HP 3000 Manuals HP 3000 Manuals
Managing Log Files
The DBA must manage the size, number, and location of ALLBASE/SQL log
files. This is done by performing the following tasks using a special
set of SQLUtil log management commands:
* Monitoring the log with SHOWLOG
* Adding log files with ADDLOG
* Storing log files with STORELOG
* Rescuing log files with RESCUELOG
* Purging log files with PURGELOG
* Restoring log files with RESTORELOG
* Moving log files with MOVELOG
Monitoring the Log with SHOWLOG
Use the SHOWLOG command to display the names of the individual log files
(single or dual) associated with a DBEnvironment, the archive mode of the
log, and the available file space remaining.
Displaying Files in the Log.
You can use the SHOWLOG command to display the log file directory either
dynamically or statically. The dynamic SHOWLOG is done if you respond Y
to the prompt
Connect? (y/n) (opt):
The default option is a dynamic SHOWLOG.
Normally, you should do a dynamic SHOWLOG so as to display the most
current information about available log space and about the backup status
of log files. You use the static SHOWLOG only when it is not possible to
connect to the DBEnvironment, as after a media failure.
Here is an example of a dynamic SHOWLOG:
>> showlog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word: Return
Connect? (y/n) (opt): y
Archive Mode: ON
Log Sequence Number Containing Most Recent Archive Checkpoint: 1
Current Log Sequence Number: 1
First Log Sequence Number Needed for Recovery: 1
Log Mode is: Single
Number of Free Blocks: 340
First Log Name: DBELOG1.SOMEGRP.SOMEACCT
First Log File Status: Useable
Log File Size: 250
Log Identifier Is: 1
Log Sequence Number: 1
Log Backup Status: Not Ready for Backup
First Log Name: DBELOG2.SOMEGRP.SOMEACCT
First Log File Status: Useable
Log File Size: 250
Log Identifier Is: 2
Log Sequence Number: 0
Log Backup Status: Not Ready for Backup
In this example, SHOWLOG displays the following information:
* Archive logging is on, and the log mode is single, meaning that
only one set of files is maintained.
* The archive checkpoint--the point at which the last STOREONLINE
command began storing the DBEnvironment--is in the file with log
sequence number 1.
* The current log file is DBELOG1, which has a log sequence number
of 1.
* If rollforward recovery should become necessary, it would have to
start at log sequence number 1. After subsequent STOREONLINE
commands, this sequence number will become larger.
* DBELOG1 and DBELOG2 combined still have a total of 340 free log
blocks (pages).
* DBELOG1 has not yet been backed up. It is not yet ready for
backup, since it is the current log file, that is, it is still
being written to.
* A second log file, DBELOG2, has been added to the DBEnvironment
with the ADDLOG command. This file has not been used, so it still
has log sequence number 0. It has also not been backed up, since
it does not contain any log records, and thus has never needed to
be backed up.
* Note that since the DBEnvironment is in single logging mode, both
files have only a First Log Name.
The following is an example of a dynamic SHOWLOG display for a
DBEnvironment running in nonarchive mode with dual logging:
>> showlog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word: Return
Connect? (y/n) (opt): y
Archive Mode: OFF
Log Sequence Number Containing Most Recent Archive Checkpoint: 0
Current Log Sequence Number: 1
First Log Sequence Number Needed for Recovery: 0
Log Mode is: Dual
Number of Free Block(s): 259
First Log Name: DBELOG1.SOMEGRP.SOMEACCT
First Log File Status: Useable
Second Log Name: DBELOG2.SOMEGRP.SOMEACCT
Second Log File Status: Useable
Log File Size: 300
Log Identifier Is: 1
Log Sequence Number: 1
Log Backup Status: Backup Is Not Required
In this example, the Log Sequence Number Containing Most Recent Archive
Checkpoint and the First Log Sequence Number Needed for Recovery are both
0, since archive logging is off.
Log File Status Types.
