16.3 ORADEBUG utility

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ORADEBUG is a powerful utility and provides a wealth of information. However, this utility has very little documentation available. This utility comes in handy to step deep into the internal structures of Oracle and understand the actual problem. The wonderful benefit of using this utility is that the information gathered using this is useful when calling Oracle Support. The information puts the problem closer to resolution. For example, in Chapter 15 (Performance Tuning: Cluster) there was a discussion about getting details regarding the IPC configuration, and this utility was used.

The ORADEBUG utility is invoked from an SQL*Plus session by simply connecting to it and executing the specific ORADEBUG command. For example to get help on the various commands available through ORADEBUG:

                SQL> oradebug help HELP           [command]                 Describe one or all commands SETMYPID                                 Debug current process SETOSPID       <ospid>                   Set OS pid of process to debug SETORAPID      <orapid>                  Set Oracle pid of process to                  [’force’]                   debug DUMP           <dump_name> <lvl>         Invoke named dump                  [addr] DUMPSGA       [bytes]                    Dump fixed SGA DUMPLIST                                 Print a list of available                                            dumps EVENT         <text>                     Set trace event in process SESSION_EVENT <text>                     Set trace event in session DUMPVAR       <p|s|uga>                  Print/dump a fixed PGA/SGA/                  <name> [level]          UGA variable SETVAR        <p|s|uga> <name> <value>   Modify a fixed PGA/SGA/UGA                                            variable PEEK          <addr> <len> [level]       Print/Dump memory POKE          <addr> <len> <value>       Modify memory WAKEUP        <orapid>                   Wake up Oracle process SUSPEND                                  Suspend execution RESUME                                   Resume execution FLUSH                                    Flush pending writes to trace                                           file CLOSE_TRACE                              Close trace file TRACEFILE_NAME                           Get name of trace file LKDEBUG                                  Invoke global enqueue service                                           debugger NSDBX                                    Invoke CGS name-service                                           debugger -G           <Inst-List | def | all>     Parallel oradebug command prefix -R           <Inst-List | def | all>     Parallel oradebug prefix (return                                            output SETINST      <instance# .. | all>        Set instance list in double quotes SGATOFILE    <SGA dump dir>              Dump SGA to file; dirname in                                            double quotes DMPCOWSGA    <SGA dump dir>              Dump & map SGA as COW; dirname in                                            double quotes MAPCOWSGA    <SGA dump dir>              Map SGA as COW; dirname in double                                            quotes HANGANALYZE  [level]                     Analyze system hang FFBEGIN                                  Flash Freeze the Instance FFDEREGISTER                             FF deregister instance from                                            cluster FFTERMINST                               Call exit and terminate instance FFRESUMEINST                             Resume the flash frozen instance FFSTATUS                                 Flash freeze status of instance SKDSTTPCS    <ifname>                    Helps translate PCs to names                 <ofname> WATCH        <address> <len>             Watch a region of memory                 <self|exist|all|                 target> DELETE       <local|global|target>       Delete a watchpoint                watchpoint <id> SHOW         <local|global|target>       Show watchpoints                watchpoints CORE                                     Dump core without crashing                                            process IPC                                      Dump ipc information UNLIMIT                                  Unlimit the size of the trace file PROCSTAT                                 Dump process statistics CALL         <func> [arg1] ...           Invoke function with arguments                [argn]

A more detailed list of all the debuggable commands is listed in Appendix 1.

In Version 9i, Oracle has introduced a new feature where the database or instance can be placed in a freeze state. This feature is enabled from the ORADEBUG utility and is discussed in the next section.

16.3.1 Flash Freeze

A common dilemma faced by database administrators is whether to identify the cause of a failure or to ensure that normal service is restored as quickly as possible. By invoking Flash Freeze for example, the database administrator can place a freeze on the instance, take a diagnostic snapshot (as illustrated in the output below) of the entire system at the time of failure, quickly restart the database, and then make a diagnostic analysis offline.

The output below enables the flash freeze option using ffbegin,at which point the instance is placed in a freeze state. Once the instance is placed in a freeze state, the ALTER SESSION... command below will generate a dump file in the user dump destination directory. Subsequent to the generation of the dump file the instance is resumed using the ffresumeinst command.

SQL> oradebug ffbegin Statement processed. SQL> alter session set events 'immediate trace name   systemstate level 10'; Session altered. SQL> oradebug ffresumeinst Statement processed.

All activities performed through the ORADEBUG utility are recorded in the alert log file. In the case of the flash freeze command, the alert log records a considerable amount of activities where the various background and foreground processes are frozen. Subsequently the activation information is also listed when they are activated.

Other flash freeze related commands supported by the ORADEBUG utility are:

FFBEGIN              Flash Freeze the Instance FFDEREGISTER         FF deregister instance from cluster FFTERMINST           Call exit and terminate instance FFRESUMEINST         Resume the flash frozen instance FFSTATUS             Flash freeze status of instance

The output below is an extract from the alert.log file, illustrating the flash freeze activity:

... Wed Sep 25 01:57:45 2002 Issuing ORADEBUG FFBEGIN to: Unix process pid: 3429,   image: [e-mail] (PMON) Issuing ORADEBUG FFBEGIN to: Unix process pid: 3431,   image: [e-mail] (DIAG) Wed Sep 25 01:57:45 2002 Issuing ORADEBUG FFBEGIN to: Unix process pid: 3433,   image: [e-mail] (LMON) Wed Sep 25 01:57:45 2002 Unix process pid: 3429, image: oracle@ora-db1.   summerskyus.com (PMON) flash frozen ORADEBUG FFSTATUS: Flash Freeze is in effect All processes in instance are frozen Issuing ORADEBUG FFDEREGISTER to: Unix process pid: 3429,   image: [e-mail] (PMON) Issuing ORADEBUG FFDEREGISTER to: Unix process pid: 3431,   image: [e-mail] (DIAG) Wed Sep 25 01:58:06 2002 Unix process pid: 3472, image: oracle@ora-db1.   summerskyus.com (P004) deregistered Wed Sep 25 01:58:06 2002 Unix process pid: 3470, image: oracle@ora-db1.   summerskyus.com (P003) deregistered Wed Sep 25 01:58:06 2002 ORADEBUG FFSTATUS: Flash Freeze is in effect ORADEBUG FFSTATUS: Instance has been deregistered All processes in instance are frozen Wed Sep 25 01:58:28 2002 Issuing ORADEBUG FFRESUMEINST to: Unix process pid: 3429,   image: [e-mail] (PMON) Issuing ORADEBUG FFRESUMEINST to: Unix process pid: 3431,   image: [e-mail] (DIAG)

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