Don't inconditionately run a query at connection to set datestyle to ISO.

Run it only if PQparameterStatus() reports the datestyle is set to
something different.

ChangeLog

@@ -6,9 +6,12 @@
 	* psycopg/connection_int.c: dropped support for protocol 2 at compile
 	time and protocol 2-specific code.
 
-	* psycopg/connection_int.c: don't run a query at connection to detect
+	* psycopg/connection_int.c: don't run a query at every connection to detect
 	client encoding: use PQparameterStatus() instead.
 
+	* psycopg/connection_int.c: don't run a query at every connection to set
+	the datestyle to ISO if PQparameterStatus() reports it already is.
+
 2010-11-11  Daniele Varrazzo  <daniele.varrazzo@gmail.com>
 
 	* lib/extras.py: build the namedtuple only once per execution, not once

NEWS-2.3

@@ -15,7 +15,9 @@ psycopg 2.3 aims to expose some new features introduced in PostgreSQL 9.0.
 
   - Dropped support for protocol 2: Psycopg 2.3 can only connect to PostgreSQL
     servers with version at least 7.4.
-  - don't issue a query at every connection to detect the client encoding.
+  - don't issue a query at every connection to detect the client encoding
+    and to set the datestyle to ISO if it is already compatible with what
+    expected.
   - `mogrify()` now supports unicode queries.
   - subclasses of a type that can be adapted are adapted as the superclass.
   - `errorcodes` knows a couple of new codes introduced in PostgreSQL 9.0.

psycopg/connection_int.c

@@ -292,6 +292,22 @@ conn_get_server_version(PGconn *pgconn)
 }
 
 
+/* Return 1 if the server datestyle allows us to work without problems,
+   0 if it needs to be set to something better, e.g. ISO. */
+static int
+conn_is_datestyle_ok(PGconn *pgconn)
+{
+    const char *ds;
+
+    ds = PQparameterStatus(pgconn, "DateStyle");
+    Dprintf("conn_connect: DateStyle %s", ds);
+
+    /* Return true if ds starts with "ISO"
+     * e.g. "ISO, DMY" is fine, "German" not. */
+    return (ds[0] == 'I' && ds[1] == 'S' && ds[2] == 'O');
+}
+
+
 /* conn_setup - setup and read basic information about the connection */
 
 int
@@ -323,8 +339,10 @@ conn_setup(connectionObject *self, PGconn *pgconn)
         return -1;
     }
 
+    if (!conn_is_datestyle_ok(self->pgconn)) {
         if (!green) {
             Py_UNBLOCK_THREADS;
+            Dprintf("conn_connect: exec query \"%s\";", psyco_datestyle);
             pgres = PQexec(pgconn, psyco_datestyle);
             Py_BLOCK_THREADS;
         } else {
@@ -340,6 +358,7 @@ conn_setup(connectionObject *self, PGconn *pgconn)
             return -1;
         }
         CLEARPGRES(pgres);
+    }
 
     if (!green) {
         Py_UNBLOCK_THREADS;
@@ -642,6 +661,9 @@ _conn_poll_setup_async(connectionObject *self)
          */
         self->isolation_level = 0;
 
+        /* If the datestyle is ISO or anything else good,
+         * we can skip the CONN_STATUS_DATESTYLE step. */
+        if (!conn_is_datestyle_ok(self->pgconn)) {
             Dprintf("conn_poll: status -> CONN_STATUS_DATESTYLE");
             self->status = CONN_STATUS_DATESTYLE;
             if (0 == pq_send_query(self, psyco_datestyle)) {
@@ -651,6 +673,12 @@ _conn_poll_setup_async(connectionObject *self)
             Dprintf("conn_poll: async_status -> ASYNC_WRITE");
             self->async_status = ASYNC_WRITE;
             res = PSYCO_POLL_WRITE;
+        }
+        else {
+            Dprintf("conn_poll: status -> CONN_STATUS_READY");
+            self->status = CONN_STATUS_READY;
+            res = PSYCO_POLL_OK;
+        }
         break;
 
     case CONN_STATUS_DATESTYLE: