MariaDB: avoid synchronization in state configmap updates

Each MariaDB instance updates the grastate configmap on a periodic
basis, every 10s by default. Collisions can occur when multiple
instances try to write their state at the same time (within a few
milliseconds). One instance will write successfully, and the other will
get a 409 error. There is nothing to break the synchronization, so the
failures tend to be persistent.

This change adds a small sleep after a collision is encountered,
creating an offset between the cycles.

Change-Id: Ib8a64f8f7ee15a6579e901d80ae759c38e0e901e

mariadb/templates/bin/_start.py.tpl

@@ -327,6 +327,10 @@ def safe_update_configmap(configmap_dict, configmap_patch):
             # This status code indicates a collision trying to write to the
             # config map while another instance is also trying the same.
             logger.warning("Collision writing configmap: {0}".format(error))
+            # This often happens when the replicas were started at the same
+            # time, and tends to be persistent. Sleep briefly to break the
+            # synchronization.
+            time.sleep(1)
             return True
         else:
             logger.error("Failed to set configmap: {0}".format(error))