Randomize matrix-synapse-auto-compressor.timer start with a RandomizedDelaySec (defaults to 6h)

Author: spantaleev

docs/configuring-playbook-synapse-auto-compressor.md

@@ -24,12 +24,15 @@ matrix_synapse_auto_compressor_enabled: true
 
 ### Edit the schedule (optional)
 
-By default the task will run 0 a.m. every day based on the `matrix_synapse_auto_compressor_schedule` variable. It is defined in the format of systemd timer calendar.
+By default the task will around 0 a.m. every day based on the `matrix_synapse_auto_compressor_schedule` variable with a randomized delay of 6 hours (controlled by the `matrix_synapse_auto_compressor_schedule_randomized_delay_sec` variable). It is defined in the format of systemd timer calendar.
 
 To edit the schedule, add the following configuration to your `vars.yml` file (adapt to your needs):
 
 ```yaml
 matrix_synapse_auto_compressor_schedule: "*-*-* 00:00:00"
+
+# Consider adjusting the randomized delay or setting it to 0 to disable randomized delays.
+# matrix_synapse_auto_compressor_schedule_randomized_delay_sec: 6h
 ```
 
 ### Extending the configuration

roles/custom/matrix-synapse-auto-compressor/defaults/main.yml

@@ -64,9 +64,14 @@ matrix_synapse_auto_compressor_database_name: 'synapse'
 # connection string to synapse database (postgres only)
 matrix_synapse_auto_compressor_synapse_database: 'postgres://{{ matrix_synapse_auto_compressor_database_username | urlencode() }}:{{ matrix_synapse_auto_compressor_database_password | urlencode() }}@{{ matrix_synapse_auto_compressor_database_hostname }}:{{ matrix_synapse_auto_compressor_database_port }}/{{ matrix_synapse_auto_compressor_database_name }}'
 
-# systemd calendar configuration for the compressor job
+# Controls the `OnCalendar` configuration for the compressor job.
+# Also see: `matrix_synapse_auto_compressor_schedule_randomized_delay_sec`
 matrix_synapse_auto_compressor_schedule: "*-*-* 00:00:00"
 
+# The `RandomizedDelaySec` delay (in seconds or as a systemd time string) to randomize the `OnCalendar` start time (`matrix_synapse_auto_compressor_schedule`) of the compressor job.
+# This can be set to 0 to disable randomized delays.
+matrix_synapse_auto_compressor_schedule_randomized_delay_sec: 6h
+
 # The number of state groups to work on at once.
 # All of the entries from state_groups_state are requested from the database for state groups that are worked on.
 # Therefore small chunk sizes may be needed on machines with low memory.

roles/custom/matrix-synapse-auto-compressor/templates/matrix-synapse-auto-compressor.timer.j2

@@ -11,6 +11,7 @@ Description=Synapse State Auto Compressor Timer
 [Timer]
 Unit=matrix-synapse-auto-compressor.service
 OnCalendar={{ matrix_synapse_auto_compressor_schedule }}
+RandomizedDelaySec={{ matrix_synapse_auto_compressor_schedule_randomized_delay_sec }}
 
 [Install]
 WantedBy=timers.target