1. Advanced Diagnostics Revisited Julian Dyke Independent Consultant
UKOUG Conference 2014
juliandyke.com

2. WARNING
Much of the content of this presentation is undocumented and unsupported by Oracle
Check with Oracle support before using any of these features in a production environment

3. Agenda Trace Parameters Features and Hints Execution Plans Events
ORADEBUG
ALTER Statements

4. Trace

5. Trace V$DIAG_INFO Introduced in Oracle 11.1
Session-specific view reporting various diagnostic parameters
Column Name
Data Type
INST_ID
NUMBER
NAME
VARCHAR2(64)
VALUE
VARCHAR2(512)
CON_ID
Current trace file can be determined using:
SELECT value FROM v$diag_info WHERE name = 'Default Trace File';
VALUE
/u01/app/oracle/diag/rdbms/target/TARGET/trace/TARGET_ora_5556.trc

6. Trace TRACEFILE_IDENTIFIER Parameter
Introduced in Oracle 8.1.7
Appends specified suffix to trace file name
Subsequent trace is immediately written to new file
Can be updated unlimited number of times
For example if the current trace file name is:
/u01/app/oracle/diag/rdbms/target/TARGET/trace/TARGET_ora_5556_TEST.trc
If the TRACEFILE_IDENTIFIER is set to "TEST":
ALTER SESSION SET tracefile_identifier = 'TEST';
Subsequent trace will be written to:
/u01/app/oracle/diag/rdbms/target/TARGET/trace/TARGET_ora_5556_TEST.trc
TRACEFILE_IDENTIFIER can also be set using ORADEBUG:
ORADEBUG SETTRACEFILEID TEST

7. Trace DBMS_SYSTEM.KSDWRT Procedure
To write to trace files and/or alert log use:
DBMS_SYSTEM.KSDWRT ( DEST NUMBER, -- 1 = Trace File, 2 = Alert Log TST VARCHAR2 -- Message );
For example:
BEGIN DBMS_SYSTEM.KSDWRT (1, ‘Output to trace file’); DBMS_SYSTEM.KSDWRT (2, ‘Output to alert log’); END;

8. Trace DBMS_MONITOR - Overview
Introduced in Oracle 10.1
Package to enable/disable trace and statistics
Defined in $ORACLE_HOME/rdbms/admin/dbmsmntr.sql
Trace subroutines include:
SESSION_TRACE_ENABLE / DISABLE
DATABASE_TRACE_ENABLE / DISABLE
CLIENT_ID_TRACE_ENABLE / DISABLE
SERV_MOD_ACT_TRACE_ENABLE / DISABLE
Statistics subroutines include:
CLIENT_ID_STAT_ENABLE / DISABLE
SERV_MOD_ACT_STAT_ENABLE / DISABLE
Trace subroutines are equivalent to event level 8
Include wait events by default

9. Trace DBMS_MONITOR - PLAN_STAT column
In Oracle 11.1 and above the following subroutines include the PLAN_STAT column:
SESSION_TRACE_ENABLE
DATABASE_TRACE_ENABLE
CLIENT_ID_TRACE_ENABLE
SERV_MOD_ACT_TRACE_ENABLE
PLAN_STAT specifies the dump frequency for row source (STAT) statistics
Values can be:
NEVER
FIRST_EXECUTION (default)
ALL_EXECUTIONS
Useful when individual statement executions are affected by data cardinality / selectivity

10. Parameters

11. Parameters V$PARAMETER
V$PARAMETER includes supported parameters
Column Name
Data Type
NUM
NUMBER
NAME
VARCHAR2(80)
TYPE
VALUE
VARCHAR2(4000)
DISPLAY_VALUE
DEFAULT_VALUE
VARCHAR2(255)
ISDEFAULT
VARCHAR2(9)
ISSES_MODIFIABLE
VARCHAR2(5)
ISSYS_MODIFIABLE
ISPDB_MODIFIABLE
Column Name
Data Type
IS_INSTANCE_MODIFIABLE
VARCHAR2(5)
ISMODIFIED
VARCHAR2(10)
ISADJUSTED
ISDEPRECATED
ISBASIC
DESCRIPTION
VARCHAR2(256)
UPDATE_COMMENT
HASH
NUMBER
CON_ID
CON_ID - new in Oracle > Container ID
ISPDB_MODIFIABLE is also new in 12.1

