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?
Thanks,
Michael