Updates to docker-entrypoint for worker and scheduler (#364)

* Use --max-tasks-per-child as per celery documentation

* Set --max-memory-per-child to 1/4th of total system memory

* Split exec command over multiple lines

* Fix memory variable typo

bin/docker-entrypoint

@@ -5,9 +5,13 @@ worker() {
   /app/manage.py db upgrade
   WORKERS_COUNT=${WORKERS_COUNT:-2}
   QUEUES=${QUEUES:-queries,scheduled_queries,celery}
+  MAX_MEMORY=$(($(/usr/bin/awk '/MemTotal/ {print $2}' /proc/meminfo)/4))
 
   echo "Starting $WORKERS_COUNT workers for queues: $QUEUES..."
-  exec /usr/local/bin/celery worker --app=redash.worker -c$WORKERS_COUNT -Q$QUEUES -linfo --maxtasksperchild=10 -Ofair
+  exec /usr/local/bin/celery worker --app=redash.worker -c$WORKERS_COUNT -Q$QUEUES -linfo \
+      --max-tasks-per-child=10 \
+      --max-memory-per-child=$MAX_MEMORY \
+      -Ofair
 }
 
 scheduler() {
@@ -17,7 +21,9 @@ scheduler() {
 
   echo "Starting scheduler and $WORKERS_COUNT workers for queues: $QUEUES..."
 
-  exec /usr/local/bin/celery worker --app=redash.worker --beat -c$WORKERS_COUNT -Q$QUEUES -linfo --maxtasksperchild=10 -Ofair
+  exec /usr/local/bin/celery worker --app=redash.worker --beat -c$WORKERS_COUNT -Q$QUEUES -linfo \
+      --max-tasks-per-child=10 \
+      -Ofair
 }
 
 server() {