Merge pull request #8417 from kennyj/fix_8414

Fix #8414. Performance problem with postgresql adapter primary_key function.
Conflicts:
	activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

activerecord/CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Rails 3.2.10 (unreleased)
 
+*   Fix performance problem with primary_key method in PostgreSQL adapter when having many schemas.
+    Uses pg_constraint table instead of pg_depend table which has many records in general.
+    Fix #8414
+
+    *kennyj*
+
 *   Do not instantiate intermediate Active Record objects when eager loading.
     These records caused `after_find` to run more than expected.
     Fix #3313

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -988,12 +988,11 @@ def pk_and_sequence_for(table) #:nodoc:
       # Returns just a table's primary key
       def primary_key(table)
         row = exec_query(<<-end_sql, 'SCHEMA').rows.first
-          SELECT DISTINCT(attr.attname)
+          SELECT attr.attname
           FROM pg_attribute attr
-          INNER JOIN pg_depend dep ON attr.attrelid = dep.refobjid AND attr.attnum = dep.refobjsubid
           INNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = cons.conkey[1]
           WHERE cons.contype = 'p'
-            AND dep.refobjid = '#{quote_table_name(table)}'::regclass
+            AND cons.conrelid = '#{quote_table_name(table)}'::regclass
         end_sql
 
         row && row.first