12. Parameters V$PARAMETER
V$PARAMETER includes supported parameters
Based on X$KSPPI - includes all parameters
Version
Supported
Unsupported
Total
348
2403
2751
352
2562
2914
367
2984
3351
381
3597
3978
To set an unsupported parameter use double quotes around name e.g.:
ALTER SESSION SET "_serial_direct_read" = NEVER;
V$PARAMETER includes non-default values for unsupported parameters

13. Parameters Unsupported parameters
V$PARAMETER only reports non-default values for unsupported parameters
To dump values for all parameters
including default parameters for unsupported parameters:
SELECT i.ksppinm||';'||sv.ksppstvl FROM x$ksppi i, x$ksppsv sv WHERE i.indx = sv.indx ORDER BY i.ksppinm;

14. Parameters V$PARAMETER_VALID_VALUES
V$PARAMETER_VALID_VALUES - supported parameters
Based on X$KSPVLD_VALUES - all parameters
Column Name
Data Type
NUM
NUMBER
NAME
VARCHAR2(64)
ORDINAL
VALUE
VARCHAR2(255)
ISDEFAULT
CON_ID
Version
Supported
Unsupported
Total 73 91
164 75
112
187 78
124
202

15. Parameters V$PARAMETER_VALID_VALUES
For example:
SELECT value_kspvld_values AS "Value", isdefault_kspvld_values AS "Default" FROM x$kspvld_values WHERE name_kspvld_values = '_serial_direct_read' ORDER BY ordinal_kspvld_values;
Value
Default
ALWAYS
FALSE
AUTO
NEVER
TRUE

16. Features and Hints

17. Features and Hints V$SQL_FEATURE
Based on X$QKSFM
Includes features and fixes
Column Name
Data Type
SQL_FEATURE
VARCHAR2(64)
DESCRIPTION
PROPERTY
NUMBER
Fixes can be identified from DESCRIPTION column
WHERE description LIKE 'Fix%'
Individual fixes can be enabled and disabled. For example:
ALTER SESSION SET "_fix_control"=' :off';

18. Features and Hints V$SQL_FEATURE
Version counts are:
Version0
Feature
Fix
Total 94
654
748 98
846
944
110
885
996
115
1071
1186

19. Features and Hints V$SQL_FEATURE_HIERARCHY
V$SQL_FEATURE describes the relationships between features
The root feature is QKSFM_ALL
The following query prints the hierarchy in a nested format:
SELECT lpad ( ' ' , level * 2 ,' ' ) || sql_feature FROM v$sql_feature_hierarchy CONNECT BY PRIOR sql_feature = parent_id START WITH parent_id = 'QKSFM_ALL';
....
QKSFM_TRANSFORMATION QKSFM_CBQT QKSFM_CVM QKSFM_DIST_PLCMT QKSFM_JOINFAC QKSFM_JPPD QKSFM_PLACE_GROUP_BY QKSFM_PULL_PRED ....

20. Features and Hints V$SQL_HINT
Based on X$QKSHT
Currently no concept of unsupported hints
Column Name
Data Type
NAME
VARCHAR2(64)
SQL_FEATURE
CLASS
INVERSE
TARGET_LEVEL
NUMBER
PROPERTY
VERSION
VARCHAR2(25)
VERSION_OUTLINE
Version
# Hints
273
277
314
332
INVERSE column
Describes the opposite hint e.g.: PUSH_PRED and NO_PUSH_PRED

21. Features and Hints V$SQL_HINT
VERSION column
Describes version in which hint was introduced:
Version
# New Hints
8.0.0 14
8.1.0 50
8.1.5 18
8.1.6 4
8.1.7 2
9.0.0 26
9.2.0 13 42 35 3
Version
# New Hints 2 4 32 5 19 6 37 18

