[Info-vax] Databases versus RMS

[Arne Vajhøj]

On 4/22/2012 11:49 AM, Paul Sture wrote:
> On Sat, 21 Apr 2012 21:55:56 -0400, Arne Vajhøj wrote:
>> On 4/21/2012 12:44 PM, Paul Sture wrote:
>>> On Wed, 18 Apr 2012 08:40:50 -0500, Bob Koehler wrote:
>>>>      But I still find it a PITA to have to sprinkle fsynch calls all
>>>>      through my UNIX code when I want to decrease the buffering.
>>>
>>> You might enjoy these discussions where Linus Torvalds got upset over
>>> Ext3 and Ext4 behaviour:
>>>
>>> http://bit.ly/JcDKvX
>>>
>>> "if you write your metadata earlier (say, every 5 sec) and the real
>>> data later (say, every 30 sec), you're actually more likely to see
>>> corrupt files than if you try to write them together... This is why I
>>> absolutely detest the idiotic ext3 writeback behavior. It literally
>>> does everything the wrong way around -- writing data later than the
>>> metadata that points to it. Whoever came up with that solution was a
>>> moron. No ifs, buts, or maybes about it."
>>>
>>> And one comment I particularly like:
>>>
>>> http://bit.ly/JcDGMK
>>>
>>> --- start quote ---
>>>
>>> Difficult to have an ACID-compliant db when you don't have an ACID-
>>> compliant fs.
>>>
>>>
>>> I read Ted T'so's response pointed to by Charlie, above. This bit of
>>> reasoning has me laughing:
>>>
>>>> This sounds like a good thing, right? It is, except for badly written
>>>> applications that don’t use fsync() or fdatasync(). Application
>>>> writers had gotten lazy, because ext3 by default has a commit interval
>>>> of 5 seconds, and and uses a ...
>>>
>>> Those damn application writers! The nerve of them to assume that the
>>> file system might actually store their data in reasonable time! What
>>> will they expect next? A database that stores data? An operating system
>>> that run the computer?
>>> /sarcasm
>>
>> I believe that you can disable the writeback caching at mount time.
>
> Indeed you can.  The trouble was that at the beginning of 2011 you had to
> know about this problem and put a more sensible value into your fstab
> yourself, for the default on ext4 at least wasn't the safest choice.

Maybe the logic is that they expect people that setup database systems
to read documentation.

Arne