Changing maxfiles for mongodb on Mac OS

I installed mongodb-community via Homebrew on my Mac OS 10.15.5 and found that mongod sometimes died with Too many open files error. This looked strange because the limit seemed to be set to 64,000 in ~/Library/LaunchAgents/homebrew.mxcl.mongodb-community@4.0.plist.

<?xml version="1.0" encoding="UTF-8"?>

<plist version="1.0">
<dict>
  <key>Label</key>
  <string>homebrew.mxcl.mongodb-community@4.0</string>
  <key>ProgramArguments</key>
  <array>
    <string>/usr/local/opt/mongodb-community@4.0/bin/mongod</string>
    <string>--config</string>
    <string>/usr/local/etc/mongod.conf</string>
  </array>
  <key>RunAtLoad</key>
  <true></true>
  <key>KeepAlive</key>
  <false></false>
  <key>WorkingDirectory</key>
  <string>/usr/local</string>
  <key>StandardErrorPath</key>
  <string>/usr/local/var/log/mongodb/output.log</string>
  <key>StandardOutPath</key>
  <string>/usr/local/var/log/mongodb/output.log</string>
  <key>HardResourceLimits</key>
  <dict>
    <key>NumberOfFiles</key>
    <integer>64000</integer>
  </dict>
  <key>SoftResourceLimits</key>
  <dict>
    <key>NumberOfFiles</key>
    <integer>64000</integer>
  </dict>
</dict>
</plist>

But it turned out that these limits weren’t applied.

To make it work, you’d create /Library/LaunchDaemons/limit.maxfiles.plist including maxfiles configuration and load it by launchctl load /Library/LaunchDaemons/limit.maxfiles.plist

<?xml version="1.0" encoding="UTF-8"?>

<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>limit.maxfiles</string>
    <key>ProgramArguments</key>
    <array>
      <string>launchctl</string>
      <string>limit</string>
      <string>maxfiles</string>
      <string>64000</string>
      <string>64000</string>
    </array>
    <key>RunAtLoad</key>
    <true></true>
    <key>ServiceIPC</key>
    <false></false>
  </dict>
</plist>

launchctl limit shows the current limits.

	cpu         unlimited      unlimited
	filesize    unlimited      unlimited
	data        unlimited      unlimited
	stack       8388608        67104768
	core        0              unlimited
	rss         unlimited      unlimited
	memlock     unlimited      unlimited
	maxproc     2784           4176
	maxfiles    64000          64000

Then, restart the service by brew services restart mongodb-community@4.0.