Use ppoll(2), if available, to wait for input in pgbench.

Previously, pgbench always used select(2) for this purpose, but that's
problematic for very high client counts, because select() can't deal
with file descriptor numbers larger than FD_SETSIZE.  It's pretty common
for that to be only 1024 or so, whereas modern OSes can allow many more
open files than that.  Using poll(2) would surmount that problem, but it
creates another one: poll()'s timeout resolution is only 1ms, which is
poor enough to cause problems with --rate specifications approaching or
exceeding 1K TPS.

On platforms that have ppoll(2), which includes Linux and recent
FreeBSD, we can use that to avoid the FD_SETSIZE problem without any
loss of timeout resolution.  Hence, add configure logic to test for
ppoll(), and use it if available.

This patch introduces an abstraction layer into pgbench that could
be extended to support other kernel event-wait APIs such as kevents.
But actually adding such support is a matter for some future patch.

Doug Rady, reviewed by Robert Haas and Fabien Coelho, and whacked around
a good bit more by me

Discussion: https://postgr.es/m/23D017C9-81B7-484D-8490-FD94DEC4DF59@amazon.com

configure

@@ -15093,7 +15093,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l
+for ac_func in cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

configure.in

@@ -1562,7 +1562,7 @@ PGAC_FUNC_WCSTOMBS_L
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l])
+AC_CHECK_FUNCS([cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in

src/include/pg_config.h.in

@@ -443,6 +443,9 @@
 /* Define to 1 if the assembler supports PPC's LWARX mutex hint bit. */
 #undef HAVE_PPC_LWARX_MUTEX_HINT
 
+/* Define to 1 if you have the `ppoll' function. */
+#undef HAVE_PPOLL
+
 /* Define to 1 if you have the `pstat' function. */
 #undef HAVE_PSTAT
 

src/include/pg_config.h.win32

@@ -327,6 +327,9 @@
 /* Define to 1 if you have the `posix_fallocate' function. */
 /* #undef HAVE_POSIX_FALLOCATE */
 
+/* Define to 1 if you have the `ppoll' function. */
+/* #undef HAVE_PPOLL */
+
 /* Define to 1 if you have the `pstat' function. */
 /* #undef HAVE_PSTAT */
 

src/template/linux

@@ -6,6 +6,7 @@ if test x"$PREFERRED_SEMAPHORES" = x"" ; then
 fi
 
 # Force _GNU_SOURCE on; plperl is broken with Perl 5.8.0 otherwise
+# This is also required for ppoll(2), and perhaps other things
 CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
 
 # If --enable-profiling is specified, we need -DLINUX_PROFILE