From 9dfdbef345390124eaf993f6289e8ae796aa6918 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 19 Oct 2003 21:36:41 +0000
Subject: [PATCH] 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
---
src/interfaces/libpq/fe-exec.c | 13 ++++++++++++-
src/interfaces/libpq/fe-misc.c | 21 +++++++++++++++++++--
2 files changed, 31 insertions(+), 3 deletions(-)
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 810a753ed3c..1967d7429b4 100644
--- 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 d71473d514a..4349a4e05aa 100644
--- 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;
--
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