# Postgres, concurrency, and rails **URL:** \ **Category:** Rails\ **Created:** [August 19, 2010, 5:55pm UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560 "2010-08-19T17:55:49Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![zbrod](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/278dde/32.png) [@zbrod](https://www.ruby-forum.com/u/zbrod)\ **Post date:** [August 19, 2010, 5:55pm UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560/1 "2010-08-19T17:55:49Z")
I work on a fairly large website that uses Ruby 1.8.6 and Rails 1.2.3. We cannot upgrade as it will hopelessly break our code. We are working on a new version in Java but for the next year at least we are stuck with the legacy system. We use the latest version of Postgresql for the database using the postgres-pr gem. I am attempting to implement cron tasks within the system using Rufus Scheduler, which is sort of a lighter-weight version of BackgrounDRb. I found very quickly that if I have 2 tasks (threads) running and they both attempt to use ActiveRecord, they deadlock. Supposedly ActiveRecord has a means of enabling concurrency, however the postgres-pr adapter does not support this. I’ve been trying without luck to install one of the alternative postgres adapters that supposedly support concurrency. The ‘pg’ one appears to be the latest and official gem, and it installs fine. However, when I attempt to access a page, I get: “no such file to load – postgres”. I have scoured Google for this error string, but the results have not been helpful. So my first question is: what’s the deal with this? Also: How do you guys use threads in your Rails apps? By the way, I am developing on a Windows box, though our production systems are FreeBSD. Thanks If you want to continue reading, I have more random notes: I did attempt to install some of the deprecated gems, with no success. The old postgres gem and ruby-pg fail when trying to build native extensions, even when I point them to the postgres install dir (I probably don’t have the necessary dev tools on my workstation). Ruby-postgres (the older version of pg) installs find but doesn’t play nicely with the latest version of postgresql, throwing operating system errors. Really all of this should matter though as the pg gem is the one I should be using. Is there a way to get concurrency working with postgres-pr, or does using that adapter mean you just can’t use threads? Seems pretty piss poor, but typical I guess. Even if I do get the adapter working, do I have to worry about deadlock in other parts of Rails besides ActiveRecord? ---
**Author:** ![zbrod](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/278dde/32.png) [@zbrod](https://www.ruby-forum.com/u/zbrod)\ **Post date:** [August 19, 2010, 10:01pm UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560/2 "2010-08-19T22:01:29Z")
After some more epic Googling (literally like 10+ hours of just slogging through crap) I’ve gotten a little further in my search, for anyone who is having similar problems. It seems that the supposedly ‘latest’ Postgres adapter, pg, doesn’t work with Rails at all, or at least version 1.2.3. You need to use ruby-postgres. You will have some issues with some DLL files because Postgres 8.4 uses a newer version of SSL or some sort. It is all explained here: > **[Getting PostgreSQL to install on Windows](https://rubyonrailswin.wordpress.com/2010/03/12/getting-postgresql-to-install-on-windows/)** > > In the effort to migrate my existing Rails app from Slicehost to Heroku, I encountered some MySQL – PostgreSQL compatibility issues, I’ll write a separate post on Heroku gotchas later. … If anyone has any more insight into the concurrency thing, I would still love feedback. Thanks. ---
**Author:** ![zbrod](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/278dde/32.png) [@zbrod](https://www.ruby-forum.com/u/zbrod)\ **Post date:** [August 19, 2010, 10:23pm UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560/3 "2010-08-19T22:23:22Z")
On Thu, Aug 19, 2010 at 3:01 PM, Zach B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > It seems that the supposedly ‘latest’ Postgres adapter, pg, doesn’t work > with Rails at all, or at least version 1.2.3. You need to use > ruby-postgres. I am using pg (0.9.0) with Rails 3.0-rc and it works fine. I did have to uninstall all other Postgres gems for it to work however. – Greg D. [destiney.com](http://destiney.com) | [gregdonald.com](http://gregdonald.com) ---
**Author:** ![zbrod](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/278dde/32.png) [@zbrod](https://www.ruby-forum.com/u/zbrod)\ **Post date:** [August 20, 2010, 9:50am UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560/4 "2010-08-20T09:50:13Z")
Zach B. wrote: > It must be the ancient version of Rails we are using then. The > postgresql\_adapter requires a gem (whatever version, postgres-pr, > ruby-postgres, etc) that calls itself ‘postgres’, and I imagine pg only > responds to ‘pg’. Perhaps Rails 3.0 requires either postgres OR pg. It > might be possible I could modify the adapter but that is probably asking > for trouble. I remember the pain in finding the correct postgresql ruby gem. Indeed the latest gem is called “pg”, however I can’t remember it was compatible at the time of Rails 1.2 but I guess so. Maybe use an older “pg” gem as Rails has been modified a lot since and so was pg. ---
**Author:** ![zbrod](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/278dde/32.png) [@zbrod](https://www.ruby-forum.com/u/zbrod)\ **Post date:** [August 19, 2010, 10:34pm UTC](https://www.ruby-forum.com/t/postgres-concurrency-and-rails/193560/5 "2010-08-19T22:34:50Z")
It must be the ancient version of Rails we are using then. The postgresql\_adapter requires a gem (whatever version, postgres-pr, ruby-postgres, etc) that calls itself ‘postgres’, and I imagine pg only responds to ‘pg’. Perhaps Rails 3.0 requires either postgres OR pg. It might be possible I could modify the adapter but that is probably asking for trouble. Either way though, ruby-postgres seems to work fine so far. It no longer deadlocks. However, calling allow\_concurrency = true on ActiveRecord seems to cause the server to hang. After I commented it out, however, things went fine and there was no deadlock. I do get messages from postgres such as “warning: transaction in progress”, which I’m guessing is the result of my threads hitting the same table at the same time (I did this on purpose to test). I’m guessing that allow\_concurrency is supposed to prevent this by making ActiveRecord queue up these transactions, but like I said it seems to make the server hang. So the question really is, can postgres handle these overlapping transactions? It seems to do a good job queueing them up so far, but I guess we’ll have to see. Again, any insight is appreciated.