[MacLoggerContest] Journalling

[Jack Brindle]

A short bit of clarification, then. Make no assumptions as to what I 
may be referring. I won't claim to know what problem journalling may be 
solving. I won't claim to know how it may be solving that problem. I 
won't even claim to know why Apple added journalling to the Mac's file 
system!

I simply want to know what the problem is that needs to be solved, and 
apparently has been solved in the past with journalling.

On Mar 2, 2005, at 10:46 AM, Jonathan G0DVJ wrote:

>
> Interesting discussion ...
>
> Are we mixing up two meanings of Journalling?  Maybe John mentioned it 
> in the general sense of keeping a journal record of QSO data so that 
> nothing is lost.  i.e. at the application level.  There is also the 
> OSX specific meaning of Journalling which was introduced in Panther 
> and which is a system-wide volume configuration aspect under admin 
> user control at disk set-up time, and not the application.   Not sure 
> if Jack is alluding to this in his posting?
>
> I agree that the simplest way seems to be to write then flush from the 
> application's viewpoint.  However maybe this is another area where we 
> should just state what the user experience should be and leave it to 
> Don to decide how best to implement things to achieve it, like Jack 
> rightly pointed out when I mentioned multi-threading in an earlier 
> post!
>
> I think we all agree with John's original point about losing nothing 
> from the committed log - Most other systems I have used cannot 
> guarantee that the current QSO still being entered (i.e. not 
> completed/committed) won't be lost, but that is the most one can lose.
>
> 73,
> Jonathan.
> --
>
> On Mar 2, 2005, at 6:44 am, Jack Brindle wrote:
>
>>
>> On Feb 28, 2005, at 1:56 PM, John Bastin wrote:
>>
>>> Automatic journaling, so even if you have a power failure, NOTHING 
>>> is lost.
>>
>> This grabbed my attention - I'd like to drill into it a bit to 
>> understand exactly what is being asked for and why. More importantly, 
>> I want to understand the current need for journalling, because I 
>> don't think I understand it properly now.
>>
>> Under MacOS X information written to files may be immediately flushed 
>> to disk. When writing a log file, the data may be appended to the log 
>> file and saved to disk immediately. As I understand journalling, the 
>> information is written to the journal file, then to the log file. In 
>> this case a power failure before the journal write would lose the 
>> entry, while one in-between the two writes will simply cause a 
>> journal-to-log file update on restart. But, the information that 
>> would be appended to the log file could have been handled in place of 
>> the journal write, taking care of the whole thing at once. In both 
>> cases, power failures before the first write completes causes the 
>> entire entry to be lost, while a failure after the first write 
>> completes just causes the operator to be rather unhappy.
>>
>> It seems that the simplest way to handle things would be to write the 
>> log entry to the file and immediately flush the file to disk. Is this 
>> too simple? What am I missing?
>
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-Jack Brindle, W6FB
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