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MongoDB queries don’t always return all matching documents

engineering.meteor.com

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Re: MongoDB queries don’t always return all matching documents

#41

Post by eloff »

im_down_w_otp wrote: post #16

Said it before, will say it again... "MongoDB is the core piece of architectural rot in every single teetering and broken data platform I've worked with." The fundamental problem is that MongoDB provides almost no stable semantics to build something deterministic and reliable on top of it. That said. It is really, really easy to use.

As a guy who works on ACID database internals, I'm appalled that people use MongoDB. You want a document store? Use Postgres. Why on earth would you use a database that makes so little in the way of guarantees about what results you get from it? I think most people have really low load and concurrency, so things seem to work. When things get busier you're in for a world of pain. Look I get that's it's easy to use and easy to get started with, but you're going to pay for all of that later.

Re: MongoDB queries don’t always return all matching documents

#43

Post by glasser »

TimPrice wrote: post #34

The article is interesting, but title is fud. Besides, all this is not unexpected: > How does MongoDB ensure consistency? > Applications can optionally read from secondary replicas, where data is eventually consistent by default. Reads from secondaries can be useful in scenarios where it is acceptable for data to be slightly out of date, such as some reporting applications. https://www.mongodb.com/faq

This is not related to reading from secondaries. This issue can occur in single node systems.

Re: MongoDB queries don’t always return all matching documents

#44

Post by ht85 »

ruw1090 wrote: post #22

While I love to hate on MongoDB as much as the next guy, this behavior is consistent with read-committed isolation. You'd have to be using Serializable isolation in an RDBMS to avoid this anomaly.

The article suggests that tuples being moved to different storage locations can cause them to not show up in a table scan.

No such thing can happen in a sane RDBMS, no matter the transaction isolation level.

Re: MongoDB queries don’t always return all matching documents

#45

Post by stevecalifornia »

Joeboy wrote: post #9
lossolo wrote: post #4

I've just migrated one project from mongo to postgresql and i advise you to do the same. It was my mistake to use mongo, after I've found memory leak in cursors first day I've used the db which I've reported and they fixed it. It was 2015.. If you have a lot of relations in your data don't use mongo, it's just hype. You will end up with collections without relations and then do joins in your code instead of having db…

> don't use mongo, it's just hype I'm kind of curious as to where this hype is. I've almost never heard anybody say anything positive about mongodb. All I ever see is people saying it's terrible / hilarious for various reasons.

When it first came out it was hyped big time. Every other article was about how great Mongo was. About a year later the fallout started bubbling up. Digg went down for one or two weeks because of switching over to Mongo-- Reddit saw an influx of users and now is what it is.

Re: MongoDB queries don’t always return all matching documents

#46

Post by the_mitsuhiko »

ruw1090 wrote: post #22

While I love to hate on MongoDB as much as the next guy, this behavior is consistent with read-committed isolation. You'd have to be using Serializable isolation in an RDBMS to avoid this anomaly.

With read-committed you see the old state.

Re: MongoDB queries don’t always return all matching documents

#47

Post by simtel20 »

stevecalifornia wrote: post #45
Joeboy wrote: post #9

Earlier quoted context omitted.

> don't use mongo, it's just hype I'm kind of curious as to where this hype is. I've almost never heard anybody say anything positive about mongodb. All I ever see is people saying it's terrible / hilarious for various reasons.

When it first came out it was hyped big time. Every other article was about how great Mongo was. About a year later the fallout started bubbling up. Digg went down for one or two weeks because of switching over to Mongo-- Reddit saw an influx of users and now is what it is.

I recall that Digg moved at least some part of their site to cassandra. Did they in fact do both?

Re: MongoDB queries don’t always return all matching documents

#48

Post by throwaway420 »

Joeboy wrote: post #9
lossolo wrote: post #4

I've just migrated one project from mongo to postgresql and i advise you to do the same. It was my mistake to use mongo, after I've found memory leak in cursors first day I've used the db which I've reported and they fixed it. It was 2015.. If you have a lot of relations in your data don't use mongo, it's just hype. You will end up with collections without relations and then do joins in your code instead of having db…

> don't use mongo, it's just hype I'm kind of curious as to where this hype is. I've almost never heard anybody say anything positive about mongodb. All I ever see is people saying it's terrible / hilarious for various reasons.

Like with any online community, Hacker News can be kind of an echo chamber where groupthink reigns and alternative points of view aren't encouraged. MongoDB hype has died down here, but there are still some people that are fans.

There are some things MongoDB does fairly well:

* MongoDB is really easy to use

* Document databases can be great and flexible solutions for some kinds of projects

* Documentation is fairly good so learning the basics isn't too hard even if you know nothing about it

* scales fairly well at the initial stages

* arguably quicker to get a project off of the ground with than traditions RDBMs, which might be the most important consideration for any startup even if a complete rewrite would eventually need to take place

That being said, I've used MongoDB significantly before and it wouldn't be my first choice for most types of new project: PostgreSQL probably would be

Re: MongoDB queries don’t always return all matching documents

#49

Post by williamstein »

sotojuan wrote: post #33
lossolo wrote: post #4

I've just migrated one project from mongo to postgresql and i advise you to do the same. It was my mistake to use mongo, after I've found memory leak in cursors first day I've used the db which I've reported and they fixed it. It was 2015.. If you have a lot of relations in your data don't use mongo, it's just hype. You will end up with collections without relations and then do joins in your code instead of having db…

Even if you want NoSQL I'd use RethinkDB over Mongo any day. Way better query language, real-time support, and relational/regular SQL-like stuff. https://rethinkdb.com/docs/comparison-tables/

And the use case of this post is exactly what RethinkDB does better: "One of our services periodically polls the database and reads the list of running containers with the query..."

Re: MongoDB queries don’t always return all matching documents

#50

Post by PeCaN »

eloff wrote: post #41
im_down_w_otp wrote: post #16

Said it before, will say it again... "MongoDB is the core piece of architectural rot in every single teetering and broken data platform I've worked with." The fundamental problem is that MongoDB provides almost no stable semantics to build something deterministic and reliable on top of it. That said. It is really, really easy to use.

As a guy who works on ACID database internals, I'm appalled that people use MongoDB. You want a document store? Use Postgres. Why on earth would you use a database that makes so little in the way of guarantees about what results you get from it? I think most people have really low load and concurrency, so things seem to work. When things get busier you're in for a world of pain. Look I get that's it's easy to use and…

MongoDB: Because /dev/null doesn't support sharding.
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