MongoDB's Write Lock • Hacker News Board

Re: MongoDB's Write Lock

#11

Post by nknight » Sat, Dec 31, 2011, 11:19 PM UTC

DenisM wrote: post #7

> MongoDB, as some of you may know, has a process-wide write lock. I've never taken time to see what MogoDB db is, but thanks to this opening sentence, now I know everything I ever wanted to know about this system. Having worked for 13 years on database system design I am pretty confident that a system not designed with concurrency in mind cannot be retrofitted with any decent concurrency later. Thank you Rick for sa…

Why is it all the "experienced" database people I encounter remind me of flat earthers? Are you really so hung up on yourselves that you'll watch the entire industry pass you by rather than admit the traditional models might not always be the best models for every situation?

Re: MongoDB's Write Lock

#12

Post by ketralnis » Sat, Dec 31, 2011, 11:25 PM UTC

xxqs wrote: post #4

Why is everyone paying so much attention to MongoDB? It has been criticized a lot for its design and implementation problems, but still for some reason it's so popular. To name a few, * word-unaligned memory structures, which leads to incompatibility with virtually any non-x86 CPU architecture * explicitly little-endian processing in the server, so there is no way to run the original code on any big-endian CPU archit…

Yeah, how dare people like what you don't like?

> It has been criticized a lot [...] but still for some reason it's so popular

Since you provide no data or sources for "criticized a lot" it's no surprise that you don't provide the same for "so popular". I assume you mean "I've seen some headlines on Hacker News about it".

> incompatibility with virtually any non-x86 CPU architecture [...] no way to run the original code on any big-endian CPU architecture

Huh. Maybe that's only a problem for people on non-x86 CPUs then?

Look I'm really not a fan of Mongo but "It has been criticized a lot [...] but still for some reason it's so popular" describes every technology ever. Get over it.

Re: MongoDB's Write Lock

#13

Post by milkshakes » Sat, Dec 31, 2011, 11:25 PM UTC

DenisM wrote: post #7

> MongoDB, as some of you may know, has a process-wide write lock. I've never taken time to see what MogoDB db is, but thanks to this opening sentence, now I know everything I ever wanted to know about this system. Having worked for 13 years on database system design I am pretty confident that a system not designed with concurrency in mind cannot be retrofitted with any decent concurrency later. Thank you Rick for sa…

without explicitly defending this decision*, i'd like to point out that mongodb was never intended to be deployed as a single node living on a single machine.

it was designed with concurrency in mind, the concurrency you're looking for comes in the form of sharding and replica sets though.

edit: meh, got bored, decided to defend it: http://news.ycombinator.com/item?id=3412283

Re: MongoDB's Write Lock

#14

Post by xxqs » Sat, Dec 31, 2011, 11:28 PM UTC

ketralnis wrote: post #12

xxqs wrote: post #4

Why is everyone paying so much attention to MongoDB? It has been criticized a lot for its design and implementation problems, but still for some reason it's so popular. To name a few, * word-unaligned memory structures, which leads to incompatibility with virtually any non-x86 CPU architecture * explicitly little-endian processing in the server, so there is no way to run the original code on any big-endian CPU archit…

Yeah, how dare people like what you don't like? > It has been criticized a lot [...] but still for some reason it's so popular Since you provide no data or sources for "criticized a lot" it's no surprise that you don't provide the same for "so popular". I assume you mean "I've seen some headlines on Hacker News about it". > incompatibility with virtually any non-x86 CPU architecture [...] no way to run the original c…

> Maybe that's only a problem for people on non-x86 CPUs then?

actually it's a problem for application developers. I cannot rely on a backend system with limitations like these. So I'll have to go back to the RDBMS backend or look for other nosql alternatives, but definitely mongoDB is off my list

Re: MongoDB's Write Lock

#15

Post by nknight » Sat, Dec 31, 2011, 11:32 PM UTC

xxqs wrote: post #14

ketralnis wrote: post #12

Earlier quoted context omitted.

Yeah, how dare people like what you don't like? > It has been criticized a lot [...] but still for some reason it's so popular Since you provide no data or sources for "criticized a lot" it's no surprise that you don't provide the same for "so popular". I assume you mean "I've seen some headlines on Hacker News about it". > incompatibility with virtually any non-x86 CPU architecture [...] no way to run the original c…

> Maybe that's only a problem for people on non-x86 CPUs then? actually it's a problem for application developers. I cannot rely on a backend system with limitations like these. So I'll have to go back to the RDBMS backend or look for other nosql alternatives, but definitely mongoDB is off my list

The world runs on x86. You might have some legacy systems running SPARC or POWER, but those systems are unlikely to reside in MongoDB's target market anyway.

Arguing everyone else should ditch code that happens to not work on your pet architecture is a pretty self-centered worldview.

