6 ms·

Don't Bet on Moore Saving Your Ass

82 points by prakash 18y ago

nihilocrat 18y ago
Does anyone know if PostgreSQL has this similar multicore bottleneck?
- mdasen 18y ago
  PostgreSQL is much better at using multiple cores, but it doesn't matter (at least not for web applications). Web applications don't have a problem handling one person. They have a problem handling 1,000 people who all want to load a page at the same time. That means that you're not worried about using all your server resources for one query. You're going to have 1,000 queries and so 250 go to each core in a quad-core box and you don't care that MySQL (InnoDB really) doesn't do the multi-core thing because it's not like PostgreSQL would benefit from it since it's just easier to do different queries using a different core. Multi-core capabilities could help when you are running fewer concurrent queries than you have processor cores. However, once you get to 4-8 concurrent users, you don't need to worry about it so much because you'll saturate all the cores through the different queries and when you're below 4-8 concurrent users you don't need to worry about it because it's easy to serve few users. Now, for data warehousing and other applications, multi-core capabilities can be the difference between a query taking 1 hour and a query taking 4 hours. But that's not a web application. In fact, using MySQL for data warehousing is just a bad idea. The author is totally right that you shouldn't just expect technology to save you (and I personally think DHH is taking the "wait until it is a problem. if becomes a problem and new hardware can solve it, do that. if not, then deal with it" approach rather than simply expecting a solution). However, web applications are about running many things at once, not running one big thing. P.S. Databases usually aren't CPU constrained. It's almost always memory or disk that slows you down. Spend the money on more RAM or better disks and don't worry about the CPU so much. P.P.S. Both MySQL and PostgreSQL are wonderful databases for web applications so let's not turn this into some silly flame war, please?
  - Retric 18y ago
    Your ignoring the issue of locking, which can effectively transform your multi core CPU in a single core. Secondly databases can be limited depending on what your asking them to do not just what type of work your doing. IMO the largest advantage to multi core CPU's is handing a longer list of requests the the disk controller so it can better optimize the the head's path.
  - sounddust 18y ago
    PostgreSQL is much better at using multiple cores, and it absolutely does matter for web applications. When you have 1,000 people who all want to load a page at the same time, you're only going to hit the database once for that. What you will have instead is 5,000 people who want to go to 1,000 different pages, some of them updating data and some of them retrieving it, and you will have 1,000 different queries that are either selects or updates. Now, PostgreSQL was designed from the start to be robust enough to handle this type of concurrency - to allow the minimum amount of data to be locked while updating, to free the selects from being blocked by those writes. As a result of being built on such a solid foundation, it has been easy to optimize over the years, and has supported the emergence of commmon multi-core computing quite well. MySQL, on the other hand, was designed to return queries extremely quickly, with as little getting in the way of doing so as possible. Unfortunately, their model did not scale as well. When you have 500 reads and 1 write, and you lock the entire table for that write, it's not a big deal because the write takes no time and you're unblocked again. But when you have an array of hundreds of simultaneous reads and writes, it becomes a mess if you don't have fine-grained locking capabilities. That having been said, MySQL is progressing as well. But I think (not trying to start a flame war) that PostgreSQL did things slow and right in the beginning and it's paying off pretty well. Finally, I disagree that databases are not CPU constrained. Any website with decent traffic will have the database entirely cached in RAM at all times, with the only disk activity being the journaling.
    - mdasen 18y ago
