Today my friend ask me a question about setting logsecond to -1. The
following sentences were copied from DB2 InforCenter:
"By setting logsecond to -1, you will have no limit on the size of the
unit of work or the number of concurrent units of work. However,
rollback (both at the savepoint level and at the unit of work level)
could be very slow due to the need to retrieve log files from the
archive. Crash recovery could also be very slow for the same reason. "
The question is how to understand "the same reason" in sentence "Crash
recovery could also be very slow for the same reason." Does "the same
reason" means "the need to retrieve log files from the archive"? I
think it it should be "the need to retrieve log files from active log
files" because crash recovery just need read information from active
log files, not archive log files. Is it right?
James
7  3932 
On Jan 31, 7:16 am, James <huyu...@gmail. comwrote:
Today my friend ask me a question about setting logsecond to -1. The
following sentences were copied from DB2 InforCenter:
"By setting logsecond to -1, you will have no limit on the size of the
unit of work or the number of concurrent units of work. However,
rollback (both at the savepoint level and at the unit of work level)
could be very slow due to the need to retrieve log files from the
archive. Crash recovery could also be very slow for the same reason. "
The question is how to understand "the same reason" in sentence "Crash
recovery could also be very slow for the same reason." Does "the same
reason" means "the need to retrieve log files from the archive"? I
think it it should be "the need to retrieve log files from active log
files" because crash recovery just need read information from active
log files, not archive log files. Is it right?
James
Hi James,
"the same reason" does mean "the need to retrieve log files from the
archive". logsecond = -1 implies infinite logging and to be able to
support that, some active log files may need to be archived (keeping
space free in the log path). Therefore, depending on the amount of
work done, how large the active log window is, etc. log files may need
to be retrieved during crash recovery.
Regards,
Kelly
I am a bit puzzled here as to log file behavior.
Why would the log files have to be retrieved from the archive under
these (or nay conditions). I thought that if log files were active,
they get copied to the archived, but they do not get replaced,
removed, deleted from the the log path until they are fully
archivable.
By this I mean all transactions in the file have been either rolled
back, committed and externalized, and also applied in DPROP if
applicable. Until then, the log file is deemed to be active and must
stay in the log path.
Therefore, I don,t see how it would have to be retrieved from the
archive, even if logsecond=1.
Am I off in left field, lost in log path or what ?????
Thanls, Pierre.
On 31 jan, 14:39, kschl...@ca.ibm .com wrote:
On Jan 31, 7:16 am, James <huyu...@gmail. comwrote:
Today my friend ask me a question about settinglogsecon dto -1. The
following sentences were copied from DB2 InforCenter:
"By settinglogsecon dto -1, you will have no limit on the size of the
unit of work or the number of concurrent units of work. However,
rollback (both at the savepoint level and at the unit of work level)
could be very slow due to the need to retrieve log files from the
archive. Crash recovery could also be very slow for the same reason. "
The question is how to understand "the same reason" in sentence "Crash
recovery could also be very slow for the same reason." Does "the same
reason" means "the need to retrieve log files from the archive"? I
think it it should be "the need to retrieve log files from active log
files" because crash recovery just need read information from active
log files, not archive log files. Is it right?
James
Hi James,
"the same reason" does mean "the need to retrieve log files from the
archive". *logsecond= -1 implies infinite logging and to be able to
support that, some active log files may need to be archived (keeping
space free in the log path). *Therefore, depending on the amount of
work done, how large the active log window is, etc. log files may need
to be retrieved during crash recovery.
Regards,
Kelly
>"Pierre StJ" <p.*********@vi deotron.cawrote in message
>I am a bit puzzled here as to log file behavior.
Why would the log files have to be retrieved from the archive under
these (or nay conditions). I thought that if log files were active,
they get copied to the archived, but they do not get replaced,
removed, deleted from the the log path until they are fully
archivable.
By this I mean all transactions in the file have been either rolled
back, committed and externalized, and also applied in DPROP if
applicable. Until then, the log file is deemed to be active and must
stay in the log path.
Therefore, I don,t see how it would have to be retrieved from the
archive, even if logsecond=1.
Am I off in left field, lost in log path or what ?????
Thanls, Pierre.
If the number of log files (primary + secondary) is specified, then there
cannot be an active transaction in the archive log. If the number is set
to -1, that means there is no limit and active transactions may spill over
to the archive log.