For a dynamic SHOWLOG, the types of backup status are as follows:
Not Ready for Backup This is the current file, which is not full
yet.
Ready for Backup The file is full, and the DBE is now using a
different file, so this one is ready to be
stored with STORELOG.
Backup is Done The file has already been backed up.
Backup is Not Required The log file does not need to be backed up if
the DBEnvironment is in nonarchive mode, or the
DBEnvironment is in archive mode and this log
file has never been used.
For a static SHOWLOG, the types of backup status are as follows:
Backup is Required The file has not been backed up yet.
Backup is Done The file has already been backed up.
Backup is Not Required The DBEnvironment is in nonarchive mode, so the
file does not need to be backed up.
Displaying Available File Space.
You can also use the dynamic SHOWLOG command to display the number of
free log blocks (pages) available for logging. In archive mode, SHOWLOG
does not tell how many pages are available in previously used log files
that have not already been backed up. Until the files are backed up,
these log pages are not free.
Using the CHECKPOINT command.
For nonarchive log files, a CHECKPOINT command tells you how many free
log file pages there are, and it frees log file pages held by completed
transactions. If long transactions tend to fill up the log file, you
should increase the log file size.
For archive log files, a CHECKPOINT command also tells you how many free
log file pages there are, and it frees log file pages in files that have
been stored. CHECKPOINT does not tell how many pages are available in
previously used log files that have not already been backed up.
Moreover, CHECKPOINT uses more system resources than SHOWLOG, which is
the preferred method for obtaining the number of free pages.
To free log file pages in archive mode, you must back up some of the log
files using STORELOG. After backup, these files become available for
reuse as soon as there are no active transactions in them. As the number
of free log pages approaches zero, you should add log files, or use
STORELOG to make a backup of any non-current log file, which then becomes
available for reuse.
Adding Log Files with ADDLOG
Using multiple log files gives you the greatest flexibility with logging.
In nonarchive mode, you can add a file when it is needed for unusually
large transactions, and you can recover easily from a LOG FULL condition
without having to shut the DBEnvironment down. In archive mode, you can
achieve continuous DBEnvironment availability by adding a group of log
files, then developing a schedule of DBEnvironment and log backup.
To expand the capacity of a nonarchive or archive log, use the ADDLOG
command, as in the following example:
>> addlog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word:
Enter Log File Name(s) Separated by a Blank? DBELOG2.SOMEGRP.SOMEACCT
New Log File Size? 250
Add Log File (y/n)? y
Log file `DBELOG2' was Added.
Log Identifier Is: 2
If you are using dual logging, enter two log file names separated by a
blank. No more than two names are accepted. The minimum size you can
specify for an added log file is 250 pages.
After you add the file to the DBEnvironment, it will be used when the
current log file runs out of space.
Storing Log Files with STORELOG
If you are using archive logging, you must use the STORELOG command to
create backups of each log file as it fills up. When a file's status
(shown in the dynamic SHOWLOG display) is Ready for Backup, you should
use the STORELOG command to store a copy of the log. One method of
indicating which file to store is by entering its Log Identifier. Here
is an example:
>> storelog
DBEnvironment Name: PartsDBE
Maintenance Word: Return
Log Identifier (opt): 2
To File name? Save1
Use Static Store (y/n)? n
Store Log File (y/n)? y
Log file 'lgn1' with Sequence Number 2 was stored.
The second method of initiating a log file backup is to issue a STORELOG
command and press Return when you see the prompt for a log identifier.
In this case, STORELOG will back up the file with the lowest possible
sequence number that has Ready for Backup status in the dynamic SHOWLOG
display. If the STORELOG operation succeeds, the file will be given the
new backup status Backup is Done.
A third method of initiating a log file backup is to issue a STORELOG
command and enter 0 for the log identifier. In this case, STORELOG will
back up all the files which are ready for backup, in the proper sequence
by log sequence number, prompting you for filenames as each file is
stored. Using this method, all log files can be stored on one tape.
