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I fail to understand how and why silent failure is considered a reasonable default.



It actually happens in some scenarios.

Let's say, outside of the tech world: When you send a post card (cheap ones) to a friend, you won't receive any delivery confirmation. You just send it and go do whatever you please, believing the post card will be there. If the envelope don't get there, no biggies, you will send another on your next trip anyways. No hurt feelings.

But, let's say you need to send me a check. You want to know if I received it or not, specially because sometimes I don't cash checks right away. Without confirmation it would be difficult to you to decide if you cancel the previous check and send another, or do nothing, because I could be at that very time trying to cash the check or it could be lost somewhere. The delivery confirmation is an add-on where you receive a confirmation that the envelope got there, but see, it will take time for that confirmation to arrive. It's expensive. If you are sending a 0.01 check, you can just send another if the recipient asks.


Databases are not like the mail. Databases are like a bank.

If I ask my bank why my account does not reflect my latest deposit and they say 'Sorry, I guess we didn't get it', I'm getting a new bank.


...and if you're building a banking app, that's relevant. If you're building a chat system, maybe things other than data integrity matter more.


Is it not relevant for a blog? Your business website? Your toy application? It is even relevant for a chat system!

And the flaw of your argument: Even if there are other more important things for an application, let's just make anything else than the #1 feature shit.


I'm just saying some databases are like the mail. A chat system is one such case.

And the flaw of your argument: Even if there are other more important things for an application, let's just make anything else than the #1 feature shit.

I don't actually understand what you mean, here, but since you say it's the flaw of my argument, I'm very interested in it. Could you rephrase briefly?


Is it actually unimportant if a chat message is dropped? It seems damn important to me, what use is a chat app if someone sends you an important message and you never receive it? I could see that being true for something like anonymized logs where you are only going to be looking at it in aggregate, but just silently ignoring chat messages really doesn't seem acceptable to me.


Well, in practice, it's not too uncommon to send chat messages or SMS messages that just vanish, or arrive out of order, or arrive the day after they were sent. People do not, then, say that SMS is completely useless; instead, they accept that once in a while a message won't get through, and that they should call if it's important.

I'm not saying it's not at all important that chat messages actually get sent, and if it happens every single day to a user, then they might well look for alternatives, but it's not of the same importance as losing a banking transaction. If accepting that occasional writes will be dropped on the floor allows you to get your product out in October instead of December, that could be an acceptable tradeoff. Certainly not every use case is like this, but some are.


I mean is it desirable behaviour? Would you not want a chat program which never dropped your messages? If that's the case, we should work towards it, not accept a 1 of 1000 messages lost because "there are more important things to worry about". The most important feature should be prioritized over less important ones, but it should not make us forget them - they should be as good as possible as well.

I guess what I'm trying to say is this: You cannot ignore all the other features except the biggest one.


Not really, in my experience. Losing chat messages or logs is among the worst things a chat application can do.

I take your point though, but I think consistency is still one of the most important attributes for anything that is going to store data. Why even use a database, if your data matters so little? Just throw it into memory or memcache.


Better analogy: You ask about the deposit not reflected and they say "Sorry, you didn't choose the account option to prevent the money from vanishing. It was noted in the fine print; didn't you read it?" Then you get a new bank.


Surely you don't think that this is a reasonable model for how a database should work, do you?


If you can turn that behavior on and off (by using getLastError or whatever), why not have this feature?

If I'm logging upvotes on a post or comments on a blog, which is about as serious as 99% of these b.s. startups are doing, I think it's fair to ignore errors.

I do agree that this should be pointed out in huge blinking letters though, or be a driver flag that is on by default. The amount of people who don't know this about Mongo, but are still using it to store gigs of data, is horrifying.


  If I'm logging upvotes on a post or comments on a blog, 
  [...] I think it's fair to ignore errors.
Even in that situation, you need to know whether you're discarding 1% of upvotes or 99% of upvotes.


I am reminded of the time, back deep in the past of MySQL, that someone complained about MySQL not providing locks. The development replies amounted to "But it is FAST!" The reply was "But the results are often wrong" and the developers again "But it is FAST!"

Acceptable software, particularly in the class of databases, is obligated to tell you that it didn't complete your request. This is not an option.


The problem has and always will be that MongoDB toes the line between a caching product and a database product, regardless of what 10gen decides to call it. It's extremely frustrating that 10gen can't embrace this fact, and instead perpetuates marketing that causes the product to be perceived as flawed by their target audience. But once you've discovered this, you can use it appropriately (either by overriding the default silent failure to use it as for durable persistence, or only using it for caching or as an eventually consistent store).


Because the whole point of NoSQL movement is that you are storing Facebook "like"s and in fact would be glad if some of them get lost.




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