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This doesn't explain the data loss consequences (remember the client default!), nor was it clearly visible on the download page - you'd have to explicitly look for it.

This was the case until as late as 2014: https://web.archive.org/web/20140704182658/http://www.mongod...

And again, the 'download' page or README is not sufficient for such a warning, nor is a startup message a reliable place to put it (because of initscripts and such). It should have been in all the relevant places in the documentation, instead.



Unacknowleged writes were a bad default. I think everyone with a shred of honesty will happily admit to that.

It was certainly in the documentation, in the blog posts, in the startup logs, and in the README for quite a long time. If you missed it, it's probably because you weren't paying attention. Again, there are plenty of good reasons to dislike MongoDB, but this isn't one of them, and harping on it substantially degrades your credibility.


> It was certainly in the documentation, [...] in the startup logs, and in the README for quite a long time.

All the wrong places, as already stated. These are not the places where developers actually look. I provided some better example locations here: https://twitter.com/joepie91/status/622920351731843072

> [...] in the blog posts [...]

Certainly not there. Go look around for MongoDB tutorials from the timespan where unacknowledged writes were the default, and almost none of them remark on the 32-bits limitation.

> If you missed it, it's probably because you weren't paying attention.

Nonsense. It simply wasn't in the locations where people actually look. You can easily verify that using the Wayback Machine (and in fact, this is still mostly the case today).

> Again, there are plenty of good reasons to dislike MongoDB, but this isn't one of them, and harping on it substantially degrades your credibility.

If pointing out extremely dangerous past negligence from the MongoDB developers "degrades my credibility" in your view, then you have some very strange ways to determine credibility.


> All the wrong places, as already stated. These are not the places where developers actually look.

If you're not reading READMEs, installation notes, and server logs and instead depend on marketing splash pages to highlight the limitations of the technologies you use, you're a bad developer. Sorry.

> Certainly not [in blog posts]

http://blog.mongodb.org/post/137788967/32-bit-limitations

> It simply wasn't in the locations where people actually look. You can easily verify that using the Wayback Machine (and in fact, this is still mostly the case today).

I first started using Mongo in 2010 according to my gitlogs (after it having been on my radar for some time before that), and I very distinctly remember reading about the 32-bit limitation well before I'd ever installed it, because we were also using Varnish at the time, which has similar issues on 32-bit systems because it too uses (or at least, at that time used) memory-mapped files.

The claim that the limitation was not documented well, or was hidden, or was generally unknown at that time is just simply false.


The word 'loss' does not appear on that page. There's a world of difference IMO between a rejected operation (which is what I would assume from that description – that the address space exhaustion would be detected and the database would stop accepting writes) and irreversible data loss.


That's a consequence of their unacknowledged writes default - any write which failed for any reason wouldn't result in a rejection as far as the client is concerned (because the default was to shove the write request into the pipe and then continue without waiting for acknowledgement). As I mentioned earlier, most everyone acknowledges (heh) that as a bad default.

If you were checking getLastError on your writes, you would see the write fail when you ran out of address space.


I guess any substantially-advanced failure mode is bound to be multi-factorial. Makes sense; thanks for the reply.


> Unacknowleged writes were a bad default.

Bad defaults? It was defended as "this is ok because system is distributed" and there was a joke about it helping ace all the silly benchmarks. So it wasn't "oops we forgot to uncomment out the fsync line in the code". It was a deliberate decision.

It was deceptive, and that is why many people hate MongoDB and wouldn't let it get even close to their data -- because have a track record of lying about the capabilities of their system.


Also don't forget that almost every driver ignored the defaults and used acknowledged writes anyway.




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