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Bulk Logged recovery model Expand / Collapse
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Posted Monday, April 16, 2012 9:23 AM
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I got it wrong for legitimate reasons as I assumed the question was referring to log backups and not log files, and thought because bulk recovery model minimally logs bulk operations that both the log file and log backup file would be smaller so, from that angle, thanks for the question as I learned something new. However, in rereading the question I can certainly understand why some people would've received a different interpretation thus thought the question was asking about the log file and not the log backup file, but it's not as though this was the first poorly worded question we've had... :) that being said, I WANT MY POINT BACK, HULK SMASH
Post #1284202
Posted Monday, April 16, 2012 9:35 AM
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call.copse (4/16/2012)
sknox (4/16/2012)
call.copse (4/16/2012)
I would go further than the other posters on this thread - sorry, this question and the answer given are just plain WRONG.

See this MSDN blog entry which clearly explains log sizes in different modes:
http://blogs.msdn.com/b/suhde/archive/2010/12/29/transaction-log-backup-size-in-bulk-logged-recovery-model.aspx

The LOG FILE BACKUP is certainly likely to be larger.

The LOG FILE (subsequent to backup) is almost certainly SMALLER given that it is not doing point in time restore.

I will accept that the question could have been mangled unintentionally in the editorial prcess or something - but, the fact remains, the correct answer to the question as written is NO.


I would say that since the question read "...could you see a log file bigger than usual?" the only logical answer is yes. While the bulk-logged recovery model is a feature designed to reduce log file growth, it does not constrain log file growth. Therefore you certainly could see a larger log file in some circumstances.

However, I would also say that that does not seem to be the intent of the question. The question was poorly worded, but the explanation is correct. So, poor wording of the question has given us a "If False then True" situation -- which, if my memory of basic logic serves me properly, is still True. So much for logic.


I disagree. There are no circumstances where immediately post log backup, a full recovery model database log file will be less big than a bulk logged model database log file after the same set of transactions. I am pretty sure there are few conceivable circumstances where it might even be the same size. The blog link I sent above explains this pretty well.


The question did not ask if the log file would be bigger that a log file generated from a full recovery model database with the same set of transactions. The question asked if the log file could be bigger than usual. In this context, the logical interpretation of "usual" would be the average log file size preceding the model change. A single unusual non-bulk-logged transaction could account for that.
Post #1284210
Posted Monday, April 16, 2012 9:56 AM
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I guessed right, on the basis that if the answer was No then it wouldn't be a very interesting question

It then prompted me to read up a bit on bulk logging, so from my perspective was a good question.
Post #1284238
Posted Monday, April 16, 2012 7:38 PM
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Post #1284635
Posted Monday, April 16, 2012 7:38 PM
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Post #1284636
Posted Monday, April 16, 2012 7:38 PM
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Post #1284637
Posted Tuesday, April 17, 2012 12:57 AM


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Got it wrong, because I didn't know log file and log backup apparently are the same thing.
Anyhow, it made me think, so a part of the question was succesfull.




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Posted Tuesday, April 17, 2012 2:32 AM


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sknox (4/16/2012) The question did not ask if the log file would be bigger that a log file generated from a full recovery model database with the same set of transactions. The question asked if the log file could be bigger than usual. In this context, the logical interpretation of "usual" would be the average log file size preceding the model change. A single unusual non-bulk-logged transaction could account for that.


True enough - if you are getting away from the intent to cover the backup issue I think the wording is loose enough to accept that interpretation - although if you accept that interpretation then you have to say full recovery model vs bulk is a complete red herring and has nothing to do with the actual question or answer. The question is then simply 'could your log be bigger than usual?' which is pretty pointless, which is why I took the interpretation 'would the log file be bigger than a log file generated from a full recovery model database with the same set of transactions'.
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Posted Tuesday, April 17, 2012 7:33 AM
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sknox (4/16/2012)

I would say that since the question read "...could you see a log file bigger than usual?" the only logical answer is yes. While the bulk-logged recovery model is a feature designed to reduce log file growth, it does not constrain log file growth. Therefore you certainly could see a larger log file in some circumstances.

However, I would also say that that does not seem to be the intent of the question. The question was poorly worded, but the explanation is correct. So, poor wording of the question has given us a "If False then True" situation -- which, if my memory of basic logic serves me properly, is still True. So much for logic.


This is pretty much the way I looked at this question. The key word to me was could as well, which pretty much forces the answer to be yes because it is such an open-ended question. I'm thinking along the lines of Arthur C. Clarke's first law:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
Post #1284913
Posted Tuesday, April 17, 2012 12:26 PM


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Ernie Schlangen (4/17/2012)
sknox (4/16/2012)

I would say that since the question read "...could you see a log file bigger than usual?" the only logical answer is yes. While the bulk-logged recovery model is a feature designed to reduce log file growth, it does not constrain log file growth. Therefore you certainly could see a larger log file in some circumstances.

However, I would also say that that does not seem to be the intent of the question. The question was poorly worded, but the explanation is correct. So, poor wording of the question has given us a "If False then True" situation -- which, if my memory of basic logic serves me properly, is still True. So much for logic.


This is pretty much the way I looked at this question. The key word to me was could as well, which pretty much forces the answer to be yes because it is such an open-ended question. I'm thinking along the lines of Arthur C. Clarke's first law:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

The trouble is that to many people (including me) it looks as if the question means "is it at all likely that the decision to switch to bulk mode increases the size of" whatever it refers to. If it refers to the log file (which is what it says) the answer is clearly NO. If it refers to the backup file (which is what the question author says he intended) the answer is clearly YES.

And yes, regardless of Clark's law I will state that it is extremely unlikely that a switch to bulk logging will cause an increase in the log file size, and that it's equally unlikely that it won't cause an increase in the log backup size. If you believe Clarke's law you will probably want to claim that when I (an elderly scientist - on whether distinguished or not I make no comment) say that it is impossible that switching to bulk logged mode then doing a bulk operation then switching back to full mode and then doing a backup will lead to a smaller backup file that doing all the same except that the recovery mode switches are omitted I am likely to be talking from the wrong orifice, and that probable mistake on your part just goes to show that Clarke's law is (exactly as he intended) a broad generalisation that can't be used to determine specific outcomes although it can be used to indcate that unvalidated theories (as opposed to empirical knowledge) are often a waste of space.

Edit: eliminate double negatives (Cha toigh leam a' bheurla shasunnach - I hate the English gibberish).


Tom
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