Print warning if synctl_cache_factor is set in config

changelog.d/11865.removal

@@ -0,0 +1 @@
+Deprecate using `synctl` with the config option `synctl_cache_factor` and print a warning if a user still uses this option.

synctl

@@ -18,6 +18,7 @@ import argparse
 import collections
 import errno
 import glob
+import logging
 import os
 import os.path
 import signal
@@ -37,6 +38,15 @@ YELLOW = "\x1b[1;33m"
 RED = "\x1b[1;31m"
 NORMAL = "\x1b[m"
 
+SYNCTL_CACHE_FACTOR_WARNING = """\
+Setting 'synctl_cache_factor' in the config is deprecated. Instead, please do
+one of the following:
+ - Either set the environment variable 'SYNAPSE_CACHE_FACTOR'
+ - or set 'caches.global_factor' in the configs.
+--------------------------------------------------------------------------------"""
+
+logger = logging.getLogger(__name__)
+
 
 def pid_running(pid):
     try:
@@ -228,6 +238,7 @@ def main():
     start_stop_synapse = True
 
     if cache_factor:
+        logger.warning(SYNCTL_CACHE_FACTOR_WARNING)
         os.environ["SYNAPSE_CACHE_FACTOR"] = str(cache_factor)
 
     cache_factors = config.get("synctl_cache_factors", {})