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| Queue manager starting with different logs |
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| sunny_30 |
 Posted: Mon Aug 25, 2008 7:05 pm Post subject: |
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Master
Joined: 03 Oct 2005
Posts: 258
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Gaya said:
| Code: |
| all the persistent messages of a queue manager are written on logs |
Akanksha said:
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| only persistent msgs can survive QM failure... and are stored in logs... |
not quite true when the logging used is 'circular'
look at what PeterPotkay said:
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| Create a QM with circular logs of 10MB in total. Now go ahead and put 5GB of persistent messages into that QM that has only 10MB of circular logs. |
This example makes sense of everything.
If 5GB of persistent messages are put to a queue where circular-logging is used, say the messages are sitting on the queue & not picked up.
How can the 10MB circular-logs hold 5GB persistent messages sitting on queue?
But when the QM is restarted still the messages are replayed onto the 5GB queue.. how? from the queue-file! not circular-log!!
If it is linear-logging, yes all persistent-messages are replayed from log.
If it is circular-logging, all persistent 'committed' messages are replayed from queue-file & 'uncommitted' messages from log.
The circular log only stores uncommitted persistent messages (the ones not written to queue yet) only.
If the log-size is bigger, the large -messages are written to queue faster.
This is what I think how the logging works,
I might be wrong, please correct if Im
//Sunny |
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| gbaddeley |
| Posted: Tue Aug 26, 2008 11:07 pm Post subject: |
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Jedi Knight
Joined: 25 Mar 2003
Posts: 2538
Location: Melbourne, Australia
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| sunny_30 wrote: |
If 5GB of persistent messages are put to a queue where circular-logging is used, say the messages are sitting on the queue & not picked up.
How can the 10MB circular-logs hold 5GB persistent messages sitting on queue?
But when the QM is restarted still the messages are replayed onto the 5GB queue.. how? from the queue-file! not circular-log!!
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The queue-file contains all the committed messages across the restart. They do not need to be replayed in any sense of the word.
Messages that have been committed are never accessed again on the logs. Old linear logs which do not contain any uncommitted messages can therefore be deleted without any loss of recoverability.
If the QM went down in the middle of a UOW, uncommitted messages will be reconciled at restart using the logs.
| Quote: |
| If the log-size is bigger, the large -messages are written to queue faster. |
Only in the sense that they won't need to span multiple log files.
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Glenn |
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| atheek |
| Posted: Sun Aug 31, 2008 5:06 am Post subject: |
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Partisan
Joined: 01 Jun 2006
Posts: 327
Location: Sydney
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| gbaddeley wrote: |
Old linear logs which do not contain any uncommitted messages can therefore be deleted without any loss of recoverability.
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I thought linear logging is used primarily for media recovery ( that is when Q file gets damaged ) rather than just for transactional recovery..so I may still require Old linear logs which do not contain any uncommitted messages, but has recorded one persistent message which still sits in the queue waiting to be consumed by the application...However it wont be required once a new checkpoint has occured or a new media image created using rcdmqimg |
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| gbaddeley |
| Posted: Sun Aug 31, 2008 5:34 pm Post subject: |
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Jedi Knight
Joined: 25 Mar 2003
Posts: 2538
Location: Melbourne, Australia
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| atheek wrote: |
| I thought linear logging is used primarily for media recovery ( that is when Q file gets damaged ) rather than just for transactional recovery..so I may still require Old linear logs which do not contain any uncommitted messages, but has recorded one persistent message which still sits in the queue waiting to be consumed by the application...However it wont be required once a new checkpoint has occured or a new media image created using rcdmqimg |
Yes, media recovery requires all the logs back to when the last record-image was done for the object. Hence there are two criteria for determining if old linear logs need to be kept, restart from qmgr failure, and media recovery.
Chapter 5 "Recovery and problem determination" of the "WebSphere MQ System Administration Guide V7.0" describes everything in gory detail.
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Glenn |
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