22. Execution Plans

23. Execution Plans DBMS_XPLAN - Overview
Introduced in Oracle 9.2
Enhanced in subsequent releases
Defined in $ORACLE_HOME/rdbms/admin/dbmsxpln.sql
Useful subroutines include
DISPLAY - display a plan from a PLAN_TABLE
DISPLAY_AWR - display a plan from the AWR
DISPLAY_CURSOR - display a plan from the library cache
DISPLAY_PLAN – returns plan as a CLOB
DISPLAY_SQLSET – displays a plan from a SQL tuning set
DISPLAY_SQLPLAN_BASELIN E – displays a plan from SQL baseline
For example to display execution plan for statement most recently executed by the current session:
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR);

24. Execution Plans DBMS_XPLAN - FORMAT Column
All DISPLAY subroutines include a FORMAT column which can be:
BASIC
Minimum information
Display operation ID, name and option
TYPICAL
Default.
Display operation ID, name and option, #rows, #bytes and optimizer cost.
Includes pruning, parallel and predicate information when applicable
ALL
Maximum information
As TYPICAL plus projection, alias and remote SQL if applicable
SERIAL
Same as TYPICAL except parallel information is not displayed even if statement executes in parallel

25. Execution Plans DBMS_XPLAN - FORMAT Column Options
FORMAT column options can be fine-tuned using the following keywords:
ROWS - number of rows estimated by optimizer
BYTES - number of bytes estimated by optimizer
COST - optimizer cost information
PARTITION - partition pruning information
PARALLEL - parallel execution information
PREDICATE - predicate section
PROJECTION - projection section
ALIAS - query block name / object alias
REMOTE - distributed query information
NOTE - note section
If keyword is prefixed by a minus sign then specified information is excluded
BASIC ROWS - displays basic information plus number of rows
ALL -PROJECTION -NOTE displays everything except the projection and note sections

26. Execution Plans DBMS_XPLAN - Additional Statistics
For DISPLAY_CURSOR and DISPLAY_SQLSET, additional data can be output using the following keywords:
IOSTATS – shows IO statistics for all executions of the cursor
MEMSTATS – displays memory management statistics including
execution mode of operator
how much memory was used
number of bytes spilled to disk
ALLSTATS – both IOSTATS and MEMSTATS
LAST – only report statistics for last execution of cursor
IOSTATS, ALLSTATS and LAST require basic plan statistics which are collected by
setting STATISTICS_LEVEL parameter to ALL
specifying GATHER_PLAN_STATISTICS hint
MEMSTATS requires PGA memory management to be enabled by:
setting PGA_AGGREGATE_TARGET to non-zero value

27. Execution Plans Operations and Options
AWR includes some interesting (static) views that describe execution plan operations and options available in the installed database version
DBA_HIST_PLAN_OPERATION_NAME
Contains a list of row source operations
DBA_HIST_PLAN_OPTION_NAME
Contains a list of row source options
DBA_HIST_TOPLEVELCALL_NAME
Contains a list of top level calls
Used in DBA_HIST_ACTIVE_SESS_HISTORY

28. Events

29. Event Levels
Event has additional levels in recent versions
Level
Description
Version 1
Trace includes SQL statement, response time, service time, execution statistics (#rows, #LIOs #PRs #PWs)
In 10.2 and below execution plan written to trace file when associated cursor is closed.
In 11.1 and above execution plan written to trace file after first execution of each cursor - plan_stat = 'first_execution'
All 4
As level 1 plus bind varables 8
As level 1 plus wait times 16
As level 1 plus execution plans for every execution plan_stat = 'all_executions'
11.1 and above 32
As level 1 without any execution plans
plan_stat = 'never' 64
As level 1 plus execution plans for any statement execution requiring more than 60 seconds of DB time
and above

