shard range cache can get too big for memcache

The default max size for values in memcache is 1MB

https://cloud.google.com/memorystore/docs/memcached/memcached-configs

we've seen shard ranges responses larger than that on sharded dbs with >3K shard ranges

In my experiments when setting a value larger than 1MB using our memcache client no errors are reported, but the value is not cached which can overrun the root container db with GET requests to fetch the shard ranges.

we were able to work around the issue by increasing the max value in memcache

But larger values may not be ideal; we should consider documenting the recommended configuration tweak or breaking shard range caching into multiple keys (compression may be another option)