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From Robert Dionne <dio...@dionne-associates.com>
Subject Re: delayed_commits false
Date Tue, 06 Jul 2010 23:13:27 GMT
Perhaps it's a matter of documentation. Most users aren't going to think about the finer points
of fsync and so forth, but will care about perceived out of the box performance. 

However there will be scenarios where ACID will matter very much and good documentation will
help these users make the tradeoff. I think a key point is that users who do care are not
harmed by the defaults.
 




On Jul 6, 2010, at 6:58 PM, Volker Mische wrote:

> I have to admit that the point, that the main audience of a tarball are developers is
a good one. Perhaps people that do binary distributions of CouchDB (like all the linux distros)
could be encouraged to turn it to false (though I have no idea what their general policy about
changing defaults is).
> 
> Cheers,
>  Volker
> 
> On 07.07.2010 00:52, Mikeal Rogers wrote:
>> I think there is a balance that we can find here between user experience and
>> durability.
>> 
>> I think the biggest question for me is, who is the primary target of the
>> tarball download?
>> 
>> If it's developers, I think we should leave it on.
>> 
>> If it's people who are going to put it up, vanilla, in to production, we
>> should turn them off.
>> 
>> I know that I would certainly advocate keeping them off in the CouchDBX
>> build.
>> 
>> -Mikeal
>> 
>> On Tue, Jul 6, 2010 at 3:46 PM, Volker Mische<volker.mische@gmail.com>wrote:
>> 
>>> On 07.07.2010 00:06, Damien Katz wrote:
>>> 
>>>> 
>>>> On Jul 5, 2010, at 8:49 AM, Volker Mische wrote:
>>>> 
>>>>  Hi All,
>>>>> 
>>>>> delayed_commits were enabled to have better performance especially for
>>>>> single writers. The price you pay for is that you potentially lose up
to one
>>>>> second of writes in case of a crash.
>>>>> 
>>>>> Such a setting makes sense, though in my opinion it shouldn't be enabled
>>>>> by default. I expect* that people running into performance issues at
least
>>>>> take a look at the README or a FAQ section somewhere. There the
>>>>> delayed_commit setting could be pointed out.
>>>>> 
>>>>> I'd like to be able to say that on a vanilla CouchDB it's hard to lose
>>>>> data, but I can't atm. I'm also well aware that there will be plenty
of
>>>>> performance tests when 1.0 is released and people will complain (if
>>>>> delayed_commits would be set to false by default) that it is horrible
slow.
>>>>> Though safety of the data is more important for me.
>>>>> 
>>>>> If the only reason why delayed_commits is true by default are the
>>>>> performance tests of some noobs, I really don't think it's a price worth
>>>>> paying.
>>>>> 
>>>>> *I know that in reality people don't
>>>>> 
>>>>> I would like to see delayed_commits=false for 1.0
>>>>> 
>>>> 
>>>> Last year we turned off delayed commits by default. We got lots of
>>>> complaints, the performance impact was too great. So we switched it back.
We
>>>> aren't the first storage engine to go around on this. For example, Apple's
>>>> core data switched to using full fsyncs for each write in 10.4, but then
>>>> switched it back for 10.5:
>>>> 
>>>> 
>>>> http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/CoreData/Articles/cdPersistentStores.html
>>>> 
>>>> "Important: The default behaviors in Mac OS X v10.4 an 10.5 are different.
>>>> In Mac OS X v10.4, SQLite uses FULL_FSYNC by default; in Mac OS X v10.5 it
>>>> does not."
>>>> 
>>>> Anyway, we can improve the documentation warning's, etc, but we should
>>>> stay with the current defaults.
>>>> 
>>>> -Damien
>>>> 
>>>> 
>>> As 1.0 is approaching fast, I think this discussion is pretty important.
>>> Especially this thread showed that there are people that prefer setting
>>> delayed_commits to false. Although sometimes someone has to make the last
>>> call, and there is probably no one better than the creator of the project, I
>>> think it this case the decision should be made by more people.
>>> 
>>> For *me personally* the authority of Apache CouchDB are the committers. I
>>> would love to see them vote on this topic (being it public or private
>>> doesn't matter).
>>> 
>>> Cheers,
>>>  Volker
>>> 
>> 
> 


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