30. Event Bind Variables
Event level 4 trace only captures the first bind variable in array
EXECUTE dbms_monitor.session_trace_enable (binds=>TRUE);
CREATE TABLE driver (key VARCHAR2(4), name VARCHAR2(30));
DECLARE TYPE driver_tab IS TABLE OF driver%ROWTYPE; d driver_tab := driver_tab (); BEGIN d.extend (6); d(1).key := 'LHAM'; d(1).name := 'Lewis Hamilton'; d(2).key := 'NROS'; d(2).name := 'Nico Rosberg'; d(3).key := 'SVET'; d(3).name := 'Sebastian Vettel'; d(4).key := 'FALO'; d(4).name := 'Fernando Alonso'; d(5).key := 'DRIC'; d(5).name := 'Daniel Ricciardo'; d(6).key := 'JBUT'; d(6).name := 'Jenson Button';
FORALL j IN INSERT INTO driver VALUES (d(j).key,d(j).name);
FORALL j IN INSERT INTO driver VALUES (d(j).key,d(j).name); END;

31. Event Bind Variables
Trace will only contain bind variable values for two rows:
BINDS # : Bind# value="LHAM" Bind# value="Lewis Hamilton"
...
BINDS # : Bind# value="FALO" Bind# value="Fernando Alonso"
Note this issue has consequences for load generation / simulation tools such as HammerDB and LoadRunner which base their input on trace.
Trace only includes first row of each array insert
Remaining rows are not traced

32. Event 10053 Optimizer Decisions
To trace optimizer decisions use enable event 10053:
Level
Description
Version 1
Print statistics and computations
All 2
Print computations only
Details are only written to trace when the statement is hard-parsed

33. Event 10053 DBMS_SQLDIAG Provides APIs to diagnose SQL statements.
Used by diagnostic modules:
SQL_TESTCASE
SQL_DIAGNOSTIC
Defined in $ORACLE_HOME/rdbms/admin/dbmsdiag.sql
Includes DUMP_TRACE procedure:
Dumps trace (optimizer or compiler) trace for a specific SQL statement
Does not execute SQL statement to generate trace
Compiler trace is a superset of optimizer trace
Includes kkf library calls
Query block decisions
Expressions

34. Event 10053 DBMS_SQLDIAG DUMP_TRACE procedure parameters are: Name
Description
p_sql_id
Child cursor SQL_ID
p_child_number
Child cursor number
p_component
"Optimizer" or "Compiler"
p_file_id
tracefile_identifier
For example:
dbms_sqldiag.dump_trace ( p_sql_id => '2y220pbrk573n', p_child_number => 0, p_component => 'Optimizer', p_file_id => 'OPTIMIZER' );
Note that P_FILE_ID sets TRACEFILE_IDENTIFIER, but does not reset it at end of call so subsequent trace file be written to the new file. Alternatively NULL can be specified (the default)

35. ORADEBUG

36. ORADEBUG Introduction
Undocumented debugging utility available
as a standalone utility on Unix (oradbx)
as a standalone utility on VMS (orambx)
within Server Manager (svrmgr)
within SQL*Plus (8.1.5 and above)
Requires SYSDBA privilege
Options vary for each release
To list available options use:
SQL> ORADEBUG HELP

37. ORADEBUG Process Specification
There are four ways of specifying a process in ORADEBUG:
Using current process:
SQL> ORADEBUG SETMYPID
Using Oracle PID (V$PROCESS.PID)
SQL> ORADEBUG SETORAPID <pid>
Using operating system PID (V$PROCESS.SPID)
SQL> ORADEBUG SETOSPID <spid>
Using the Oracle process name:
SQL> ORADEBUG SETORAPNAME <pname>
For example:
SQL> ORADEBUG SETORAPNAME PMON

38. ORADEBUG Useful Commands
To display the current trace file name use:
SQL> ORADEBUG TRACEFILE_NAME
To flush the current trace file use:
SQL> ORADEBUG FLUSH
To set the maximum size of the current trace file to UNLIMITED use:
SQL> ORADEBUG UNLIMIT
To set the TRACEFILE_IDENTIFER parameter:
SQL> ORADEBUG SETTRACEFILEID <suffix>
To dump the currently executing statement (SQL or PL/SQL)
SQL> ORADEBUG CURRENT_SQL

