Re: RDBMS Feature Matrix (FAQ in the works !!!)

From: Daniel Druker <ddruker_at_agsm.ucla.edu>
Date: 22 Mar 93 11:45:25 PST
Message-ID: <1993Mar22.114525.26838_at_mic.ucla.edu>


>
>Among the long list of features I have extracted these three.
>I think I understand shared and multiplexed log files (and how
>that is basically the same thing.) What I don't understand
>is the multiple log files.
>
>Are you saying that Oracle (v7 ?) allows you to configure
>multiple REDO log files (for the same database) all of which
>can be used simultaneously? I am aware of how multiple files
>can be configured into a single logical file and how they are
>used serially, but that's not what I would call multiple log
>files since only one file is active at any time.
>
>>10. Shared Log Files Y
>>37. Multiplexed Log Files Y
>>46. Multiple Log Files Y
>>
 

I interprete this to imply the following distinction between single and multiple log files.

A RDBMS that implements redo recovery and transaction logging using a single log file (Or a single group of mirrored files) may be in danger if that single log file fills up. That is, if the single log fills without being backed up the typical system behavior is to A) Freeze, or B) Start rolling back all long-running transactions arbitrarilly. There are also performance issues if the RDBMS performance slows (or if the DBMS must be shut down) while backing up the single log file.

A RDBMS that implements multiple log files (or sets of log files) switches from one to the next when a log fills. This prevents a database from ever dying because of a full log, since the filled logs are automatically archived and made ready for re-use in a circular fashion. If the operator failed to mount tapes and ALL the logs filled, an extra log could be added to allow continued operation while the old logs were being backed up.

Other opinions/interpretations happily accepted.

Does this help ?

  • Dan

Daniel Druker
Anderson Graduate School of Management at UCLA                    


| Dan Druker                                                               |
| agsm mail 	: ddruker                                                  |
| internet 	: ddruker_at_agsm.ucla.edu                                    |
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Disclaimer: None. I'm a student now and I don't care what you think. Received on Mon Mar 22 1993 - 20:45:25 CET

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