Pierre StJ wrote:
On 31 jan, 14:39, kschl...@ca.ibm .com wrote:
>On Jan 31, 7:16 am, James <huyu...@gmail. comwrote:
>>Today my friend ask me a question about settinglogsecon dto -1. The
following sentences were copied from DB2 InforCenter:
"By settinglogsecon dto -1, you will have no limit on the size of the
unit of work or the number of concurrent units of work. However,
rollback (both at the savepoint level and at the unit of work level)
could be very slow due to the need to retrieve log files from the
archive. Crash recovery could also be very slow for the same
reason. " The question is how to understand "the same reason" in
sentence "Crash recovery could also be very slow for the same
reason." Does "the same reason" means "the need to retrieve log
files from the archive"? I think it it should be "the need to
retrieve log files from active log files" because crash recovery
just need read information from active log files, not archive log
files. Is it right?
>>James
Hi James,
"the same reason" does mean "the need to retrieve log files from the
archive". logsecond= -1 implies infinite logging and to be able to
support that, some active log files may need to be archived (keeping
space free in the log path). Therefore, depending on the amount of
work done, how large the active log window is, etc. log files may
need to be retrieved during crash recovery.
Regards,
Kelly
I am a bit puzzled here as to log file behavior.
Why would the log files have to be retrieved from the archive under
these (or nay conditions). I thought that if log files were active,
they get copied to the archived, but they do not get replaced,
removed, deleted from the the log path until they are fully
archivable.
By this I mean all transactions in the file have been either rolled
back, committed and externalized, and also applied in DPROP if
applicable. Until then, the log file is deemed to be active and must
stay in the log path.
Therefore, I don,t see how it would have to be retrieved from the
archive, even if logsecond=1.
Am I off in left field, lost in log path or what ?????
Thanls, Pierre.
By setting LOGSECOND = -1 (and enabling log archiving via LOGARCHMETH1), you
enable "infinite active logging".
This allows an active unit of work to span primary logs AND archive logs,
allowing a transaction to use an infinite number of log files (hence:
"infinitive active logging"). It is useful to accommodate large jobs that
require more log space than normally would be allocated to the primary logs.
--
Jeroen
ctive logs have to stay in the active log path. They cannot be moved,
erased, deleted, replaced Only copied to the archive.
So, why should one worry about logsecond=-1 and having to retrieve
active logs from the archive ??? That was my question.
Regards, Pierre.
Pierre StJ wrote:
Active logs have to stay in the active log path. They cannot be moved,
erased, deleted, replaced Only copied to the archive.
So, why should one worry about logsecond=-1 and having to retrieve
active logs from the archive ??? That was my question.
Regards, Pierre.
"Active logs have to stay in the active log path"
While his is true for "Archive logging", it isn't for "Infinite Active
logging".
A quote from "Understand ing DB2 - Learning Visually with Examples":
"When archival logging is enabled, a log is archived as soon as it becomes
full. DB2 leaves the log in the log directory until it becomes inactive and
then renames the file for reuse. With infinite logging, DB2 still archives
the log as soon as it is full, but it does not wait for it to become
inactive before it renames the file for reuse. This guarantees that the
active log directory will never fill up, because any logs can be reused once
they are filled. Note that the use of infinite active logging can prolong
crash recovery times as active logs may need to be retrieved from the
archive site."
HTH.
--
Jeroen
Jeroen, thanks very much for clarifying that.
I knew what I was reading had to work but my misunderstandin g didn't
make it make sense.
Now I know better.
Thanks, Pierre.
On Feb 25, 6:34*pm, "The Boss" <use...@No.Spam .Please.invalid wrote:
Pierre StJ wrote:
Active logs have to stay in the active log path. *They cannot be moved,
erased, deleted, replaced Only copied to the archive.
So, why should one worry about logsecond=-1 and having to retrieve
active logs from the archive ??? That was my question.
Regards, Pierre.
"Active logs have to stay in the active log path"
While his is true for "Archive logging", it isn't for "Infinite Active
logging".
A quote from "Understand ing DB2 - Learning Visually with Examples":
"When archival logging is enabled, a log is archived as soon as it becomes
full. DB2 leaves the log in the log directory until it becomes inactive and
then renames the file for reuse. With infinite logging, DB2 still archives
the log as soon as it is full, but it does not wait for it to become
inactive before it renames the file for reuse. This guarantees that the
active log directory will never fill up, because any logs can be reused once
they are filled. Note that the use of infinite active logging can prolong
crash recovery times as active logs may need to be retrieved from the
archive site."
HTH.
--
Jeroen
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