      PostgreSQL was designed "correct" from the start. However, MySQL does many of the same things today. You start by saying you'll have 5,000 people who want 1,000 different pages with some updates, some selects, etc. Well, once you have more queries than cores, the benefit of splitting work over multiple cores is gone since none of the queries can logically use even a whole single core given the level of concurrency. You go on to say that PostgreSQL was designed to eliminate unnecessary locking so that selects wouldn't be blocked. MySQL's MyISAM database doesn't support this, that is correct. However, InnoDB does support the same MVCC model that PostgreSQL uses and likewise eliminates the locking issue. Your argument rests on MySQL locking an entire table to do a write: "When you have 500 reads and 1 write, and you lock the entire table for that write, it's not a big deal. . . But when you have an array of hundreds of simultaneous reads and writes, it becomes a mess if you don't have fine-grained locking capabilities." A great article on this problem is here: http://www.onlamp.com/pub/a/onlamp/2001/05/25/postgresql_mvcc.html http://www.onlamp.com/pub/a/onlamp/2001/05/25/postgresql_mvc.... It's great that PostgreSQL supports that, but MySQL supports it too today (http://wiki.oracle.com/page/InnoDB?t=anon http://wiki.oracle.com/page/InnoDB?t=anon). There are plenty of things that one can say are issues between the two. MySQL's inferior query planner. The fact that PostgreSQL can suggest indexes based on query history. PostgreSQL's weak replication (Slony-I's communication costs grow quadratically, yuck!). MySQL's acceptance of February 31st as a real date. MySQL's poor subquery optimization. PostgreSQL's more limited data partitioning. They aren't equal in all ways and PostgreSQL is a wonderful database, but saying that MySQL needs to lock a table to do a write is just wrong in a very partisan manner. I've never really understood such partisanship. Knowing the strengths and weaknesses of multiple products makes you aware of what is good for a project and what isn't. Even better, once you're using one of them, you know what to do and what to avoid with it. Not confronting the reality of how alternative systems work just means that the chance of picking the best system is more luck than information. For what it's worth, I use PostgreSQL in my personal projects. It's great. However, it's also important to understand that MySQL of 2008 is not MySQL of 2001. It's come a long way in the "correctness" camp and the old arguments about Multi-Version Concurrency Control don't apply anymore. Oh, and from Power PostgreSQL, Disks > RAM > CPU (http://www.powerpostgresql.com/PerfList http://www.powerpostgresql.com/PerfList).
- andrewf 18y ago
  Sun has previously demonstrated Postgres scaling well on their 32-way (8 cores x 4 threads/core) hardware. http://it.toolbox.com/blogs/database-soup/postgresql-publishes-first-real-benchmark-17470 http://it.toolbox.com/blogs/database-soup/postgresql-publish...
russell 18y ago
I think all kinds of components and applications are going to hit the wall. The python interpreter doesn't even support multiple real threads let alone multiple cores. Programmers don't know how to write the code. Here is an article musing about the problems in Java: http://www.devwebsphere.com/devwebsphere/2006/11/multicore_may_b.html http://www.devwebsphere.com/devwebsphere/2006/11/multicore_m... Do we all need to learn erlang?
- ramchip 18y ago
  Clojure has put a major emphasis on fixing multithreading for Java - I don't know about garbage collection and problems with the JVM itself, though.
- deleted 18y ago
  [deleted]
- stcredzero 18y ago
  I'd rather have some sort of support for multiple cores without real threads. Stackless seems like a good alternative to Erlang. Take the two statements above as standalone.
  - russell 18y ago
    I agree that Stackless is better. Threads are very heavyweight. The problem is that the underlying C interpreter works on only one core. If Stackless can work with multiple interpreters then it may be the greatest thing since sliced bread. I haven't been following it closely enough to say for sure.
    - stcredzero 18y ago
      All you have to do is build a mechanism that distributes threads between interpreter processes then just spawn an interpreter for each core. For many applications, that's all you need.
  - likpok 18y ago
    I seem to recall a benchmark that showed Erlang as much faster than Stackless (for an admittedly relatively arbitrary problem).
mattmaroon 18y ago
A website can grow a lot faster than Moore's law would account for.
- raghus 18y ago
  Zuckerberg's Law?
- mattmaroon 18y ago
  Though I suppose Moore's law has a head start, and grows faster than the overall population. At some point, if it continued indefinitely, databases would become powerful enough to serve 100% of the human population for a typical app on a single server.
  - icey 18y ago
    All this Moore's law talk is driving me insane. Improvements in performance are only a side effect of Moore's law. Moore's law only states that the density of transistors on a chip will double every 2 years. This will fail because of the Zeno's paradox-like effect of limited miniaturization. At some point, transistors will have to become molecule size, and then atomic, at which point it should be theoretically impossible to get any smaller. (Sorry for the derailment, and yes, I also go bonkers over centrifugal vs centripetal.) Finally, DHH may be amazing at writing frameworks, but he is just about the absolute last person I would trust with anything that resembled math.
