Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Things I wish I knew about MongoDB a year ago

snmaynard.com

Post reply on HN
Print view View original

41–50 of 111 posts

Re: Things I wish I knew about MongoDB a year ago

#41

Post by vidarh »

joevandyk wrote: post #27
thibaut_barrere wrote: post #13

Earlier quoted context omitted.

MongoDB kicks ass in the following situations (real projects I did as a freelancer): - dealing with semi-structured input (forms with some variability) and storing as a document, all while being able to query across the data - used as a store to provide very flexible ETL jobs (with ability to upsert, filter/query, geonear etc) For those situations, I would definitely use MongoDB again. As a RDBMS replacement, I would…

fwiw, postgresql 9.2 supports a json datatype. you can efficiently access/query json fields using plv8 ( http://code.google.com/p/plv8js/ ). so you could have: create table form_results ( id serial primary key, data json ); http://pgeu-plv8.herokuapp.com/ has more information.

Very interesting presentation, though the title of "heralding the death of nosql" is either intentionally exaggerating, or indicates the author doesn't understand all the reasons why people go to nosql databases. In fact, the presentation demonstrates why: Postgres has tons of really fantastic, awesome features that next to nobody uses because they are hidden behind layers of SQL-type incantations and/or require various extensions.

Re: Things I wish I knew about MongoDB a year ago

#42

Post by mattparlane »

sausagefeet wrote: post #32
mattparlane wrote: post #23

Earlier quoted context omitted.

My number one reason for choosing MongoDB is replication that just works out of the box and doesn't require either a read lock or shutting down the master to set up a new slave.

As far as I can tell, Riak blows mongo away for this particular criteria.

That's my understanding too, but MongoDB hit the sweet-spot for us, Riak couldn't handle the raw queries-per-second we needed without requiring extra hardware ($$).

Re: Things I wish I knew about MongoDB a year ago

#43

Post by gbog »

vidarh wrote: post #41
joevandyk wrote: post #27

Earlier quoted context omitted.

fwiw, postgresql 9.2 supports a json datatype. you can efficiently access/query json fields using plv8 ( http://code.google.com/p/plv8js/ ). so you could have: create table form_results ( id serial primary key, data json ); http://pgeu-plv8.herokuapp.com/ has more information.

Very interesting presentation, though the title of "heralding the death of nosql" is either intentionally exaggerating, or indicates the author doesn't understand all the reasons why people go to nosql databases. In fact, the presentation demonstrates why: Postgres has tons of really fantastic, awesome features that next to nobody uses because they are hidden behind layers of SQL-type incantations and/or require vari…

So you'd rather install a completely new storage engine and learn to use it than check a doc and install an extension to postgres?

Re: Things I wish I knew about MongoDB a year ago

#44

Post by arielweisberg »

mgummelt wrote: post #12
lars512 wrote: post #8

The inconsistent reads in replica sets is something we've come across with MySQL read slaves as well. I think it's a gotcha of that whole model of replication, rather than a MongoDB-specific issue.

I'm not aware of any database that solves this problem. Is there one? As far as I know, mysql reads must be distributed to the slaves at the application level, which has no knowledge of master/slave inconsistency. I suppose the time delta between master and slave can be queried, but that still doesn't protect from race conditions/inconsistent reads. This is actually why we chose to only utilize slaves for data redund…

Shameless plug (hey Tokutek is doing it), in VoltDB replication is synchronous so it doesn't have this problem.

Latency in the current version is nothing to write home about, but in V3 latency with replication is 600-1000 microseconds. Group commit to disk is every 1-2 milliseconds.

V3 also allows reads to be load balanced across replicas and masters so you gain some additional read capacity from replication. V3 also routes transactions directly to the node with the data so you don't use capacity forwarding transactions inside the cluster.

You get to keep transactions to. Now go figure out what you don't get to keep ;-)

Re: Things I wish I knew about MongoDB a year ago

#45

Post by jvehent »

joevandyk wrote: post #27
thibaut_barrere wrote: post #13

Earlier quoted context omitted.

