

New MongoDB alerts and advisories page - ehwizard
http://alerts.mongodb.org/

======
tedsuo
I read recently that mongo has a global lock on write. That was news to me,
does anyone have more info?

~~~
ehwizard
Currently, there is a global read/write lock. MongoDB does extensive yielding
and tracking of on vs. off disk to mitigate the effects of this. In subsequent
versions (2.2) , we'll be lowering the scope of this lock as well.

~~~
jcapote
So only one read at a time?

~~~
cheald
You can read concurrently, but the write lock will block read locks.

[http://www.mongodb.org/display/DOCS/How+does+concurrency+wor...](http://www.mongodb.org/display/DOCS/How+does+concurrency+work)

~~~
e1ven
If you have a lot of writes, this is a KILLER. You need to be very careful
here.

Note, even with Read-Slaves, you are STILL blocked, since each write
replicates to each Read-Slave, and counts as a blocking-write on that slave
while it replicates in.

We dramatically increased application performance when we refactored to remove
a lot of little writes for things like caching, and moved them to memcache.

~~~
tedsuo
Does this make mongo a bad choice for storing real time statistics?

~~~
moe
You always have to benchmark for your own use-case.

This is even more true for mongo than for other databases because mongo
doesn't degrade very well; when you overload it with writes it will
effectively grind to a halt.

This is documented e.g. in the clustrix benchmark:
[http://sergei.clustrix.com/2011/01/mongodb-vs-clustrix-
compa...](http://sergei.clustrix.com/2011/01/mongodb-vs-clustrix-comparison-
part-1.html)

------
carterschonwald
Is this page new as of this past week [edit: its new as of today]? Either way,
every large software project should always try to have some standard page for
this sort of information, so kudos to them for now having one (and its a
visible link on the homepage too).

~~~
dm_mongodb
it's new.