    - skenney26 18y ago
      The issue isn't about math. The opinion of anyone who's maintaining a profitable business should be given extra attention.
      - mattmaroon 18y ago
        I don't agree with that. Running a profitable business doesn't automatically make your opinions on everything unusually worthy of consideration.
stcredzero 18y ago
One thing to make note of: if you are in a space where you have massive concurrency, the right kind of hardware can help you out. There was a time in the mid 90's when mainframes with CPUs we would regard as quaintly slow could still achieve I/O throughput that could dwarf the throughput of a PC with an order of magnitude faster CPU.
axod 18y ago
Quite a few webapps just shouldn't be using a db for most things. It's lazy programming.
- bmj 18y ago
  Care to expand on this?
- mixmax 18y ago
  What then? Asking out of curiosity/ignorance, not trolling
  - mynameishere 18y ago
    I think this website (hacker news) just uses persisted hash tables. I'm not sure why he thinks databases indicate "lazy programming" though.
    - axod 18y ago
      It's really easy to just throw everything in a db, and then start worrying when you scale. It takes more programming to think how best to organize things - what stuff should be in memory? How best to store it in ram for performance/size? What should be on the disk as flat files? What needs to be in a db? Should parts of the db be cached in ram and just used for writes etc. Also does everything need to be in a db? Or are some things better dealt with by just passing messages around, queuing them up if needed etc.
      - ars 18y ago
        > Should parts of the db be cached in ram and just used for writes etc. You are working way too hard. Let the OS figure out what needs to be in ram - it does it automatically anyway, and it does a better job that you an since it's caches what actually used, and not what you think should be used. You should not use flat files for web apps - they don't handle concurrency very well. > Also does everything need to be in a db? Or are some things better dealt with by just passing messages around, queuing them up if needed etc. Message passing, and db are not interchangeable, so that's a false question.
ruby_roo 18y ago
I'm very interested in book recommendations for scaling websites from hundreds of users to millions of users. I'm interested in both database and web server configurations as well as hardware details, and war stories from the trenches. Also, I'd like to know if there bits of wisdom I can incorporate into my 1.0 codebase to make scaling easier should I be fortunate enough to have that problem. Ideas from the HN crowd?
- alecthomas 18y ago
  Reading articles and watching videos from the engineering teams of big sites is interesting, though not always easily applicable. For example, the Facebook Engineering Blog (http://www.facebook.com/eblog http://www.facebook.com/eblog) or Google Tech Talks (http://au.youtube.com/results?search_query=google+tech+talk+scaling&search_type=&aq=f http://au.youtube.com/results?search_query=google+tech+talk+...).
- mdasen 18y ago
  http://oreilly.com/catalog/9780596102357/ http://oreilly.com/catalog/9780596102357/ Building Scalable Websites by the Flickr guy.
- joshwa 18y ago
  http://highscalability.com/ http://highscalability.com/
likpok 18y ago
One other thing: Moore's law is fundamentally limited. Remember that the limit of the exponential function as t-> infinity is infinity. This should be enough to show you that at some point, Moore's law will end. It is less important right now (there is still some development going, and new paradigms in the far future) , but the world is not limitless.
zandorg 18y ago
I only just starting using MySQL to store tables of around 100,000 entries. But MySQL would take literally > 30 seconds (sometimes taking minutes) for a query that PostgreSQL (which I installed after it) can handle in 10 seconds. It seems like MySQL is therefore dreck. I can't see any reason not to use PostgreSQL.
- zmimon 18y ago
  There's something terribly horribly wrong with either your database setup or your queries. 100,000 entries is miniscule. Do you have indexes on the join columns in your queries? (But do use Postgres, it's better than MySQL for most cases!)
  - zandorg 18y ago
    I learned SQL at University, but that was 5 years ago so I'm a bit rusty. There's 1 table with a primary key (a string ID), which is used for rows with duplicate ID's, so in theory MySQL should be quick with it. Thanks for the info, I'll have to dig further, but at least now I know it should be fast even in MySQL.
    - thamer 18y ago
      Try using EXPLAIN on your queries. That will give you a lot of info on how many rows are examined by your SELECT statements.

