Mero is a scalable and lightweight OTP Erlang client for memcache. Mero allows interaction with different clusters, specifying different number of pools per server and sharding algorithms per cluster.
Mero achieves high-performance in a number of ways. Mero does not use an Erlang process per socket. Each pool worker adjusts the number of available sockets based on demand and sockets are shared to the point of usage, avoiding copying of terms through the system, as is present in the per-process design common in other pooling libraries. All pools are registered with a local name and its workers are created on startup, removing pool selection bottlenecks and worker creation latency.
If a connection to the memcached server fails there is a mechanism to delay connection retries. All the connections are renewed every time interval.
The storage module is configurable so you can use different protocols or even use a storage different than memcache.
It includes a callback that will be called to notify of specific error events. These events have the form of:
{Id :: list(atoms),
Args :: list([{Key :: cluster_name | host | port | error_reason,
Value :: term()}])
}
Example Ids are:
[socket, connect, ok][socket, connect, error][socket, send, error][socket, rcv, error][socket, controlling_process, error]
Please consult mero.app.src to see all the available options. The sharding
algorithms available are shard_phash2 and shard_crc32.
[{cluster_a,
[{servers, [{"server1", 11211},
{"server2", 11211},
{"server3", 11211},
{"server4", 11211},
{"server5", 11211},
{"server6", 11211},
{"server7", 11211},
{"server8", 11211}]},
{sharding_algorithm, {mero, shard_phash2}}, %% Module and function
{workers_per_shard, 3}, %% Number of pools that each server will have
{pool_worker_module, mero_wrk_tcp_txt}]
},
{cluster_b,
[{servers, [{"localhost", 11211}]},
{sharding_algorithm, {mero, shard_crc32}},
{workers_per_shard, 1},
{pool_worker_module, mero_wrk_tcp_txt}]
},
...
]
Configuration can also be implemented to support auto discovery of the cluster as opposed to hardcoding nodes. Provide the configuration endpoint (AWS Reference) and port as in the following example.
[{cluster_b,
[{servers, {elasticache, "ConfigEndpointHostname.com", PortNumber}},
{sharding_algorithm, {mero, shard_crc32}},
{workers_per_shard, 1},
{pool_worker_module, mero_wrk_tcp_binary}]
},
...
]
make
make test
There are three ways to start this application:
- From an erlang shell:
erl -pa ebin/ -pa deps/*/ebin/ -s inets -s mero
> mero:increment_counter(default, <<"key">>).
{ok,1}
> mero:increment_counter(default, <<"key">>).
{ok,2}
> mero:get(default, <<"key">>).
{<<"key">>,<<"2">>}
> mero:set(default, <<"key">>, <<"5">>, 3600, 5000).
ok
> mero:increment_counter(default, <<"key">>).
{ok,6}
> mero:set(default, <<"key">>, <<"50">>, 3600, 5000).
ok
> mero:increment_counter(default, <<"key">>).
{ok,51}
> mero:increment_counter(default, <<"key2">>).
{ok,1}
> mero:increment_counter(default, <<"key3">>).
{ok,1}
> mero:increment_counter(default, <<"key4">>).
{ok,1}
> mero:mget(default, [<<"key">>, <<"key2">>, <<"key3">>, <<"key4">>], 5000).
[{<<"key">>,<<"51">>},
{<<"key2">>,<<"1">>},
{<<"key3">>,<<"1">>},
{<<"key4">>,<<"1">>}]
> mero:set(default, <<"key">>, <<"key">>, 3600, 5000).
ok
> mero:set(default, <<"key2">>, <<"key2">>, 3600, 5000).
ok
> mero:increment_counter(default, <<"key">>).
{error,incr_decr_on_non_numeric_value}
=ERROR REPORT==== 3-Apr-2015::13:57:40 ===
error: memcached_request_failed
client: {client,#Port<0.3562>,undefined,
{mero,stat_event_callback,
[{cluster_name,default},
{host,"localhost"},
{port,11211}]}}
cmd: {5,{<<"key">>,<<"1">>,<<"1">>,<<"86400">>}}
reason: incr_decr_on_non_numeric_value
> mero:mget(default, [<<"key">>, <<"key2">>, <<"key3">>, <<"key4">>], 5000).
[{<<"key">>,<<"key">>},
{<<"key2">>,<<"key2">>},
{<<"key3">>,<<"1">>},
{<<"key4">>,<<"1">>}]
> mero:flush_all(default).
[{default,ok}]
> mero:mget(default, [<<"key">>, <<"key2">>, <<"key3">>, <<"key4">>], 5000).
[{<<"key">>,undefined},
{<<"key2">>,undefined},
{<<"key3">>,undefined},
{<<"key4">>,undefined}]
> mero:add(default, <<"key">>, <<"value">>, 1000, 5000).
ok
> mero:add(default, <<"key">>, <<"value">>, 1000, 5000).
{error,already_exists}
=ERROR REPORT==== 3-Apr-2015::14:03:25 ===
error: memcached_request_failed
client: {client,#Port<0.3558>,undefined,
{mero,stat_event_callback,
[{cluster_name,default},
{host,"localhost"},
{port,11211}]}}
cmd: {2,{<<"key">>,<<"value">>,<<"1000">>}}
reason: already_exists
> {mero:madd(default, [{<<"foo">>, <<"bar">>, 1000},
{<<"bar">>, <<"foo">>, 1000},
{<<"foo">>, <<"baz">>, 1000}], 5000),
mero:mget(default, [<<"foo">>, <<"bar">>], 5000)}.
{[ok,ok,{error,already_exists}],
[{<<"bar">>,<<"foo">>},{<<"foo">>,<<"bar">>}]}
> mero:mcas(default, [{<<"xyzzy">>, <<"bar">>, 0, 360391},
{<<"qwer">>, <<"asdfsdf">>, 0, 360390}], 5000).
[ok,{error,already_exists}]
-
Set the configuration in the mero.app.src file and start the application inside your OTP node.
-
As an OTP included application, pass the ClusterConfiguration as a parameter to the supervisor of the application.
mero_sup:start_link([{default,[{servers,[{"localhost",11211}]},
{sharding_algorithm,{mero,shard_crc32}},
{workers_per_shard,1},
{pool_worker_module,mero_wrk_tcp_txt}]}]).
Warning: This will erase all the contents of the memcached server it connects to ("localhost" by default). Uncomment the test cases at suite test/mero_test_with_local_memcached_SUITE.erl