early_exit_20120228.diff

diff --git b/doc/src/sgml/libpq.sgml a/doc/src/sgml/libpq.sgml
index 1245e85..5ef89e7 100644
--- b/doc/src/sgml/libpq.sgml
+++ a/doc/src/sgml/libpq.sgml
@@ -7353,7 +7353,16 @@ typedef struct
        releases the PGresult under construction. If you set any
        message with <function>PQresultSetErrMsg</function>, it is set
        as the PGconn's error message and the PGresult will be
-       preserved.
+       preserved.  When non-blocking API is in use, it can also return
+       2 for early exit from <function>PQisBusy</function> function.
+       The supplied <parameter>res</parameter>
+       and <parameter>columns</parameter> values will stay valid so
+       row can be processed outside of callback.  Caller is
+       responsible for tracking whether
+       the <parameter>PQisBusy</parameter> returned early from
+       callback or for other reasons.  Usually this should happen via
+       setting cached values to NULL before
+       calling <function>PQisBusy</function>.
      </para>
 
      <para>
diff --git b/src/interfaces/libpq/fe-protocol2.c a/src/interfaces/libpq/fe-protocol2.c
index 6555f85..36773cb 100644
--- b/src/interfaces/libpq/fe-protocol2.c
+++ a/src/interfaces/libpq/fe-protocol2.c
@@ -828,6 +828,9 @@ getAnotherTuple(PGconn *conn, bool binary)
 	rp= conn->rowProcessor(result, rowbuf, conn->rowProcessorParam);
 	if (rp == 1)
 		return 0;
+	else if (rp == 2 && pqIsnonblocking(conn))
+		/* processor requested early exit */
+		return EOF;
 	else if (rp == 0)
 	{
 		errmsg = result->errMsg;
diff --git b/src/interfaces/libpq/fe-protocol3.c a/src/interfaces/libpq/fe-protocol3.c
index 3725de2..2693ce0 100644
--- b/src/interfaces/libpq/fe-protocol3.c
+++ a/src/interfaces/libpq/fe-protocol3.c
@@ -698,6 +698,11 @@ getAnotherTuple(PGconn *conn, int msgLength)
 		/* everything is good */
 		return 0;
 	}
+	if (rp == 2 && pqIsnonblocking(conn))
+	{
+		/* processor requested early exit */
+		return EOF;
+	}
 
 	/* there was some problem */
 	if (rp == 0)