Adjust libpq to avoid deadlock when both client and server want to send

data, and both have filled the transmission buffers.  One scenario where
this can happen was illustrated here:
http://archives.postgresql.org/pgsql-hackers/2003-04/msg00979.php

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 810a753ed3c7565e1dd7194daf7b60a5922708be..1967d7429b44d96ecf2abf05af21ea7c75620f75 100644 (file)
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.151 2003/10/04 21:05:21 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.152 2003/10/19 21:36:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1336,6 +1336,17 @@ PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
                                                  libpq_gettext("no COPY in progress\n"));
                return -1;
        }
+
+       /*
+        * Check for NOTICE messages coming back from the server.  Since the
+        * server might generate multiple notices during the COPY, we have to
+        * consume those in a reasonably prompt fashion to prevent the comm
+        * buffers from filling up and possibly blocking the server.
+        */
+       if (!PQconsumeInput(conn))
+               return -1;                              /* I/O failure */
+       parseInput(conn);
+
        if (nbytes > 0)
        {
                /*

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index d71473d514ae591145c3eacebff64981cb3382ea..4349a4e05aa5bdf35bf87910a685fcb8f6fcff57 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.102 2003/08/08 21:42:55 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.103 2003/10/19 21:36:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -828,7 +828,24 @@ pqSendSome(PGconn *conn, int len)
                                break;
                        }
 
-                       if (pqWait(FALSE, TRUE, conn))
+                       /*
+                        * There are scenarios in which we can't send data because the
+                        * communications channel is full, but we cannot expect the server
+                        * to clear the channel eventually because it's blocked trying to
+                        * send data to us.  (This can happen when we are sending a large
+                        * amount of COPY data, and the server has generated lots of
+                        * NOTICE responses.)  To avoid a deadlock situation, we must be
+                        * prepared to accept and buffer incoming data before we try
+                        * again.  Furthermore, it is possible that such incoming data
+                        * might not arrive until after we've gone to sleep.  Therefore,
+                        * we wait for either read ready or write ready.
+                        */
+                       if (pqReadData(conn) < 0)
+                       {
+                               result = -1;    /* error message already set up */
+                               break;
+                       }
+                       if (pqWait(TRUE, TRUE, conn))
                        {
                                result = -1;
                                break;