Second try at fixing tcp_keepalives_idle option on Solaris.

Buildfarm evidence shows that TCP_KEEPALIVE_THRESHOLD doesn't exist
after all on Solaris < 11.  This means we need to take positive action to
prevent the TCP_KEEPALIVE code path from being taken on that platform.
I've chosen to limit it with "&& defined(__darwin__)", since it's unclear
that anyone else would follow Apple's precedent of spelling the symbol
that way.

Also, follow a suggestion from Michael Paquier of eliminating code
duplication by defining a couple of intermediate symbols for the
socket option.

In passing, make some effort to reduce the number of translatable messages
by replacing "setsockopt(foo) failed" with "setsockopt(%s) failed", etc,
throughout the affected files.  And update relevant documentation so
that it doesn't claim to provide an exhaustive list of the possible
socket option names.

Like the previous commit (f0256c774), back-patch to all supported branches.

Discussion: https://postgr.es/m/20170627163757.25161.528@wrigleys.postgresql.org

2 files changed, 19 insertions, 17 deletions

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 0611104dfce..e0ee139b367 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -677,8 +677,8 @@ include 'filename'
        <para>
         Specifies the number of seconds before sending a keepalive packet on
         an otherwise idle connection.  A value of 0 uses the system default.
-        This parameter is supported only on systems that support the
-        <symbol>TCP_KEEPIDLE</> or <symbol>TCP_KEEPALIVE</> symbols, and on
+        This parameter is supported only on systems that support
+        <symbol>TCP_KEEPIDLE</> or an equivalent socket option, and on
         Windows; on other systems, it must be zero.
         In sessions connected via a Unix-domain socket, this parameter is
         ignored and always reads as zero.
@@ -701,9 +701,9 @@ include 'filename'
        <para>
         Specifies the number of seconds between sending keepalives on an
         otherwise idle connection.  A value of 0 uses the system default.
-        This parameter is supported only on systems that support the
-        <symbol>TCP_KEEPINTVL</> symbol, and on Windows; on other systems, it
-        must be zero.
+        This parameter is supported only on systems that support
+        <symbol>TCP_KEEPINTVL</> or an equivalent socket option, and on
+        Windows; on other systems, it must be zero.
         In sessions connected via a Unix-domain socket, this parameter is
         ignored and always reads as zero.
        </para>
@@ -724,9 +724,10 @@ include 'filename'
       <listitem>
        <para>
         Specifies the number of keepalive packets to send on an otherwise idle
-        connection.  A value of 0 uses the system default.  This parameter is
-        supported only on systems that support the <symbol>TCP_KEEPCNT</>
-        symbol; on other systems, it must be zero.
+        connection.  A value of 0 uses the system default.
+        This parameter is supported only on systems that support
+        <symbol>TCP_KEEPCNT</> or an equivalent socket option;
+        on other systems, it must be zero.
         In sessions connected via a Unix-domain socket, this parameter is
         ignored and always reads as zero.
        </para>
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 14d54da43c0..bc54c057c7c 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1069,10 +1069,10 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         Controls the number of seconds of inactivity after which TCP should
         send a keepalive message to the server.  A value of zero uses the
         system default. This parameter is ignored for connections made via a
-        Unix-domain socket, or if keepalives are disabled. It is only supported
-        on systems where the <symbol>TCP_KEEPIDLE</> or <symbol>TCP_KEEPALIVE</>
-        socket option is available, and on Windows; on other systems, it has no
-        effect.
+        Unix-domain socket, or if keepalives are disabled.
+        It is only supported on systems where <symbol>TCP_KEEPIDLE</> or
+        an equivalent socket option is available, and on Windows; on other
+        systems, it has no effect.
        </para>
       </listitem>
      </varlistentry>
@@ -1085,9 +1085,9 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         that is not acknowledged by the server should be retransmitted.  A
         value of zero uses the system default. This parameter is ignored for
         connections made via a Unix-domain socket, or if keepalives are disabled.
-        It is only supported on systems where the <symbol>TCP_KEEPINTVL</>
-        socket option is available, and on Windows; on other systems, it has no
-        effect.
+        It is only supported on systems where <symbol>TCP_KEEPINTVL</> or
+        an equivalent socket option is available, and on Windows; on other
+        systems, it has no effect.
        </para>
       </listitem>
      </varlistentry>
@@ -1100,8 +1100,9 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         client's connection to the server is considered dead.  A value of
         zero uses the system default. This parameter is ignored for
         connections made via a Unix-domain socket, or if keepalives are disabled.
-        It is only supported on systems where the <symbol>TCP_KEEPCNT</>
-        socket option is available; on other systems, it has no effect.
+        It is only supported on systems where <symbol>TCP_KEEPCNT</> or
+        an equivalent socket option is available; on other systems, it has no
+        effect.
        </para>
       </listitem>
      </varlistentry>