Module python-memcached uses memcache ability to add meta-data (flags) to store type of data, and uses it for parsing.

For example it sets flags=0x1 to say that data is pickled and should be unpickled.

Kestrel silently drops flags so meta-data is lost which leads us to unexpected behavior: we write python tuple "(1000, 100)", we get "(I1000
I100
tp1
." as a result.

As far as I understand Kestrel code, to achieve this functionality we should:

1. add .flags member to QItem
2. move instantiation of QItem from PersistentQueue.add to KestrelHandler.set
3. use item.flags in formatting response in KestrelHandler.get

If these are acceptable changes I'm going to code them and present patch for review shortly.

The memcache protocol allows you set a flag byte during a set, kestrel ignores this and defaults it to 0.

Many languages uses a flag to denote the data is serialized so that the client can then deserialize it.

There's proof out there that the gap in performance between the text based protocol and the binary one widens with more concurrently connected clients.

The binary protocol also has and will continue to have more clients available for it which helps kestrel's adoption.

I'm not sure if this is something to add into Kestrel itself, but tight Nagios integration would be a huge plus :)

It seems that Kestrel (1.2) doesn't reliably respond with stats when asked, for example, using my Python memcached client I call get_stats() (sends the "stats" command) which sporadically returns results, i.e.:

>>> pprint(c.get_stats())
[('127.0.0.1:22133 (1)',
  {'bytes': '0',
   'bytes_read': '12',
   'bytes_written': '1745',
   'cmd_get': '0',
   'cmd_peek': '0',
   'cmd_set': '0',
   'curr_connections': '1',
   'curr_items': '0',
   'get_hits': '0',
   'get_misses': '0',
   'queue_MapUrl_age': '0',
   'queue_MapUrl_bytes': '0',
   'queue_MapUrl_discarded': '0',
   'queue_MapUrl_expired_items': '0',
   'queue_MapUrl_items': '0',
   'queue_MapUrl_logsize': '8798',
   'queue_MapUrl_mem_bytes': '0',
   'queue_MapUrl_mem_items': '0',
   'queue_MapUrl_open_transactions': '0',
   'queue_MapUrl_total_items': '34',
   'queue_MapUrl_waiters': '0',
   'queue_Recompute_age': '0',
   'queue_Recompute_bytes': '0',
   'queue_Recompute_discarded': '0',
   'queue_Recompute_expired_items': '0',
   'queue_Recompute_items': '0',
   'queue_Recompute_logsize': '591',
   'queue_Recompute_mem_bytes': '0',
   'queue_Recompute_mem_items': '0',
   'queue_Recompute_open_transactions': '0',
   'queue_Recompute_total_items': '3',
   'queue_Recompute_waiters': '0',
   'queue_default_age': '0',
   'queue_default_bytes': '0',
   'queue_default_discarded': '0',
   'queue_default_expired_items': '0',
   'queue_default_items': '0',
   'queue_default_logsize': '0',
   'queue_default_mem_bytes': '0',
   'queue_default_mem_items': '0',
   'queue_default_open_transactions': '0',
   'queue_default_total_items': '0',
   'queue_default_waiters': '0',
   'queue_kestrel.log_age': '0',
   'queue_kestrel.log_bytes': '0',
   'queue_kestrel.log_discarded': '0',
   'queue_kestrel.log_expired_items': '0',
   'queue_kestrel.log_items': '0',
   'queue_kestrel.log_logsize': '0',
   'queue_kestrel.log_mem_bytes': '0',
   'queue_kestrel.log_mem_items': '0',
   'queue_kestrel.log_open_transactions': '0',
   'queue_kestrel.log_total_items': '0',
   'queue_kestrel.log_waiters': '0',
   'time': '1259186080',
   'total_connections': '2',
   'total_items': '0',
   'uptime': '443',
   'version': '1.2'})]
>>> pprint(c.get_stats())
[('127.0.0.1:22133 (1)', {})]

I've jumped into the debugger and it looks like Kestrel just isn't returning anything to the command.

It seems that kestrel does not work properly on uniprocessor boxes, as maxThreads is initialized to 2, and a sanity check fails inside ThreadPoolExecutor in the actors library. The condition is maximumPoolSize < corePoolSize. corePoolSize is derived from minNumThreads which is initialized to 4 statically in FJTaskScheduler2.scala.

I've fixed it in my tree, here:
http://github.com/hugohallqvist/kestrel/commit/35b2999636c0835c7b8b94d69b8af6cfd5ed0920