Checking archive log files with the db2cklog tool

Checking your archive log files ensures that known good log files are available in case a rollforward recovery becomes necessary and that the recovery operation does not fail because of a problem with a log file. The information in this topic tells you how to check log files with the db2cklog tool, and what to do if a log file does fail validation.

Before you begin

You need to have read permission on the archive log files, so that the db2cklog tool can read the log files and perform its checks. Only log files that are closed, such as archive log files, can be validated successfully. If you run the tool on a log file that is still active, the tool cannot check that file accurately and you will receive a warning to let you know that the file is still active.

About this task

The db2cklog tool reads either single log files or a range of numbered log files and performs checks on the internal validity of the files. Log files that pass validation without any error messages or warnings are known good files and you can use them during a rollforward recovery operation. If an archive log file fails validation with an error message or if a warning is returned, then you must not use that log file during rollforward recovery. An archive log file that fails validation cannot be repaired and you should follow the response outlined in this task for what to do next.
Checking your archive log files is useful in the following scenarios:
  • Immediately before a rollforward operation is started: If it becomes necessary to perform a rollforward recovery operation, you can first run the db2cklog tool against all the archive log files that are required to perform the rollforward operation to ensure that the log files are valid. Running the db2cklog tool against the log files beforehand helps avoid a situation where a recovery operation fails partway through because of a problem with a log file, necessitating a follow-on recovery operation.
  • Every time a log file is closed and copied to the log archive directory: As part of your day-to-day operations, archive log files can be checked as an added precaution to make sure that known good log files are always available. With this preventive measure, you know right away whether you need to locate a copy of a log file or if a full database backup to establish a new recovery point is needed. This helps to reduce any delay in the event that a rollforward recovery becomes necessary.

Procedure

To check your archive log files, you issue the db2cklog command from the command line and include the log file or files you want checked. Note that you do not specify full log file names with the db2cklog command but only the numeric identifiers that are part of the log file names. The numeric identifier of the S0000001.LOG log file is 1, for example; to check that log file, you specify db2cklog 1. If the archive log files are not in the current directory, include the relative or absolute path to the log files with the optional ARCHLOGPATH parameter.

  1. If you want to check the validity of a single archive log file, you specify the numeric identifier of that log file as log-file-number1 with the command. For example, to check the validity of the S0000000.LOG log file in the /home/amytang/tests directory, you issue the command db2cklog 0 ARCHLOGPATH /home/amytang/tests.
  2. If you want to check the validity of a range of archive log files, you include the first and last numeric identifier of that range with the command (from log-file-number1 to log-file-number2). All log files in the range are checked, unless the upper end of the range specified with log-file-number2 is numerically lower than the beginning of the range (specified with log-file-number1). In that case, only log-file-number1 is checked. For example, to check the validity of the log files ranging from S0000000.LOG to S0000005.LOG in the /home/nrichers/tests directory, you issue the command db2cklog 0 TO 5 ARCHLOGPATH /home/nrichers/tests

Results

The db2cklog tool will return a return code of zero for any file that passes validation. If a range of numbered archive log files is specified, the db2cklog tool will read each file in sequence, perform its checks and issue a return code for each file. The tool stops at the first error it encounters, even if a range of log files was specified and there are additional files the tool has not yet checked. The DBT message that is returned when an error is found can provide you with some more information about why an archive log file failed validation, but you cannot fix an invalid log file. If you receive a DBT warning message that a log file might still be active but know for certain that the file is an archive log file, then you should treat the archive log file as invalid and follow the response for what to do next outlined in this task.

Examples

The following example shows the typical output of the db2cklog command as it parses a log file, in this case S0000002.LOG. This file passes validation with a return code of zero.
$ db2cklog 2                                                      
     ____________________________________________________________________

                      _____     D B 2 C K L O G     _____

                            Db2 Check Log File tool
                                 I    B    M


          The db2cklog tool is a utility can be used to test the integrity
        of an archive log file and to determine whether or not the log file
                  can be used in the rollforward database command.

      ____________________________________________________________________


________________________________________________________________________________



========================================================
"db2cklog": Processing log file header of "S0000002.LOG"

"db2cklog": Processing log pages of "S0000002.LOG" (total log pages: "316840")
            ==> page "1" ...
            ==> page "25001" ...
            ==> page "50001" ...
            ==> page "75001" ...
            ==> page "100001" ...
            ==> page "125001" ...
            ==> page "150001" ...
            ==> page "175001" ...
            ==> page "200001" ...
            ==> page "225001" ...
            ==> page "250001" ...
            ==> page "275001" ...
            ==> page "300001" ...

"db2cklog": Finished processing log file "S0000002.LOG". Return code: "0".
========================================================

What to do next

If an archive log file fails validation, your response depends on whether or not you have a copy of the log file that can pass validation by the db2cklog tool. If you are not sure whether you have a copy of the log file, check the setting for the logarchmeth2 configuration parameter, which determines whether your database server archives a secondary copy of each log file. If you are validating logs as they are being archive and log mirroring is also configured on your data server, you might still be able to locate a copy of the log file in the log mirror path, as your data server does not recycle log files immediately after archiving.

  • If you have a copy of the archive log file, use the db2cklog command against that copy. If the copy of the log file passes validation, replace the log file that cannot be read with the valid copy of the log file.
  • If you have only one copy of the archive log file and that copy cannot be validated, the log file is beyond repair and cannot be used for rollforward recovery purposes. In this case, you must make a full database backup as soon as possible to establish a new, more recent recovery point that does not depend on the unusable log file for rollforward recovery.