# ActiveRecord Sqlite Synchronization **URL:** \ **Category:** Rails\ **Created:** [May 5, 2008, 2:47pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682 "2008-05-05T14:47:30Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 2:47pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/1 "2008-05-05T14:47:30Z")
Hey! I’m using ActiveRecord with an SQLite Database. It works great, but has one drawback. SQlite does’nt support multiple connection at one time. Is there a mathod to synchronize ActiveRecord calls over different threads? thx CK ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 3:33pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/2 "2008-05-05T15:33:54Z")
google for activerecord multi threaded I think it has something to do with allow\_concurrency. -R On Mon, May 5, 2008 at 6:47 AM, Christian K. ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 4:39pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/3 "2008-05-05T16:39:49Z")
Roger P. wrote: > google for activerecord multi threaded > I think it has something to do with allow\_concurrency. > -R > > On Mon, May 5, 2008 at 6:47 AM, Christian K. Hmmm doesn’t work form me. I still get a “busy-Exception”. Other options? thx ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 5:18pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/4 "2008-05-05T17:18:31Z")
allow\_concurrency “allows conconcurrency” on the connection (as opposed to the database), so 2 threads can execute on the same connection. If you’re trying to have 2 applications read from the same database (like having a script/runner do database stuff in the background while your server runs), this is simply not possible. Because SQLite effectively uses a flat-file, there is no way to have more than 1 connection to the same database – there is no way for one connection to know what the other is doing so as to avoid concurrent modifications resulting in data corruption. On May 5, 9:39 am, Christian K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 5:56pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/5 "2008-05-05T17:56:55Z")
tekwiz wrote: > allow\_concurrency “allows conconcurrency” on the connection (as > opposed to the database), so 2 threads can execute on the same > connection. If you’re trying to have 2 applications read from the > same database (like having a script/runner do database stuff in the > background while your server runs), this is simply not possible. > Because SQLite effectively uses a flat-file, there is no way to have > more than 1 connection to the same database – there is no way for one > connection to know what the other is doing so as to avoid concurrent > modifications resulting in data corruption. i would need a queuing mechanism, that executes queries fifo. Wouldn’t it be possible to achieve such a behaviour with a mutex, that synchronizes access to activerecord’s save and destroy methods? ck ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 6:02pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/6 "2008-05-05T18:02:49Z")
On 5 May 2008, at 16:56, Christian K. wrote: > > connection to know what the other is doing so as to avoid concurrent > > modifications resulting in data corruption. > > i would need a queuing mechanism, that executes queries fifo. > > Wouldn’t it be possible to achieve such a behaviour with a mutex, that > synchronizes access to activerecord’s save and destroy methods? Not if you’re talking about separate mongrels (or rails instance of any sort). But doesn’t sqlite allow enough concurrency ([File Locking And Concurrency In SQLite Version 3](http://www.sqlite.org/lockingv3.html) ) ? Fred ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 6:38pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/7 "2008-05-05T18:38:08Z")
Yes, your fifo/mutex concept is correct. You just have to ensure that 2 active record instances don’t attempt to play with the database at the same time. On May 5, 11:06 am, Christian K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 6:06pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/8 "2008-05-05T18:06:47Z")
Frederick C. wrote: > On 5 May 2008, at 16:56, Christian K. wrote: > > > > connection to know what the other is doing so as to avoid concurrent > > > modifications resulting in data corruption. > > > > i would need a queuing mechanism, that executes queries fifo. > > > > Wouldn’t it be possible to achieve such a behaviour with a mutex, that > > synchronizes access to activerecord’s save and destroy methods? > > Not if you’re talking about separate mongrels (or rails instance of > any sort). But doesn’t sqlite allow enough concurrency > ([File Locking And Concurrency In SQLite Version 3](http://www.sqlite.org/lockingv3.html) > ) ? > > Fred I have one Ruby Process, that runs two threads. In one of them runs a webrick server, one is a background task. Both threads operate on the same database. I’ve done a quick prototype with a mutex and i seems to work; no more busy exceptions. I still have to dig a bit deeper. ---
**Author:** ![sealedsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e68b1a/32.png) [@sealedsun](https://www.ruby-forum.com/u/sealedsun)\ **Post date:** [May 5, 2008, 6:42pm UTC](https://www.ruby-forum.com/t/activerecord-sqlite-synchronization/136682/9 "2008-05-05T18:42:17Z")
You are correct that SQLite3 does provide “enough” concurrency; however, the active record decides to pitch a hissy-fit, throwing exceptions, when it encounters a locked db rather than waiting and trying again for a certain period. On May 5, 11:01 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)