Re: MongoDB's Write Lock

#16

Post by DenisM » Sat, Dec 31, 2011, 11:39 PM UTC

old-gregg wrote: post #10

DenisM wrote: post #7

> MongoDB, as some of you may know, has a process-wide write lock. I've never taken time to see what MogoDB db is, but thanks to this opening sentence, now I know everything I ever wanted to know about this system. Having worked for 13 years on database system design I am pretty confident that a system not designed with concurrency in mind cannot be retrofitted with any decent concurrency later. Thank you Rick for sa…

You sound like a "database system design" is just one specific thing that has a well-defined definition which is known to and agreed on by everyone. Ughh... fine, not arguing. But in that case MongoDB is not a "database system" then. How about I call it a tool that holds your data for you and gives it back later. This tool has certain properties that make it work (or not work) for certain applications. It is just tha…

Sure it might be useful, I just don't think it has longevity in it. In other words it will be surpassed by another system, aiming to solve the same set of problems, but designed with concurrency in mind from the start. MongoDB developers will end up spending all their efforts to retrofit concurrency, and the community of users will simply move on.

Re: MongoDB's Write Lock

#17

Post by xxqs » Sat, Dec 31, 2011, 11:40 PM UTC

nknight wrote: post #15

xxqs wrote: post #14

Earlier quoted context omitted.

> Maybe that's only a problem for people on non-x86 CPUs then? actually it's a problem for application developers. I cannot rely on a backend system with limitations like these. So I'll have to go back to the RDBMS backend or look for other nosql alternatives, but definitely mongoDB is off my list

The world runs on x86. You might have some legacy systems running SPARC or POWER, but those systems are unlikely to reside in MongoDB's target market anyway. Arguing everyone else should ditch code that happens to not work on your pet architecture is a pretty self-centered worldview.

actually the number of ARM processors is growing, and not only in the mobile sector. There have been some efforts to bring ARM architecture into the server market. Also China is building its own MIPS-based supercomputer. Also the SPARC architecture is actually developing, although it's a pity to see it swallowed by Oracle. IBM is still shipping PowerPC servers.

besides, there are huge SPARC-only datacenters still running.

Re: MongoDB's Write Lock

#18

Post by DenisM » Sat, Dec 31, 2011, 11:41 PM UTC

nknight wrote: post #11

DenisM wrote: post #7

> MongoDB, as some of you may know, has a process-wide write lock. I've never taken time to see what MogoDB db is, but thanks to this opening sentence, now I know everything I ever wanted to know about this system. Having worked for 13 years on database system design I am pretty confident that a system not designed with concurrency in mind cannot be retrofitted with any decent concurrency later. Thank you Rick for sa…

Why is it all the "experienced" database people I encounter remind me of flat earthers? Are you really so hung up on yourselves that you'll watch the entire industry pass you by rather than admit the traditional models might not always be the best models for every situation?

If you would kindly refrain from personal attacks, we might have a productive conversation, and hacker news might continue to be a place to have such conversations.

Re: MongoDB's Write Lock

#19

Post by xxqs » Sat, Dec 31, 2011, 11:42 PM UTC

ketralnis wrote: post #12

xxqs wrote: post #4

Why is everyone paying so much attention to MongoDB? It has been criticized a lot for its design and implementation problems, but still for some reason it's so popular. To name a few, * word-unaligned memory structures, which leads to incompatibility with virtually any non-x86 CPU architecture * explicitly little-endian processing in the server, so there is no way to run the original code on any big-endian CPU archit…

Yeah, how dare people like what you don't like? > It has been criticized a lot [...] but still for some reason it's so popular Since you provide no data or sources for "criticized a lot" it's no surprise that you don't provide the same for "so popular". I assume you mean "I've seen some headlines on Hacker News about it". > incompatibility with virtually any non-x86 CPU architecture [...] no way to run the original c…

> Since you provide no data or sources for "criticized a lot"

there have been tons of discussions, also on HN, very easy to google

Re: MongoDB's Write Lock

#20

Post by rogerbinns » Sat, Dec 31, 2011, 11:44 PM UTC

DenisM wrote: post #7

> MongoDB, as some of you may know, has a process-wide write lock. I've never taken time to see what MogoDB db is, but thanks to this opening sentence, now I know everything I ever wanted to know about this system. Having worked for 13 years on database system design I am pretty confident that a system not designed with concurrency in mind cannot be retrofitted with any decent concurrency later. Thank you Rick for sa…

There was a poxy operating system a few years ago. It only ran on one 32 bit architecture, didn't have multi-processing, had limited device support and a rather bizarre set of dev tools. Then they tidied things up a bit. But when they added multi-processing these morons just used a single big kernel lock. What a bunch of idiots. Obviously anyone using that operating system was blind and stupid and there were far better solutions.

That operating system is Linux. It started out very simple and was good enough for many people and then kept evolving. Nowadays the alternatives are mainly footnotes in history.

MongoDB is also simple. Its locking approach does not give wrong answers. Its users are happy. Your assertion that the locking can't evolve is bollocks because you have no clue how the database works. While your statement has many elements of truth for a relational database, it is meaningless for the current generation of schemaless/NoSQL databases. Did you know that MongoDB has auto-sharding and replication, and doesn't need locks for that either?