39. ORADEBUG Dumps Dumps vary for each release: To list available dumps:
SQL> ORADEBUG DUMPLIST
To perform an dump immediately use:
SQL> ORADEBUG DUMP <dump_name> <level> [address]
To perform a dump periodically use:
SQL> ORADEBUG PDUMP [interval=<interval>] [ndumps=<count> <dump_name> <level> [address]

40. ORADEBUG Process Statistics
To dump process statistics use ORADEBUG PROCSTAT. For example:
SQL> ORADEBUG SETORAPNAME PMON SQL> ORADEBUG PROCSTAT
----- Dump of Process Statistics User time used = 65 System time used = 30 Maximum resident set size = Integral shared text size = 0 Integral unshared data size = 0 Integral unshared stack size = 0 Page reclaims = 7480 Page faults = 7 Swaps = 0 Block input operations = 1472 Block output operations = 32 Socket messages sent = 0 Socket messages received = 0 Signals received = 0 Voluntary context switches = 2555 Involuntary context switches = 387

41. ORADEBUG Components ORADEBUG includes internal documentation for
Events
SQL> ORADEBUG DOC
Internal Documentation
EVENT Help on events (syntax, event list, ...)
COMPONENT [<comp_name>] List all components or describe <comp_name>
Components are arranged in nested hierarchies
Each component has a unique name
Do not need to specify parent(s) to uniquely identify component
Most component descriptions include the internal module name(s) e.g.:
SQL_Execution SQL Execution (qer, qes, kx, qee)
Parallel_Execution Parallel Execution (qerpx, qertq, kxfr, kxfx, kxfq, kxfp)

42. ORADEBUG Components Components are grouped into eight libraries:
Library
Description
ADVCMP
Advanced Compression
CLIENT
Client
DIAG
Diagnostics
GENERIC
Numeric Events
LIBCELL
Exadata Cells
ORANET
Networking
PLSQL
PL/SQL
RDBMS

43. ORADEBUG Components
For example given the extract below from ORADEBUG DOC COMPONENT:
Components in library RDBMS:
SQL_Compiler SQL Compiler ((null)) SQL_Parser SQL Parser (qcs) SQL_Semantic SQL Semantic Analysis (kkm) SQL_Optimizer SQL Optimizer ((null)) SQL_Transform SQL Transformation (kkq, vop, nso) SQL_MVRW SQL Materialized View Rewrite ((null)) SQL_Vmerge SQL View Merging (kkqvm) SQL_Virtual SQL Virtual Column (qksvc, kkfi) SQL_APA SQL Access Path Analysis (apa) SQL_Costing SQL Cost-based Analysis (kko, kke)
The following are all valid:
SQL> ORADEBUG DOC RDBMS SQL> ORADEBUG DOC SQL_Compiler SQL> ORADEBUG DOC SQL_Optimizer SQL> ORADEBUG DOC SQL_Transform SQL> ORADEBUG DOC SQL_Vmerge

44. ORADEBUG Events The full event syntax is described in ORADEBUG:
SQL> ORADEBUG DOC EVENT
<event_spec>::= '<event_id> [<event_scope>] [<event_filter_list>] [<event_parameters>] [<action_list>] [off]'
<event_id> ::= <event_name | number>[<target_parameters>]
<event_scope> ::= [<scope_name>: scope_parameters]
<event_filter> ::= {<filter_name>: filter_parameters}
<action> ::= <action_name>(action_parameters)
<*_parameters> ::= <parameter_name> = <value>[, ]

45. ORADEBUG Events
Each event specification is comprised of up to four parts:
Name
Scope
Filter
Action
Not all of the above are always required
Defaults apply for many permutations
More information is available in:
SQL> ORADEBUG DOC EVENT NAME
SQL> ORADEBUG DOC EVENT SCOPE
SQL> ORADEBUG DOC EVENT FILTER
SQL> ORADEBUG DOC EVENT ACTION

46. ORADEBUG Events - Name Event names are optional:
Can be specified for some libraries
For example for the RDBMS library:
Name
Description
alert_text
event for textual alerts
trace_recursive
force tracing of recursive SQL statements
clientid_overwrite
overwrite client_identifier in client_info
sql_monitor
force monitoring of SQL statements
sql_trace
sql trace
pmon_startup
startup of pmon process
background_startup
startup of background processes
db_open_begin
start of database open operation

