Index: trac/db.py
===================================================================
--- trac/db.py	(revision 3347)
+++ trac/db.py	(working copy)
@@ -351,11 +351,12 @@
 
 psycopg = None
 PgSQL = None
+PGSchemaError = None
 
 class PostgreSQLConnection(ConnectionWrapper):
     """Connection wrapper for PostgreSQL."""
 
-    __slots__ = ['cnx']
+    __slots__ = ['cnx', 'schema']
 
     poolable = True
 
@@ -366,14 +367,18 @@
         # We support both psycopg and PgSQL but prefer psycopg
         global psycopg
         global PgSQL
+        global PGSchemaError
         if not psycopg and not PgSQL:
             try:
                 try:
                     import psycopg2 as psycopg
+                    from psycopg2 import ProgrammingError as PGSchemaError
                 except ImportError:
                     import psycopg
+                    from psycopg import ProgrammingError as PGSchemaError
             except ImportError:
                 from pyPgSQL import PgSQL
+                from pyPgSQL.libpq import OperationalError as PGSchemaError
         if psycopg:
             dsn = []
             if path:
@@ -389,6 +394,14 @@
             cnx = psycopg.connect(' '.join(dsn))
         else:
             cnx = PgSQL.connect('', user, password, host, path, port)
+        try: 
+            self.schema = None 
+            if 'schema' in params: 
+                self.schema = params['schema'] 
+                cnx.cursor().execute('SET search_path TO %s, public',  
+                                    (self.schema,)) 
+        except PGSchemaError: 
+            cnx.rollback() 
         ConnectionWrapper.__init__(self, cnx)
 
     def cast(self, column, type):
@@ -407,6 +420,9 @@
     def init_db(cls, **args):
         self = cls(**args)
         cursor = self.cursor()
+        if self.schema: 
+            cursor.execute('CREATE SCHEMA %s' % self.schema) 
+            cursor.execute('SET search_path TO %s, public', (self.schema,)) 
         from trac.db_default import schema
         for table in schema:
             for stmt in cls.to_sql(table):
@@ -434,7 +450,16 @@
                    '_'.join(index.columns), table.name, ','.join(index.columns))
     to_sql = classmethod(to_sql)
 
+    def rollback(self): 
+        self.cnx.rollback() 
+        if self.schema: 
+            try: 
+                self.cnx.cursor().execute("SET search_path TO %s, public",  
+                                            (self.schema,)) 
+            except PGSchemaError: 
+                self.cnx.rollback() 
 
+
 _cnx_map = {'postgres': PostgreSQLConnection, 'sqlite': SQLiteConnection}
 
 def init_db(env_path, db_str):