MongoDB kicks ass in the following situations (real projects I did as a freelancer): - dealing with semi-structured input (forms with some variability) and storing as a document, all while being able to query across the data - used as a store to provide very flexible ETL jobs (with ability to upsert, filter/query, geonear etc) For those situations, I would definitely use MongoDB again. As a RDBMS replacement, I would…

fwiw, postgresql 9.2 supports a json datatype. you can efficiently access/query json fields using plv8 ( http://code.google.com/p/plv8js/ ). so you could have: create table form_results ( id serial primary key, data json ); http://pgeu-plv8.herokuapp.com/ has more information.

It's just a JSON syntax validator. You can't index on part of the json, postgres treats it as a string.

You can apply full text search on it, but that doesn't tell you if you're matching on a key or a value.

Re: Things I wish I knew about MongoDB a year ago

#46

Post by mgummelt »

sausagefeet wrote: post #33
mgummelt wrote: post #24

Earlier quoted context omitted.

Does Riak support distributed transactions? If not, I don't see how they handle the possibility of a read occuring during the replicated write.

No, Riak is nontransactional. But neither is mongo if it's important here. Riak is apparently getting some kind of strong consistency though. Calvin looks interesting for a nosql with distributed transactions.

This is also something we desperately needed at my last company, but we couldn't find FOSS that supported it. mysql offers XA, but I've heard mixed reviews.

Re: Things I wish I knew about MongoDB a year ago

#48

Post by ww520 »

dleblanc wrote: post #28
diminoten wrote: post #11

Earlier quoted context omitted.

Mongo isn't so important to this question as ODB vs RDBMS. Here's some light reading: http://en.wikipedia.org/wiki/Object-relational_impedance_mis... MongoDB is just ODB, and MySQL is just RDB. Besides, postgres is the real future!

Not sure what Wu-Tang has to do with this, but.... Seriously though, is Mongo an ODB, or a document oriented database? ODBs/OODBs imply a much different use-case and functionality, and I think we ought not conflate the two.

Mongo is not an ODB in the traditional ODB sense. Mongo is just a document (or blob) database. ODB supports relationship, link traversal, inheritance, etc. Basically the whole shebang of the OO notions in a database.

Re: Things I wish I knew about MongoDB a year ago

#49

Post by amalag »

joevandyk wrote: post #27
thibaut_barrere wrote: post #13

Earlier quoted context omitted.

MongoDB kicks ass in the following situations (real projects I did as a freelancer): - dealing with semi-structured input (forms with some variability) and storing as a document, all while being able to query across the data - used as a store to provide very flexible ETL jobs (with ability to upsert, filter/query, geonear etc) For those situations, I would definitely use MongoDB again. As a RDBMS replacement, I would…

fwiw, postgresql 9.2 supports a json datatype. you can efficiently access/query json fields using plv8 ( http://code.google.com/p/plv8js/ ). so you could have: create table form_results ( id serial primary key, data json ); http://pgeu-plv8.herokuapp.com/ has more information.

I don't quite understand how the transition happened from no-json support to json support in those slides. How did the plv8js do this searching on fields?

Re: Things I wish I knew about MongoDB a year ago

#50

Post by ismarc »

jvehent wrote: post #45
joevandyk wrote: post #27

Earlier quoted context omitted.

fwiw, postgresql 9.2 supports a json datatype. you can efficiently access/query json fields using plv8 ( http://code.google.com/p/plv8js/ ). so you could have: create table form_results ( id serial primary key, data json ); http://pgeu-plv8.herokuapp.com/ has more information.

It's just a JSON syntax validator. You can't index on part of the json, postgres treats it as a string. You can apply full text search on it, but that doesn't tell you if you're matching on a key or a value.

In postgres, you can index on a stored procedure, so you can use a simple stored procedure written in JavaScript to look up by key and return values, etc. Example available at http://people.planetpostgresql.org/andrew/index.php?/archive...
Post reply on HN