" SQL> pause   SQL> SQL> /* SQL> OWNER TABLE_NAME NUM_ROWS BLOCKS MB SQL> -------- ---------- ---------- ---------- ---------- SQL> MDECKER TAB1 102111 3268 26 SQL> SQL> */ SQL> SQL> SQL> SQL> SELECT b , count(*) FROM mdecker.tab1 GROUP BY b ORDER BY 1 DESC;   B COUNT(*) -------------------- ---------- FFFFFFFFFF 1 EEEEEEEEEE 10 DDDDDDDDDD 100 CCCCCCCCCC 1000 BBBBBBBBBB 1000 AAAAAAAAAA 100000   6 rows selected.   SQL> SQL> /* SQL> B COUNT(*) SQL> -------------------- ---------- SQL> FFFFFFFFFF 1 SQL> EEEEEEEEEE 10 SQL> DDDDDDDDDD 100 SQL> CCCCCCCCCC 1000 SQL> BBBBBBBBBB 1000 SQL> AAAAAAAAAA 100000 SQL> SQL> 6 rows selected. SQL> SQL> */ SQL> SQL> prompt "Press Enter to continue" "Press Enter to continue" SQL> pause   SQL> SELECT num_buckets, histogram FROM dba_tab_col_statistics WHERE table_name = 'TAB1' AND column_name = 'B';   NUM_BUCKETS HISTOGRAM ----------- --------------- 6 FREQUENCY   SQL> SQL> /* SQL> NUM_BUCKETS HISTOGRAM SQL> ----------- --------------- SQL> 6 FREQUENCY SQL> */ SQL> SQL> SQL> SQL> SQL> SQL> SHOW user USER IS "MDECKER" SQL> @/tmp/sql1.txt SQL> SET LINES 300 SQL> SET echo ON SQL> SET pages 10000 SQL> col bind format a120 SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> SQL> variable myvar varchar2(20) SQL> exec :myvar := 'AAAAAAAAAA';   PL/SQL procedure successfully completed.   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 0 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 2211052296   -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 889 (100)| | |* 1 | TABLE ACCESS FULL| TAB1 | 100K| 20M| 889 (1)| 00:00:11 | --------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   1 - filter("B"=:MYVAR)     18 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0   SQL> SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> exec :myvar := 'BBBBBBBBBB';   PL/SQL procedure successfully completed.   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 0 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 2211052296   -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 889 (100)| | |* 1 | TABLE ACCESS FULL| TAB1 | 100K| 20M| 889 (1)| 00:00:11 | --------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   1 - filter("B"=:MYVAR)     18 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0   SQL> SQL> exec :myvar := 'CCCCCCCCCC';   PL/SQL procedure successfully completed.   SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 1 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 1918680838   ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 36 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| TAB1 | 1000 | 210K| 36 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | TAB1_IDX1 | 1000 | | 4 (0)| 00:00:01 | -----------------------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   2 - access("B"=:MYVAR)     19 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'CCCCCCCCCC', ANYDATA())) 1918680838 1   SQL> SQL> exec :myvar := 'DDDDDDDDDD';   PL/SQL procedure successfully completed.   SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 2 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 1918680838   ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 5 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| TAB1 | 100 | 21600 | 5 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | TAB1_IDX1 | 100 | | 1 (0)| 00:00:01 | -----------------------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   2 - access("B"=:MYVAR)     19 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'CCCCCCCCCC', ANYDATA())) 1918680838 1 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'DDDDDDDDDD', ANYDATA())) 1918680838 2   SQL> SQL> exec :myvar := 'EEEEEEEEEE';   PL/SQL procedure successfully completed.   SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 3 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 1918680838   ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 2 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| TAB1 | 10 | 2160 | 2 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | TAB1_IDX1 | 10 | | 1 (0)| 00:00:01 | -----------------------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   2 - access("B"=:MYVAR)     19 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'CCCCCCCCCC', ANYDATA())) 1918680838 1 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'DDDDDDDDDD', ANYDATA())) 1918680838 2 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'EEEEEEEEEE', ANYDATA())) 1918680838 3   SQL> SQL> exec :myvar := 'FFFFFFFFFF';   PL/SQL procedure successfully completed.   SQL> prompt "Press enter to run" "Press enter to run" SQL> pause   SQL> SET termout off SQL> SELECT * FROM TABLE(dbms_xplan.display_cursor());   PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------- SQL_ID fhtgpcv2m2j4s, child number 4 ------------------------------------- SELECT /* MD_TESTCASE */ * FROM tab1 WHERE b = :myvar   Plan hash value: 1918680838   ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 2 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| TAB1 | 1 | 216 | 2 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | TAB1_IDX1 | 1 | | 1 (0)| 00:00:01 | -----------------------------------------------------------------------------------------   Predicate Information (IDENTIFIED BY operation id): ---------------------------------------------------   2 - access("B"=:MYVAR)     19 rows selected.   SQL> SELECT sql_id, is_obsolete, is_bind_sensitive, is_bind_aware, is_shareable, dbms_sqltune.extract_binds(bind_data) bind, plan_hash_value, child_number FROM 2 v$sql WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ fhtgpcv2m2j4s N Y N Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'CCCCCCCCCC', ANYDATA())) 1918680838 1 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'DDDDDDDDDD', ANYDATA())) 1918680838 2 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'EEEEEEEEEE', ANYDATA())) 1918680838 3 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'FFFFFFFFFF', ANYDATA())) 1918680838 4

You can see that after parsing for bind CCCCCCCC, the execution plan changes from full table scan to index range scan. Moreover child cursor 1 is marked “is_bind_aware=Y”. When now bind DDDDDDDD is used, there is a new child (#2) and child 1 is set to is_sharable=N. After using bind EEEEEEEE, child #2 is set to sharable=N and a new child #3 is created. This repeats until there are 5 child cursors, 2 of which are set to is_sharable=Y. When the script is executed multiple times, there is even a sixth child cursor.

