erl_snowflake

Erlang fast snowflake id generator. Instead of others erlang snowflake libraries based on gen_servers this one uses persistent_term and atomics for counter storage. This is simple and fast.

Simple example

1> erl_snowflake:generate(b62).
<<"1X1Dr9LDBx3">>

ID formats

There are three representation formats for snowflake id:

tuple {timestamp(), machine_id(), counter()}
integer
binary
binary string
base62 binary string

1> ID = erl_snowflake:generate().
{306679254831,949,1}
2> erl_snowflake:to(bin, ID).
<<17,217,224,131,203,251,80,1>>
3> erl_snowflake:to(int, ID).
1286306025258569729
4> erl_snowflake:to(str, ID).
<<"1286306025258569729">>
5> erl_snowflake:to(b62, ID).
<<"1X1IIuWythR">>

Machine id

By default hash from hostname is used, but you can specify your own by erl_snowflake:set_machine_id/1.

1> erl_snowflake:get_machine_id().
949
2> erl_snowflake:hostname().
"asrock-x300"
3> erl_snowflake:set_machine_id(erl_snowflake:term_to_machine_id("asrock-x300-1")).
ok
4> erl_snowflake:get_machine_id().
238

ID structure

Classical twitter id structure is 41-10-12

41 timestamp
10 machine id
12 counter

It can be configured via defines for your needs (e.g. as in instagram 41-13-10).

rebar.config

{overrides, [
  {override, erl_snowflake, [
    {erl_opts, [
      % instagram id structure
      {d, timestamp_bits , 41},
      {d, machine_id_bits, 13},
      {d, counter_bits   , 10},
      {d, epoch          , 1314220021721}
    ]}
  ]}
]}.

Rollover

generate_* functions check counter rollover and generate_unsafe will throw error:'maximum counter value reached', while generate function will wait 1 ms and try again (and throw the error if second attemt will fail).

Time adjustments

If for some reasons (e.g. NTP) time will go backwards generate_* functions will throw error:'system time has gone backwards' to prevent IDs collision.

petrkozorezov/erl_snowflake