47. ORADEBUG Events - Scope
Scope is the SQL scope for RDBMS events
Defined using SQL[ ]
Syntax is
[SQL: sql_id <string> ]
For example:
[SQL: 3s1yukp05bzg6]
Multiple SQL_IDs can be specified using | as a separator
[SQL: 3s1yukp05bzg6 | aca4xvmz0rzup]

48. ORADEBUG Events - Filter
Filters include:
Library
Filter
Description
DIAG
occurence
Fire events after specified number of occurrences
callstack
Fire events when specified function is on stack
tag
Fire events when specified tag is set
RDBMS
process
Fire events for specific process
pgadep
Fire when pgadep is within specified range
GENERIC
errarg
Fire events for specific error argument
Filters must be enclosed in curly brackets. For example pgadep below:
SQL> ALTER SESSION SET EVENTS
'sql_trace[SQL: 32cqz71gd8wy3] {pgadep: exactdepth 0}
plan_stat=all_executions,wait=true,bind=true';

49. ORADEBUG Events - Filter
pgadep is the PGA depth (dep=N) in trace file.
Can take the following values:
exactDepth
lessThan
greaterThan
For example:
{pgadep: exactdepth 0}
For normal statement execution
dep = 0 SQL statement execution
For PL/SQL execution
dep = 0 PL/SQL execution
dep = 1 SQL statement execution

50. ORADEBUG Events - Action
Actions exist for each library (except PLSQL)
For the RDBMS library most actions correspond to ORADEBUG DUMP commands from older versions including:
Dump Name
Description
PROCESSSTATE
Dump process state
SYSTEMSTATE
Dump system state
HEAPDUMP
Dump memory heap
GLOBAL_AREA
Dump fixed global area(s)
BUFFERS
Dump all buffers in buffer cache
SET_TSN_P1
Set tablespace # for buffer dump
BUFFER
Dump all buffers for specific DBA
LIBRARY_CACHE
Dump the library cache
CURSORDUMP
Dump session cursors

51. ORADEBUG Events - SQL_TRACE
SQL_TRACE is an synonym for event and can be set using:
ORADEBUG
ALTER SYSTEM
ALTER SESSION
The ORADEBUG syntax is:
SQL> ORADEBUG DOC EVENT NAME SQL_TRACE
sql_trace: event for sql trace
Usage
sql_trace wait < false | true >, bind < false | true >, plan_stat < never | first_execution | all_executions | adaptive >, level <ub4>
The default level is 1

52. ORADEBUG Events - SQL_TRACE
For example:
ORADEBUG EVENT SQL_TRACE
ORADEBUG EVENT SQL_TRACE BIND=TRUE
ORADEBUG EVENT SQL_TRACE BIND=TRUE,WAIT=TRUE
ORADEBUG EVENT SQL_TRACE OFF
ORADEBUG EVENT SQL_TRACE PLAN_STAT=ALL_EXECUTIONS
ORADEBUG EVENT SQL_TRACE LEVEL=4

53. ORADEBUG Events - Examples
Numeric events can be set using ORADEBUG. Default level is 1
ORADEBUG EVENT 10053
ORADEBUG EVENT LEVEL 1
ORADEBUG EVENT OFF
The original syntax still works in Oracle 11g/12c
ORADEBUG EVENT TRACE NAME CONTEXT FOREVER, LEVEL 1
ORADEBUG EVENT TRACE NAME CONTEXT OFF

54. ALTER Statements

55. ALTER Statements SQL_TRACE
In all versions SQL_TRACE can be enabled using ALTER SESSION/SYSTEM
Examples shown for ALTER SESSION:
SQL> ALTER SESSION SET SQL_TRACE=TRUE;
In Oracle 11.1 and above SQL_TRACE is an event:
SQL> ALTER SESSION SET EVENTS 'sql_trace wait=true';
SQL> ALTER SESSION SET EVENTS 'sql_trace bind=true';
SQL> ALTER SESSION SET EVENTS 'sql_trace bind=true, wait=true';
SQL> ALTER SESSION SET EVENTS 'sql_trace plan_stat=all_executions';