82 points by prakash 18y ago

nihilocrat 18y ago

Does anyone know if PostgreSQL has this similar multicore bottleneck?

mdasen 18y ago
PostgreSQL is much better at using multiple cores, but it doesn't matter (at least not for web applications). Web applications don't have a problem handling one person. They have a problem handling 1,000 people who all want to load a page at the same time. That means that you're not worried about using all your server resources for one query. You're going to have 1,000 queries and so 250 go to each core in a quad-core box and you don't care that MySQL (InnoDB really) doesn't do the multi-core thing because it's not like PostgreSQL would benefit from it since it's just easier to do different queries using a different core. Multi-core capabilities could help when you are running fewer concurrent queries than you have processor cores. However, once you get to 4-8 concurrent users, you don't need to worry about it so much because you'll saturate all the cores through the different queries and when you're below 4-8 concurrent users you don't need to worry about it because it's easy to serve few users. Now, for data warehousing and other applications, multi-core capabilities can be the difference between a query taking 1 hour and a query taking 4 hours. But that's not a web application. In fact, using MySQL for data warehousing is just a bad idea. The author is totally right that you shouldn't just expect technology to save you (and I personally think DHH is taking the "wait until it is a problem. if becomes a problem and new hardware can solve it, do that. if not, then deal with it" approach rather than simply expecting a solution). However, web applications are about running many things at once, not running one big thing. P.S. Databases usually aren't CPU constrained. It's almost always memory or disk that slows you down. Spend the money on more RAM or better disks and don't worry about the CPU so much. P.P.S. Both MySQL and PostgreSQL are wonderful databases for web applications so let's not turn this into some silly flame war, please?
- Retric 18y ago
  Your ignoring the issue of locking, which can effectively transform your multi core CPU in a single core. Secondly databases can be limited depending on what your asking them to do not just what type of work your doing. IMO the largest advantage to multi core CPU's is handing a longer list of requests the the disk controller so it can better optimize the the head's path.
- sounddust 18y ago
  PostgreSQL is much better at using multiple cores, and it absolutely does matter for web applications. When you have 1,000 people who all want to load a page at the same time, you're only going to hit the database once for that. What you will have instead is 5,000 people who want to go to 1,000 different pages, some of them updating data and some of them retrieving it, and you will have 1,000 different queries that are either selects or updates. Now, PostgreSQL was designed from the start to be robust enough to handle this type of concurrency - to allow the minimum amount of data to be locked while updating, to free the selects from being blocked by those writes. As a result of being built on such a solid foundation, it has been easy to optimize over the years, and has supported the emergence of commmon multi-core computing quite well. MySQL, on the other hand, was designed to return queries extremely quickly, with as little getting in the way of doing so as possible. Unfortunately, their model did not scale as well. When you have 500 reads and 1 write, and you lock the entire table for that write, it's not a big deal because the write takes no time and you're unblocked again. But when you have an array of hundreds of simultaneous reads and writes, it becomes a mess if you don't have fine-grained locking capabilities. That having been said, MySQL is progressing as well. But I think (not trying to start a flame war) that PostgreSQL did things slow and right in the beginning and it's paying off pretty well. Finally, I disagree that databases are not CPU constrained. Any website with decent traffic will have the database entirely cached in RAM at all times, with the only disk activity being the journaling.
  - mdasen 18y ago
    PostgreSQL was designed "correct" from the start. However, MySQL does many of the same things today. You start by saying you'll have 5,000 people who want 1,000 different pages with some updates, some selects, etc. Well, once you have more queries than cores, the benefit of splitting work over multiple cores is gone since none of the queries can logically use even a whole single core given the level of concurrency. You go on to say that PostgreSQL was designed to eliminate unnecessary locking so that selects wouldn't be blocked. MySQL's MyISAM database doesn't support this, that is correct. However, InnoDB does support the same MVCC model that PostgreSQL uses and likewise eliminates the locking issue. Your argument rests on MySQL locking an entire table to do a write: "When you have 500 reads and 1 write, and you lock the entire table for that write, it's not a big deal. . . But when you have an array of hundreds of simultaneous reads and writes, it becomes a mess if you don't have fine-grained locking capabilities." A great article on this problem is here: http://www.onlamp.com/pub/a/onlamp/2001/05/25/postgresql_mvcc.html http://www.onlamp.com/pub/a/onlamp/2001/05/25/postgresql_mvc.... It's great that PostgreSQL supports that, but MySQL supports it too today (http://wiki.oracle.com/page/InnoDB?t=anon http://wiki.oracle.com/page/InnoDB?t=anon). There are plenty of things that one can say are issues between the two. MySQL's inferior query planner. The fact that PostgreSQL can suggest indexes based on query history. PostgreSQL's weak replication (Slony-I's communication costs grow quadratically, yuck!). MySQL's acceptance of February 31st as a real date. MySQL's poor subquery optimization. PostgreSQL's more limited data partitioning. They aren't equal in all ways and PostgreSQL is a wonderful database, but saying that MySQL needs to lock a table to do a write is just wrong in a very partisan manner. I've never really understood such partisanship. Knowing the strengths and weaknesses of multiple products makes you aware of what is good for a project and what isn't. Even better, once you're using one of them, you know what to do and what to avoid with it. Not confronting the reality of how alternative systems work just means that the chance of picking the best system is more luck than information. For what it's worth, I use PostgreSQL in my personal projects. It's great. However, it's also important to understand that MySQL of 2008 is not MySQL of 2001. It's come a long way in the "correctness" camp and the old arguments about Multi-Version Concurrency Control don't apply anymore. Oh, and from Power PostgreSQL, Disks > RAM > CPU (http://www.powerpostgresql.com/PerfList http://www.powerpostgresql.com/PerfList).
andrewf 18y ago
Sun has previously demonstrated Postgres scaling well on their 32-way (8 cores x 4 threads/core) hardware. http://it.toolbox.com/blogs/database-soup/postgresql-publishes-first-real-benchmark-17470 http://it.toolbox.com/blogs/database-soup/postgresql-publish...

