libpq: Try next host if one of them times out.

If one host in a multi-host connection string times out, move on to
the next specified host instead of giving up entirely.

Takayuki Tsunakawa, reviewed by Michael Paquier.  I added
a minor adjustment to the documentation.

Discussion: http://postgr.es/m/0A3221C70F24FB45833433255569204D1F6F42F5@G01JPEXMBYT05

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index d20d3140821fdb9e88887f0c35457d382e0b49cb..493cc12d61e438bb81f9fbab39e11958f135331f 100644 (file)
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1041,9 +1041,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
        string). Zero or not specified means wait indefinitely.  It is not
        recommended to use a timeout of less than 2 seconds.
        This timeout applies separately to each connection attempt.
-       For example, if you specify two hosts and both of them are unreachable,
-       and <literal>connect_timeout</> is 5, the total time spent waiting for a
-       connection might be up to 10 seconds.
+       For example, if you specify two hosts and <literal>connect_timeout</>
+       is 5, each host will time out if no connection is made within 5
+       seconds, so the total time spent waiting for a connection might be
+       up to 10 seconds.
       </para>
       </listitem>
      </varlistentry>

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 8e3ef4b9f75086f7c1ce72a0e86ff65f481c618f..f2c9bf7a883235734281e462352e6f83ccccf938 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -1720,6 +1720,7 @@ connectDBComplete(PGconn *conn)
 {
    PostgresPollingStatusType flag = PGRES_POLLING_WRITING;
    time_t      finish_time = ((time_t) -1);
+   int         timeout = 0;
 
    if (conn == NULL || conn->status == CONNECTION_BAD)
        return 0;
@@ -1729,8 +1730,7 @@ connectDBComplete(PGconn *conn)
     */
    if (conn->connect_timeout != NULL)
    {
-       int         timeout = atoi(conn->connect_timeout);
-
+       timeout = atoi(conn->connect_timeout);
        if (timeout > 0)
        {
            /*
@@ -1745,6 +1745,8 @@ connectDBComplete(PGconn *conn)
 
    for (;;)
    {
+       int         ret = 0;
+
        /*
         * Wait, if necessary.  Note that the initial state (just after
         * PQconnectStart) is to wait for the socket to select for writing.
@@ -1761,7 +1763,8 @@ connectDBComplete(PGconn *conn)
                return 1;       /* success! */
 
            case PGRES_POLLING_READING:
-               if (pqWaitTimed(1, 0, conn, finish_time))
+               ret = pqWaitTimed(1, 0, conn, finish_time);
+               if (ret == -1)
                {
                    conn->status = CONNECTION_BAD;
                    return 0;
@@ -1769,7 +1772,8 @@ connectDBComplete(PGconn *conn)
                break;
 
            case PGRES_POLLING_WRITING:
-               if (pqWaitTimed(0, 1, conn, finish_time))
+               ret = pqWaitTimed(0, 1, conn, finish_time);
+               if (ret == -1)
                {
                    conn->status = CONNECTION_BAD;
                    return 0;
@@ -1782,6 +1786,23 @@ connectDBComplete(PGconn *conn)
                return 0;
        }
 
+       if (ret == 1)   /* connect_timeout elapsed */
+       {
+           /* If there are no more hosts, return (the error message is already set) */
+           if (++conn->whichhost >= conn->nconnhost)
+           {
+               conn->whichhost = 0;
+               conn->status = CONNECTION_BAD;
+               return 0;
+           }
+           /* Attempt connection to the next host, starting the connect_timeout timer */
+           pqDropConnection(conn, true);
+           conn->addr_cur = conn->connhost[conn->whichhost].addrlist;
+           conn->status = CONNECTION_NEEDED;
+           if (conn->connect_timeout != NULL)
+               finish_time = time(NULL) + timeout;
+       }
+
        /*
         * Now try to advance the state machine.
         */

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 756c6d77790e042ded6c2907da355778438bba82..1d6ea93a0a9d3debe5d18fed464eefec57d49c67 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -991,11 +991,9 @@ pqWait(int forRead, int forWrite, PGconn *conn)
 /*
  * pqWaitTimed: wait, but not past finish_time.
  *
- * If finish_time is exceeded then we return failure (EOF).  This is like
- * the response for a kernel exception because we don't want the caller
- * to try to read/write in that case.
- *
  * finish_time = ((time_t) -1) disables the wait limit.
+ *
+ * Returns -1 on failure, 0 if the socket is readable/writable, 1 if it timed out.
  */
 int
 pqWaitTimed(int forRead, int forWrite, PGconn *conn, time_t finish_time)
@@ -1005,13 +1003,13 @@ pqWaitTimed(int forRead, int forWrite, PGconn *conn, time_t finish_time)
    result = pqSocketCheck(conn, forRead, forWrite, finish_time);
 
    if (result < 0)
-       return EOF;             /* errorMessage is already set */
+       return -1;              /* errorMessage is already set */
 
    if (result == 0)
    {
        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("timeout expired\n"));
-       return EOF;
+       return 1;
    }
 
    return 0;