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SQL_ID I I I I BIND(NAME, POSITION, DUP_POSITION, DATATYPE, DATATYPE_STRING, CHARACTER_SID, PRECISION, SCALE, MAX_LENGTH, LAST_CAPTURED PLAN_HASH_VALUE CHILD_NUMBER EXECUTIONS ------------- - - - - ------------------------------------------------------------------------------------------------------------------------ --------------- ------------ ---------- fhtgpcv2m2j4s N Y N N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 0 2 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'CCCCCCCCCC', ANYDATA())) 1918680838 1 1 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'DDDDDDDDDD', ANYDATA())) 1918680838 2 1 fhtgpcv2m2j4s N Y Y N SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'EEEEEEEEEE', ANYDATA())) 1918680838 3 1 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'FFFFFFFFFF', ANYDATA())) 1918680838 4 16 fhtgpcv2m2j4s N Y Y Y SQL_BIND_SET(SQL_BIND(NULL, 1, NULL, 1, 'VARCHAR2(32)', 178, NULL, NULL, 32, '12-MAR-09', 'AAAAAAAAAA', ANYDATA())) 2211052296 5 3

I wondered why the cursors are not sharable and queried v$sql_shared_cursor:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

SQL> SELECT * FROM v$sql_shared_cursor WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID ADDRESS CHILD_AD CHILD_NUMBER U S O O S L F E B P I S T A B D L T R I I R L I O E M U T N F A I T D L D B P C S C P T M B M R O P M F L P L A F L R L H ------------- -------- -------- ------------ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - fhtgpcv2m2j4s 23F4E438 23F4DAB0 0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N Y N N N N N N fhtgpcv2m2j4s 23F4E438 23D924D8 1 N N N N N N N N N N N N N N N N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N fhtgpcv2m2j4s 23F4E438 23D7E888 2 N N N N N N N N N N N N N N N N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N fhtgpcv2m2j4s 23F4E438 23D6B8C8 3 N N N N N N N N N N N N N N N N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N fhtgpcv2m2j4s 23F4E438 23D574D8 4 N N N N N N N N N N N N N N N N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N fhtgpcv2m2j4s 23F4E438 23B983B0 5 N N N N N N N N N N N N N N N N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N   6 rows selected.   SQL> SELECT sql_id, address, child_number, LOAD_OPTIMIZER_STATS, row_level_sec_mismatch FROM v$sql_shared_cursor WHERE sql_id = 'fhtgpcv2m2j4s';   SQL_ID ADDRESS CHILD_NUMBER L R ------------- -------- ------------ - - fhtgpcv2m2j4s 245CE53C 0 Y N fhtgpcv2m2j4s 245CE53C 1 N Y fhtgpcv2m2j4s 245CE53C 2 N Y fhtgpcv2m2j4s 245CE53C 3 N Y fhtgpcv2m2j4s 245CE53C 4 N Y fhtgpcv2m2j4s 245CE53C 5 N Y   SQL> SELECT * FROM v$sql_cs_statistics WHERE sql_id = 'fhtgpcv2m2j4s';   ADDRESS HASH_VALUE SQL_ID CHILD_NUMBER BIND_SET_HASH_VALUE P EXECUTIONS ROWS_PROCESSED BUFFER_GETS CPU_TIME -------- ---------- ------------- ------------ ------------------- - ---------- -------------- ----------- ---------- 245CE53C 3308340376 fhtgpcv2m2j4s 5 3946114705 N 1 0 2 0 245CE53C 3308340376 fhtgpcv2m2j4s 5 2785428864 Y 1 0 2 0 245CE53C 3308340376 fhtgpcv2m2j4s 4 1680726256 Y 1 2 3 0 245CE53C 3308340376 fhtgpcv2m2j4s 3 1438126164 Y 1 20 5 0 245CE53C 3308340376 fhtgpcv2m2j4s 2 451655377 Y 1 200 21 0 245CE53C 3308340376 fhtgpcv2m2j4s 1 4078512309 Y 1 2000 169 0 245CE53C 3308340376 fhtgpcv2m2j4s 0 479772785 Y 1 100000 9823 0   7 rows selected.   SQL> SELECT * FROM v$sql_cs_selectivity WHERE sql_id = 'fhtgpcv2m2j4s';   ADDRESS HASH_VALUE SQL_ID CHILD_NUMBER PREDICATE RANGE_ID LOW HIGH -------- ---------- ------------- ------------ ---------------------------------------- ---------- ---------- ---------- 245CE53C 3308340376 fhtgpcv2m2j4s 5 =MYVAR 0 0.000004 0.010773 245CE53C 3308340376 fhtgpcv2m2j4s 4 =MYVAR 0 0.000009 0.010773 245CE53C 3308340376 fhtgpcv2m2j4s 3 =MYVAR 0 0.000088 0.010773 245CE53C 3308340376 fhtgpcv2m2j4s 2 =MYVAR 0 0.000881 0.010773 245CE53C 3308340376 fhtgpcv2m2j4s 1 =MYVAR 0 0.008814 0.010773

It is not clear, why the cursors are not shared and why this is expressed in the flag “row_level_sec_mismatch”. From these tests we can see that the number of child cursors is still quite high.

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