56. ALTER Statements Numeric Events
Numeric events can still be set using ALTER SESSION / ALTER SYSTEM
SQL> ALTER SESSION SET EVENTS '10235';
SQL> ALTER SESSION SET EVENTS '10235 level 1';
SQL> ALTER SESSION SET EVENTS '10235 off';
The original syntax still works in Oracle 11g/12c
SQL> ALTER SESSION SET EVENTS '10235 trace name context forever, level 1';
SQL> ALTER SESSION SET EVENTS '10235 trace name context off';

57. ALTER Statements SQL_TRACE - Filter
Trace can be restricted to a specific SQL ID by specifying a filter:
SQL> ALTER SESSION SET EVENTS 'sql_trace [sql: sql_id=3s1yukp05bzg6] bind=true, wait=true';
Multiple SQL IDs can be specified using the | symbol as a separator
SQL> ALTER SESSION SET EVENTS 'sql_trace [sql: sql_id=3s1yukp05bzg6|aca4xvmz0rzup] bind=true, wait=true';

58. ALTER Statements TRACE - Components
Trace can be restricted to a specific components e.g.
SQL> ALTER SESSION SET EVENTS 'trace[rdbms.SQL_Optimizer.*]';
The library name can optionally be omitted e.g.
SQL> ALTER SESSION SET EVENTS 'trace[SQL_Optimizer.*]';
Disable trace again using:
SQL> ALTER SESSION SET EVENTS 'trace[SQL_Optimizer.*] off';
Individual components can also be filtered e.g.:
SQL> ALTER SESSION SET EVENTS 'trace[SQL_Optimizer.*][sql:3bnxc7htmf2ad]';

59. ALTER Statements Flushing Caches
To flush the buffer cache use:
ALTER SYSTEM FLUSH BUFFER_CACHE;
The buffer cache must be flushed to disk before attempting to dump blocks using the ALTER SYSTEM DUMP command
To flush the shared pool (library cache) use:
ALTER SYSTEM FLUSH SHARED_POOL;
Pinned objects will not be flushed

60. ALTER Statements Block Dumps
To dump a database block in Oracle 8.0 or above:
ALTER SYSTEM DUMP DATAFILE <absolute_file_number> BLOCK <block_number>;
To dump a range of database blocks:
ALTER SYSTEM DUMP DATAFILE <absolute_file_number> BLOCK MIN <minimum_block_number> BLOCK MAX <maximum_block_number>;
To dump a block from a datafile in a closed database:
ALTER SYSTEM DUMP DATAFILE '<file_name>' BLOCK <block_number>;

61. ALTER Statements Block Dumps
In Oracle 12c ASSM bitmap blocks cannot be dumped by default
Block is considered to be encrypted
Work around is to set
ALTER SESSION SET "_sga_clear_dump" = TRUE;
X$KSPPI description for this parameter is:
Allow dumping encrypted blocks in clear for debugging
Acknowledgements to Jonathan Lewis and Riyaj Shamsudeen for the above

62. ALTER Statements Redo Log Dumps
To identify the current redo log use:
SELECT member FROM v$logfile WHERE group# = ( SELECT group# FROM v$log WHERE status = 'CURRENT' );
To dump the contents of a redo log use:
ALTER SYSTEM DUMP LOGFILE '<logfilename>';
Also works for archived log files

63. ALTER Statements Redo Log Dumps
Full syntax is:
ALTER SYSTEM DUMP LOGFILE 'FileName' SCN MIN MinimumSCN SCN MAX MaximumSCN TIME MIN MinimumTime TIME MAX MaximumTime LAYER Layer OPCODE Opcode DBA MIN FileNumber . BlockNumber DBA MAX FileNumber . BlockNumber RBA MIN LogFileSequenceNumber . BlockNumber RBA MAX LogFileSequenceNumber . BlockNumber;
See MOS Note for further details

64. Thank You For Your Interest
Please send any questions or comments to: