# Apache-Mongrel-Rails-SQLite-Multithreading **URL:** \ **Category:** Rails\ **Created:** [February 26, 2007, 5:50am UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808 "2007-02-26T05:50:47Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 5:50am UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/1 "2007-02-26T05:50:47Z")
Hi. I have read that using SQLite for a high volume web site is not advised because of the single-threaded, one-at-a-time nature of SQLite and Rails. They say that it is better to use a multithreaded database server based database such as MySQL, PostgreSQL, etc. I assume that this is to be able to “concurrently” handle large number of database access requests. However there is a new configuration that uses Apache 2.x (with mod\_load\_balancer) to forward requests to a cluster of Mongrels (a Ruby web server for rails), which then accesses the database through the Rails application. My understanding is that Apache 2.x is multithreaded. My question is…if Apache is going to handle the multithreadedness of the applications, why does the database also have to be multithreaded for high-volume applications? For example, suppose that I have an application with Apache 2.x, mod\_load\_balancer, Mongrel, Rails and my appilcation and using an SQLite database, what is the compelling reason to go for this versus MySQL, given that Apache 2.x can handle multiple web requests at the same time? For the question above, if there is no good multithreading-related reason to go to a server-based database, then will I still get multthreadedness in some degree if I choose to have Apache forward requests to only one Mongrel/Rails/myApp/SQLite cluster? Curiously, Jay ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 4:54pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/2 "2007-02-26T16:54:07Z")
Jay, If any component of the entire application stack is single threaded, it will become a bottleneck. In the architecture you’ve proposed, Apache could handle multiple requests simultaneously & then would pass them onto mod\_load\_balancer, which in turn passes the request onto a given instance of Mongrel. When Mongrel then begins to execute it’s request, it asks SQLite. If SQLite is singlethreaded, then it must complete it’s query before another mongrel instance can query it. This means the multi-threaded nature of Apache & mod\_load\_balancer is effectively negated as you are database bound. Although your Apache aspect is multithreaded & you may see some improvements in capacity for any static content (served by Apache) and any rails requests which don’t hit the database, it won’t magically improve the performance of database-bound requests. Keep in mind that Mongrel is also single threaded, thus the reason for mod\_load\_balancer, which hands off requests to multiple instances of Mongrel (sort of like how Apache 1.3 worked with multiple processes). If you use a single instance of Mongrel behind mod\_load\_balancer, it is providing zero benefit & perhaps due to the load-balancer overhead might reduce your capacity. Your final question sounded like that was what you intended. Niels ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 5:14pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/3 "2007-02-26T17:14:18Z")
Niels Meersschaert wrote the following on 26.02.2007 16:52 : > Keep in mind that Mongrel is also single threaded, Just to be sure. I believed that Mongrel was multi-threaded, but that the rails interface was protected by a mutex or the equivalent? Which means that you could serve multiple requests by a single Mongrel process as long as they don’t involve Rails (static files, Merb, the Mongrel upload plugin and so on…). In fact multiple uploads handled by a single Mongrel process could matter to me. Lionel ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 5:20pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/4 "2007-02-26T17:20:19Z")
Hi Niels. Your argument makes sense. However, let me extend your argument. I know that MySQL stores data in one file per table, as opposed to SQLite which uses one file for the whole database. With MySQL, even though the database server is multithreaded, access to the database file is “single-threaded” just as with SQLite…i.e. In both cases, we are file-bound (assuming that the query has multiple requests that amount to doing a fopen/fread/fclose on the same file), although I would expect better concurrent performance from MySQL for multiple queries on different tables. I guess the core of my argument is that given that we are file-bound in both cases, what does two cascading multithreading systems (Apache and MySQL database server) buy us versus only one (Apache)? You guessed correctly at the end which is that I would like to use Apache to front-end my single threaded Mongrel/Rails/SQLite application. The main motivation for this is to use its free multithreading from Apache. Cheers, Jay ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 8:37pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/5 "2007-02-26T20:37:51Z")
Hi Lionel. I think you have best described the core of the problem, and that is the one regarding the granularity of locking. It seems to me that both MySQL and SQLite use file-level locking, but MySQL uses one file per table instead of one file for the whole database as SQLite does. However, the core question remains (slightly modified). If I have a web application that needs to be multithreaded to support concurrent access to the database file (whether in MySQL or SQLite), what is the advantage of having two cascading multithreaded entities (Apache and the MySQL database server) in front of the lock-bound database file, versus having only one multithreaded entity (Apache) fronting the SQLite database file? Curiously, Jay P.S. My understanding is that SQLite supports one concurrent writer and multiple concurrent readers. On Feb 26, 11:41 am, Lionel B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 5:42pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/6 "2007-02-26T17:42:21Z")
Jay Godse wrote the following on 26.02.2007 17:17 : > queries on different tables. > > I guess the core of my argument is that given that we are file-bound > in both cases, what does two cascading multithreading systems (Apache > and MySQL database server) buy us versus only one (Apache)? The problem is not exactly the threading in itself but the amount of locking done on the database. The more fine-grained locking your database system can do, the less it will get in the way of multiple clients accessing the database for different needs (which aren’t actually slowed down by disks but by locks waiting for clients to finish a transaction which might imply heavy processing on the clients to be released). SQLite was originally designed with a single client in mind, no concurrent access whatsoever. It introduced multiple simultaneous clients along the way but it probably as a long catch-up to do if it wants to rival full-fledged RDBMS like MySQL or PostgreSQL. I don’t think SQLite tries to address multiple clients performance needs so I wouldn’t hold my breath… I believe PostgreSQL to have theoritically the best concurrent access involving writes and transactions (if compared to InnoDB, MyISAM is another matter). Unfortunately benchmarks are lacking to verify it, if someone knows of transactional benchmarks comparing MySQL with InnoDB and PostgreSQL, I’d like to know. Lionel. ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 26, 2007, 8:46pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/7 "2007-02-26T20:46:28Z")
At least with InnoDB, Mysql has row level locking. All of your your actual data is in just a handful of files, not split by table (in mysql/data/ibdata1, mysql/data/ibdata2 etc…). No file level locking going around there. SQL lite can have multiple concurrent readers or 1 concurrent writer, not both. If anyone, anywhere is writing a change to the database, then absolutely everyone else has to wait for that update to complete before being able to do anything at all. For most uses that is not an acceptable situation. Fred ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 27, 2007, 9:49am UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/8 "2007-02-27T09:49:17Z")
On 2/26/07, Lionel B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I believe PostgreSQL to have theoritically the best concurrent access > involving writes and transactions (if compared to InnoDB, MyISAM is > another matter). Unfortunately benchmarks are lacking to verify it, if > someone knows of transactional benchmarks comparing MySQL with InnoDB > and PostgreSQL, I’d like to know. Not sure how/what these guys are testing, but their graphs do seem to back your view: > **[Database test: dual Intel Xeon 5160](https://tweakers.net/reviews/657/6/)** > **[Database test: Sun UltraSparc T1 vs. AMD Opteron](https://tweakers.net/reviews/649/7/)** But don’t pick postgres just because it’s faster. Use it because it’s standards-compliant and well-behaved, unlike mysql. Isak ---
**Author:** ![Jay\_Godse](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7ba0ec/32.png) [@Jay\_Godse](https://www.ruby-forum.com/u/Jay_Godse)\ **Post date:** [February 27, 2007, 8:50pm UTC](https://www.ruby-forum.com/t/apache-mongrel-rails-sqlite-multithreading/86808/9 "2007-02-27T20:50:24Z")
Isak H. wrote the following on 27.02.2007 09:48 : > back your view: > [Database test: dual Intel Xeon 5160 - Overview - Engelstalig - Tweakers](http://tweakers.net/reviews/657/6) > [Database test: Sun UltraSparc T1 vs. AMD Opteron - MySQL vs. PostgreSQL - Engelstalig - Tweakers](http://tweakers.net/reviews/649/7) Good, real-case scenarios with recent versions! They even say that their SQL code is initially tuned for MySQL and there’s probably still room for improvements… > But don’t pick postgres just because it’s faster. Use it because it’s > standards-compliant and well-behaved, unlike mysql. That was my initial motivation for choosing PostgreSQL, trust me I know a few of MySQL’s liberties with SQL and limitations from experience 🙂 But I wanted to have an early peak (before performing benchmarks myself on final code) at the concurrent access behaviour. Thank you very much. Lionel.