MongoDB 2.6 Released • Hacker News Board

Re: MongoDB 2.6 Released

#21

Post by saurik » Tue, Apr 08, 2014, 2:42 PM UTC

outside1234 wrote: post #17

tedchs wrote: post #16

Will MongoDB still segfault under certain circumstances?

Everything will segfault under certain circumstances.

The only reasonable assumption is circumstances that do not involve hardware failure, the binary being compiled incorrectly, the source code being modified or replaced by someone downstream, the libraries it is using being corrupt or having been replaced by ABI-incompatible variants... none of these are reasonable circumstances; one would then further assume that the person posting has run into reasonable circumstances where MongoDB often crashes, which is not a stretch given the number of bugs that are filed against it that talk about this kind of issue.

https://www.google.com/search?q=site:jira.mongodb.org+mongod...

Re: MongoDB 2.6 Released

#22

Post by rainmaking » Tue, Apr 08, 2014, 2:42 PM UTC

I have never understood how the definition of "Document Database" is different from "File System".

Re: MongoDB 2.6 Released

#23

Post by ericcholis » Tue, Apr 08, 2014, 2:43 PM UTC

anvarik wrote: post #12

With this release aggregation framework got super powerful. Now it returns a cursor. Now we can get the aggregation results and iterate over them. No more 16mb result limitation as well...

Agreed, it was annoying to have to use the MapReduce for larger sets.

Re: MongoDB 2.6 Released

#24

Post by leif » Tue, Apr 08, 2014, 2:43 PM UTC

wilsonfiifi wrote: post #6

So does this mean document level locking has been implemented or just the foundation for its future implementation has been laid? I can't hold my breath much longer! :-) Edit: docs don't make any mention of it but then again they probably haven't updated them yet (fingers crossed!) http://docs.mongodb.org/manual/faq/concurrency/#what-type-of...

It means the foundation has been laid. 2.6 included a lot of refactoring and rewriting of some core subsystems, with the apparent goal of eliminating technical debt so they can make more impactful changes in 2.8.

Don't asphyxiate, tokumx has document-level locking right now. http://github.com/Tokutek/mongo

Re: MongoDB 2.6 Released

#25

Post by z92 » Tue, Apr 08, 2014, 2:43 PM UTC

danielrpa wrote: post #8

A lot of hype... And we still have db level locking. If document level is too difficult, at LEAST do collection level (not that it is too much better, but least it some real improvement).

I was reading somewhere that Mongo can't do document level/record level locking because of mmap'ed files. The whole database is memory mapped. And mmap doesn't understand underlined data structure, it views the whole file as a large single blob.

Ditching mmap will not be that easy, cause most of the speed and simplicity of Mongo comes from using mmap.

Re: MongoDB 2.6 Released

#26

Post by Kiro » Tue, Apr 08, 2014, 2:44 PM UTC

danielrpa wrote: post #8

A lot of hype... And we still have db level locking. If document level is too difficult, at LEAST do collection level (not that it is too much better, but least it some real improvement).

I don't know anything about MongoDB but can you give an example where DB level locking is a problem?

Re: MongoDB 2.6 Released

#27

Post by decentrality » Tue, Apr 08, 2014, 2:45 PM UTC

rainmaking wrote: post #22

I have never understood how the definition of "Document Database" is different from "File System".

It's very close to JSON objects. In fact, it uses JSON/BSON. So it's Hashes of data structures, which MongoDB makes accessible quickly, like a file system must be.

You can also use GridFS to store files in the document database, which actually breaks files into chunks and stores them in collections, also just like a FAT table.

Re: MongoDB 2.6 Released

#28

Post by herge » Tue, Apr 08, 2014, 2:46 PM UTC

rainmaking wrote: post #22

I have never understood how the definition of "Document Database" is different from "File System".

Really? Have you ever tried to search for specific content in structured documents on a filesystem?

Re: MongoDB 2.6 Released

#29

Post by mutex007 » Tue, Apr 08, 2014, 2:47 PM UTC

rainmaking wrote: post #22

I have never understood how the definition of "Document Database" is different from "File System".

In the case of MongoDB, dump a blob called BSON which itself can be larger than the JSON itself. Paradoxically this is touted as a space efficient binary serialization you then read it back using an index or something.

Re: MongoDB 2.6 Released

#30

Post by hamxiaoz » Tue, Apr 08, 2014, 2:50 PM UTC

Playing with Meteor and mongo recently and have found mongo seems a little bit strange from a transitional SQL point of view, like do I need to embed or reference? Can anyone recommend a good book or source?