memcached: Allow overriding the max-item-size.

This is necessary for organizations with extremely large numbers of
members (20k+).

docs/production/deployment.md

@@ -800,6 +800,12 @@ The version of PostgreSQL that is in use. Do not set by hand; use the
 Override the number of megabytes of memory that memcached should be
 configured to consume; defaults to 1/8th of the total server memory.
 
+#### `max_item_size`
+
+Override the maximum size that an item in memcached can store. This defaults to
+1m; adjusting it should only be necessary if your Zulip server has organizations
+which have more than 20k users.
+
 ### `[loadbalancer]`
 
 #### `ips`

puppet/zulip/manifests/profile/memcached.pp

@@ -18,6 +18,7 @@ class zulip::profile::memcached {
   }
   package { $memcached_packages: ensure => installed }
 
+  $memcached_max_item_size = zulipconf('memcached', 'max_item_size', '1m')
   $memcached_memory = zulipconf('memcached', 'memory', $zulip::common::total_memory_mb / 8)
   file { '/etc/sasl2':
     ensure => directory,

puppet/zulip/templates/memcached.conf.template.erb

@@ -51,3 +51,7 @@ logfile /var/log/memcached.log
 
 # Enable SASL authentication
 -S
+<% if @memcached_max_item_size != '1m' %>
+# Larger max-item-size
+-I <%= @memcached_max_item_size %>
+<% end -%>