russell 18y ago

I think all kinds of components and applications are going to hit the wall. The python interpreter doesn't even support multiple real threads let alone multiple cores. Programmers don't know how to write the code. Here is an article musing about the problems in Java: http://www.devwebsphere.com/devwebsphere/2006/11/multicore_may_b.html http://www.devwebsphere.com/devwebsphere/2006/11/multicore_m... Do we all need to learn erlang?

ramchip 18y ago
Clojure has put a major emphasis on fixing multithreading for Java - I don't know about garbage collection and problems with the JVM itself, though.
deleted 18y ago
[deleted]
stcredzero 18y ago
I'd rather have some sort of support for multiple cores without real threads. Stackless seems like a good alternative to Erlang. Take the two statements above as standalone.
- russell 18y ago
  I agree that Stackless is better. Threads are very heavyweight. The problem is that the underlying C interpreter works on only one core. If Stackless can work with multiple interpreters then it may be the greatest thing since sliced bread. I haven't been following it closely enough to say for sure.
  - stcredzero 18y ago
    All you have to do is build a mechanism that distributes threads between interpreter processes then just spawn an interpreter for each core. For many applications, that's all you need.
- likpok 18y ago
  I seem to recall a benchmark that showed Erlang as much faster than Stackless (for an admittedly relatively arbitrary problem).

mattmaroon 18y ago

A website can grow a lot faster than Moore's law would account for.

raghus 18y ago
Zuckerberg's Law?
mattmaroon 18y ago
Though I suppose Moore's law has a head start, and grows faster than the overall population. At some point, if it continued indefinitely, databases would become powerful enough to serve 100% of the human population for a typical app on a single server.
- icey 18y ago
  All this Moore's law talk is driving me insane. Improvements in performance are only a side effect of Moore's law. Moore's law only states that the density of transistors on a chip will double every 2 years. This will fail because of the Zeno's paradox-like effect of limited miniaturization. At some point, transistors will have to become molecule size, and then atomic, at which point it should be theoretically impossible to get any smaller. (Sorry for the derailment, and yes, I also go bonkers over centrifugal vs centripetal.) Finally, DHH may be amazing at writing frameworks, but he is just about the absolute last person I would trust with anything that resembled math.
  - skenney26 18y ago
    The issue isn't about math. The opinion of anyone who's maintaining a profitable business should be given extra attention.
    - mattmaroon 18y ago
      I don't agree with that. Running a profitable business doesn't automatically make your opinions on everything unusually worthy of consideration.

stcredzero 18y ago

One thing to make note of: if you are in a space where you have massive concurrency, the right kind of hardware can help you out. There was a time in the mid 90's when mainframes with CPUs we would regard as quaintly slow could still achieve I/O throughput that could dwarf the throughput of a PC with an order of magnitude faster CPU.

axod 18y ago

Quite a few webapps just shouldn't be using a db for most things. It's lazy programming.

bmj 18y ago
Care to expand on this?
mixmax 18y ago
What then? Asking out of curiosity/ignorance, not trolling
- mynameishere 18y ago
  I think this website (hacker news) just uses persisted hash tables. I'm not sure why he thinks databases indicate "lazy programming" though.
  - axod 18y ago
    It's really easy to just throw everything in a db, and then start worrying when you scale. It takes more programming to think how best to organize things - what stuff should be in memory? How best to store it in ram for performance/size? What should be on the disk as flat files? What needs to be in a db? Should parts of the db be cached in ram and just used for writes etc. Also does everything need to be in a db? Or are some things better dealt with by just passing messages around, queuing them up if needed etc.
    - ars 18y ago
      > Should parts of the db be cached in ram and just used for writes etc. You are working way too hard. Let the OS figure out what needs to be in ram - it does it automatically anyway, and it does a better job that you an since it's caches what actually used, and not what you think should be used. You should not use flat files for web apps - they don't handle concurrency very well. > Also does everything need to be in a db? Or are some things better dealt with by just passing messages around, queuing them up if needed etc. Message passing, and db are not interchangeable, so that's a false question.

ruby_roo 18y ago

I'm very interested in book recommendations for scaling websites from hundreds of users to millions of users. I'm interested in both database and web server configurations as well as hardware details, and war stories from the trenches. Also, I'd like to know if there bits of wisdom I can incorporate into my 1.0 codebase to make scaling easier should I be fortunate enough to have that problem. Ideas from the HN crowd?

alecthomas 18y ago
Reading articles and watching videos from the engineering teams of big sites is interesting, though not always easily applicable. For example, the Facebook Engineering Blog (http://www.facebook.com/eblog http://www.facebook.com/eblog) or Google Tech Talks (http://au.youtube.com/results?search_query=google+tech+talk+scaling&search_type=&aq=f http://au.youtube.com/results?search_query=google+tech+talk+...).
mdasen 18y ago
http://oreilly.com/catalog/9780596102357/ http://oreilly.com/catalog/9780596102357/ Building Scalable Websites by the Flickr guy.
joshwa 18y ago
http://highscalability.com/ http://highscalability.com/

likpok 18y ago

One other thing: Moore's law is fundamentally limited. Remember that the limit of the exponential function as t-> infinity is infinity. This should be enough to show you that at some point, Moore's law will end. It is less important right now (there is still some development going, and new paradigms in the far future) , but the world is not limitless.

zandorg 18y ago

I only just starting using MySQL to store tables of around 100,000 entries. But MySQL would take literally > 30 seconds (sometimes taking minutes) for a query that PostgreSQL (which I installed after it) can handle in 10 seconds. It seems like MySQL is therefore dreck. I can't see any reason not to use PostgreSQL.

zmimon 18y ago
There's something terribly horribly wrong with either your database setup or your queries. 100,000 entries is miniscule. Do you have indexes on the join columns in your queries? (But do use Postgres, it's better than MySQL for most cases!)
- zandorg 18y ago
  I learned SQL at University, but that was 5 years ago so I'm a bit rusty. There's 1 table with a primary key (a string ID), which is used for rows with duplicate ID's, so in theory MySQL should be quick with it. Thanks for the info, I'll have to dig further, but at least now I know it should be fast even in MySQL.
  - thamer 18y ago
    Try using EXPLAIN on your queries. That will give you a lot of info on how many rows are examined by your SELECT statements.