Fix #8414. Performance problem with postgresql adapter primary_key function.

1 files changed, 2 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 9f7086cd07..18bf14d1fb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -305,12 +305,11 @@ module ActiveRecord
         # 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