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
