svn commit: r316342 - in head: etc/defaults etc/periodic/daily share/man/man5 usr.sbin/periodic

[Alan Somers]

Author: asomers
Date: Sat Apr  1 04:42:35 2017
New Revision: 316342
URL: https://svnweb.freebsd.org/changeset/base/316342

Log:
  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

Modified:
  head/etc/defaults/periodic.conf
  head/etc/periodic/daily/480.leapfile-ntpd
  head/share/man/man5/periodic.conf.5
  head/usr.sbin/periodic/periodic.sh

Modified: head/etc/defaults/periodic.conf
==============================================================================
--- head/etc/defaults/periodic.conf	Sat Apr  1 01:00:36 2017	(r316341)
+++ head/etc/defaults/periodic.conf	Sat Apr  1 04:42:35 2017	(r316342)
@@ -22,6 +22,8 @@ periodic_conf_files="/etc/periodic.conf 
 # 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"		
 
 # 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() {

Modified: head/etc/periodic/daily/480.leapfile-ntpd
==============================================================================
--- head/etc/periodic/daily/480.leapfile-ntpd	Sat Apr  1 01:00:36 2017	(r316341)
+++ head/etc/periodic/daily/480.leapfile-ntpd	Sat Apr  1 04:42:35 2017	(r316342)
@@ -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

Modified: head/share/man/man5/periodic.conf.5
==============================================================================
--- head/share/man/man5/periodic.conf.5	Sat Apr  1 01:00:36 2017	(r316341)
+++ head/share/man/man5/periodic.conf.5	Sat Apr  1 04:42:35 2017	(r316342)
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 26, 2015
+.Dd March 31, 2015
 .Dt PERIODIC.CONF 5
 .Os
 .Sh NAME
@@ -133,6 +133,10 @@ respectively.
 Refer to the
 .Xr periodic 8
 manual page for how script return codes are interpreted.
+.It Va anticongestion_sleeptime
+.Pq Vt int
+The maximum number of seconds to randomly sleep in order to smooth bursty loads
+on a shared resource, such as a download mirror.
 .El
 .Pp
 The following variables are used by the standard scripts that reside in

Modified: head/usr.sbin/periodic/periodic.sh
==============================================================================
--- head/usr.sbin/periodic/periodic.sh	Sat Apr  1 01:00:36 2017	(r316341)
+++ head/usr.sbin/periodic/periodic.sh	Sat Apr  1 04:42:35 2017	(r316342)
@@ -76,6 +76,12 @@ fi
 shift
 arg=$1
 
+if [ -z "$PERIODIC_ANTICONGESTION_FILE" ] ; then
+	export PERIODIC_ANTICONGESTION_FILE=`mktemp ${TMPDIR:-/tmp}/periodic.anticongestion.XXXXXXXXXX`
+fi
+if tty > /dev/null 2>&1; then
+	export PERIODIC_IS_INTERACTIVE=1
+fi
 tmp_output=`mktemp ${TMPDIR:-/tmp}/periodic.XXXXXXXXXX`
 context="$PERIODIC"
 export PERIODIC="$arg${PERIODIC:+ }${PERIODIC}"
@@ -141,3 +147,4 @@ esac
 } | output_pipe $arg "$context"
 
 rm -f $tmp_output
+rm -f $PERIODIC_ANTICONGESTION_FILE