Ruby on Rails

On Aug 1, 2011, at 2:39 PM, Michael Kintzer wrote:

> I have recently been investigating using PosgreSQL (server version
> 8.3.12), with the 'pg' gem '0.11.0', with our Rails 3.0.7 app. I've
> noticed in the development.log that column information queries are
> made after each request. After inspecting the code for the
> postgresql_adapter and the mysql_adapter I noticed that the
> mysql_adapter executes a similar query but with the :skip_logging
> flag, while the postgresql_adapter goes ahead noisily and logs the
> query:
>
> In PostgreSQL, the queries are similar to:
>
> SQL (4.4ms) SELECT a.attname, format_type(a.atttypid, a.atttypmod),
> d.adsrc, a.attnotnull
> FROM pg_attribute a LEFT JOIN pg_attrdef d
> ON a.attrelid = d.adrelid AND a.attnum = d.adnum
> WHERE a.attrelid = '"users"'::regclass
> AND a.attnum > 0 AND NOT a.attisdropped
> ORDER BY a.attnum
>
> These queries take real time in development mode, so being worried
> about performance I added some extra logging in both adapters to see
> if these queries are also being made in production mode, and to my
> surprise they were made repeatedly for tables with both adapters. I
> was under the impression that ActiveRecord caches table column
> information (at least in production mode) for a given table after the
> first query, and does not need to re-query this information unless the
> client calls the ActiveRecord::Base.reset_column_information method.
>
> What's going on here? Am I missing a configuration option that
> enables table column information caching? Or am I just
> misunderstanding the basic concept?

I think you'll find that (the local equivalent of) these queries
happen all the time in all database servers when you're in development
mode. Production mode enables all the caches, and you won't see them
any more, or certainly not as often!

Walter

>
> Thanks,
>
> Michael
>
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