Important! For each successful STORELOG, label the backup tape with the
log file name, sequence number, and the date and time of the
backup. The sequence number will let you restore and recover
log files in the correct order in the event that rollforward
recovery is needed.
Rescuing Log Files with RESCUELOG
At certain times, it is necessary to store a copy of a log file that is
not yet ready for backup with the STORELOG command. One such time is
immediately following a media failure. In this event, STORELOG does not
work, since it is impossible to CONNECT to the DBEnvironment. Use the
RESCUELOG command to store a copy of any log files not yet backed up at
the time of the media failure, as in the following:
>> rescuelog
Log File Name: DBELOG6
Size Of The Log File: 250
To File Name? save6
Rescue Log File (y/n)? y
Log File 'DBELOG6' with Sequence Number 12 Was Rescued.
If the DBECon file is intact, you can use the static SHOWLOG command
after a media failure to display the sequence numbers of files with a
status of Backup Required. Then you can store these files with
RESCUELOG.
Restoring Log Files with RESTORELOG
After a media failure, you prepare for rollforward recovery by restoring
the DBEnvironment and the log files. After using RESTORE to restore the
DBECon file and all DBEFiles, use the RESTORELOG command to restore each
individual log file. The Rename prompt lets you enter a new file name
for the log. Each file is restored initially with its original name;
then ALLBASE/SQL prompts for a new file name.
The easiest way to restore and apply log files is to use the RESTORELOG
and the RECOVERLOG commands one after another for each file, as in the
following example:
>> restorelog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word: Return
Input Device: TAPE
Local (y/n) (opt): y
Restore the Log File (y/n)? y
Log File 'lgn1' was Restored.
Rename 'lgn1' Log File To: log0001
Log File 'lgn1' was Renamed to 'log0001'.
>> recoverlog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word: Return
Next Log File To Recover: log0001
Recover Log File (y/n)? y
Log File Recovered.
Next Possible Log Sequence Number is 2.
When a log file has been applied to the DBEnvironment as a part of
rollforward recovery, it will be purged by ALLBASE/SQL when it no longer
contains active transactions. For that reason, if doing partial recovery
in which your current log files are undamaged, make sure that the names
given restored log files while using the RESTORELOG command do not
conflict with the names of existing log files. Otherwise your existing
log files could be purged as RECOVERLOG completes its work.
(In fact, partial rollforward recovery is best conducted in a group which
is separated from the one containing your DBEConFile, SYSTEM DBEFileSet,
and log files to avoid undesired interaction between files with duplicate
names.) Do not attempt to purge logs yourself during the rollforward
recovery process.
Purging Log Files with PURGELOG
The only way to purge an individual log file that is no longer needed is
with the PURGELOG command. Example:
>> purgelog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Maintenance Word:
Log Identifier: 2
Purge Log File (y/n)? y
Log file(s) Purged.
In the case of dual logging, this command purges both filenames
associated with the log identifier.
You can purge a log file that has been backed up, provided it contains no
active transactions. You can also purge a log file that has never been
used. You cannot use PURGELOG during the rollforward recovery process.
If you wish to purge the DBEnvironment and the entire log, use the
PURGEALL command. To purge the DBE alone, use the PURGEDBE command.
NOTE You should not remove log files with the MPE/iX PURGE command,
since this action is not recorded in the DBECon file. For the same
reasons, do not use the PURGEFILE command to remove a log file
under any circumstances.
Moving Log Files with MOVELOG
You can move a log file from one location to another with the SQLUtil
MOVELOG command. Example:
>> movelog
DBEnvironment Name: PARTSDBE.SOMEGRP.SOMEACCT
Current Log File Name: DBELog1.SomeGrp.SomeAcct
Current Device: DISC
New Device: 2
New Log File Name: DBELog1.OtherGrp.SomeAcct
File moved.
MOVELOG lets you place log files on a device that is separate from the
data and index files of the DBEnvironment. Note that when you move a log
file, you specify its file name; this means that you can place the
different members of a dual log sequence on separate volume sets if you
choose.