MFC r316342, r316358

r316342:
Consolidate random sleeps in periodic scripts

Multiple periodic scripts sleep for a random amount of time in order to
mitigate the thundering herd problem. This is bad, because the sum of
multiple uniformly distributed random variables approaches a normal
distribution, so the problem isn't mitigated as effectively as it would be
with a single sleep.

This change creates a single configurable anticongestion sleep. periodic
will only sleep if at least one script requires it, and it will never sleep
more than once per invocation. It also won't sleep if periodic was run
interactively, fixing an unrelated longstanding bug.

PR:		217055
PR:		210188
Reviewed by:	cy
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D10211

r316358:
Fix man page typo from r316342

Reported by:	rgrimes
MFC after:	20 days
X-MFC-With:	316342

2 files changed, 17 insertions, 12 deletions

diff --git a/etc/defaults/periodic.conf b/etc/defaults/periodic.conf
index 16de38e..b3be114 100644
--- a/etc/defaults/periodic.conf
+++ b/etc/defaults/periodic.conf
@@ -22,6 +22,8 @@ periodic_conf_files="/etc/periodic.conf /etc/periodic.conf.local"
 # periodic script dirs
 local_periodic="/usr/local/etc/periodic"
 
+# Max time to sleep to avoid causing congestion on download servers
+anticongestion_sleeptime=3600
 
 # Daily options
 
@@ -136,8 +138,6 @@ daily_status_mail_rejects_shorten="NO"			# Shorten output
 
 # 480.leapfile-ntpd
 daily_ntpd_leapfile_enable="YES"			# Fetch NTP leapfile
-daily_ntpd_avoid_congestion="YES"			# Avoid congesting
-							# leapfile sources
 
 # 480.status-ntpd
 daily_status_ntpd_enable="NO"				# Check NTP status
@@ -307,6 +307,18 @@ security_status_tcpwrap_period="daily"
 if [ -z "${source_periodic_confs_defined}" ]; then
         source_periodic_confs_defined=yes
 
+	# Sleep for a random amount of time in order to mitigate the thundering
+	# herd problem of multiple hosts running periodic simultaneously.
+	# Will not sleep when used interactively.
+	# Will sleep at most once per invocation of periodic
+	anticongestion() {
+		[ -n "$PERIODIC_IS_INTERACTIVE" ] && return
+		if [ -f "$PERIODIC_ANTICONGESTION_FILE" ]; then
+			rm -f $PERIODIC_ANTICONGESTION_FILE
+			sleep `jot -r 1 0 ${anticongestion_sleeptime}`
+		fi
+	}
+
 	# Compatibility with old daily variable names.
 	# They can be removed in stable/11.
 	security_daily_compat_var() {
diff --git a/etc/periodic/daily/480.leapfile-ntpd b/etc/periodic/daily/480.leapfile-ntpd
index 8a38364..6b2a1f3 100755
--- a/etc/periodic/daily/480.leapfile-ntpd
+++ b/etc/periodic/daily/480.leapfile-ntpd
@@ -13,16 +13,9 @@ fi
 
 case "$daily_ntpd_leapfile_enable" in
     [Yy][Ee][Ss])
-	case "$daily_ntpd_avoid_congestion" in
-    	[Yy][Ee][Ss])
-	    # Avoid dogpiling
-	    (sleep $(jot -r 1 0 3600); service ntpd onefetch) &
-	    ;;
-	*)
-	    service ntpd onefetch
-	    ;;
-	esac
-	;;
+        anticongestion
+        service ntpd onefetch
+        ;;
 esac
 
 exit $rc