Basic Brick API: Basic UBF Data Types

table()           = atom(nonempty,nonundefined);
key()             = binary();
%% ts = timestamp = usually an int64: time_t * 1000000 + usecs
ts()              = integer();
val()             = binary();
exp_time()        = time_t();
flags_list()      = [do_op_flag()];
do_op_flag()      = {testset, ts()} |
                    witness |
                    get_all_attribs |
                    %% Flags for get_many
                    {max_num, integer()} |
                    {binary_prefix, binary()} |
                    must_exist |
                    must_not_exist |
                    value_in_ram |
                    ....

Basic Brick API: modify ops

add()             = {add,     key(), ts(), val(), exp_time(), flags_list()};
replace()         = {replace, key(), ts(), val(), exp_time(), flags_list()};
set()             = {set,     key(), ts(), val(), exp_time(), flags_list()};

add_res()         = do1_res_ok() | do1_res_fail();

do1_res_ok()      = ok |
                    key_not_exist |
                    {ok, ts()} |
                    {ok, ts(), val()} |
                    ....

do1_res_fail()    = {key_exists, ts()} |
                    key_not_exist |
                    {ts_error, ts()} |
                    invalid_flag_present |
                    %% The responsible brick is unavailable/crashed/whatever.
                    brick_not_available;

Basic Brick API: read-only ops

get()             = {get,      key(), flags_list()};
get_many()        = {get_many, key(), flags_list()};

get_res()         = key_not_exist |
                    {ok, ts()} |
                    {ok, ts(), val()} |
                    {ok, ts(), val(), time_t(), flags_list()}
                    ....
get_many_res() = {ok, {[{key(), ts()}], boolean()}} |
                 {ok, {[{key(), ts(), flags_list()}], boolean()}} |
                 {ok, {[{key(), ts(), val(), time_t(), flags_list()}], boolean()}} |

• Witness minimize wire transfer of redundant data for quorum reads.
• All the building blocks for a robust quorum-style replication system
• ... except that multi-key transactions are messy with multiple writers.
  • ... unless you have more stuff, like a transaction manager.

  ---

  Middle Layer: chain replication

  Diagrams!

  

  ---

  Top Layer: consistent hashing

  

  ---

  

  ---

  ---

  Hibari Tables

  CREATE TABLE foo (
    BLOB key;
    BLOB value;
    INTEGER timestamp;
    INTEGER expiration_time;        -- 0 = no expiry
    ERLANG_PROPERTY_LIST proplist;  -- Usually empty
  ) UNIQUE PRIMARY KEY key;
  

  ---

  

  ---

  Data Migrations

• Change chain length (a.k.a. change replication factor)
• Add chains (with or without adding new hardware)
• Remove chains (with or without adding new hardware)
• Reweight chains

Micro-Transactions

• Original chain replication paper: head of chain can make non-deterministic decisions

Valid micro-transaction: all keys managed by same chain

    [txn,
     {op = replace, key = "string1", value = "Hello, world!"},
     {op = delete, key = "string4"}
    ]

Invalid micro-transaction: keys managed by different chains

    [txn,
     {op = replace, key = "string1", value = "Hello, world!"},
     {op = delete, key = "string2"}
    ]

Actually Useful Micro-transactions

• {TableName, KeyPrefix} -> Chain
• Key prefix is sort-of like a Riak "bucket"
• Key prefix method configurable per table
  • Everything: <<"whole-key-whatever">>
  • Fixed length prefix: <<Prefix:4/binary, "whatever">>
  • Variable length prefix (e.g. to Nth slash): <<"@slfritchie/whatever">>

Example Micro-Transaction

Imagine a table called 'posts'

add_new_post(UserID, PostText) ->
  Prefix = "/" ++ integer_to_list(UserID) ++ "/",
  MetaKey = Prefix ++ "summary",
  {ok, OldTS, OldVal} = brick_simple:get(posts, MetaKey),

  #post{next_id = NextID, active = Active} =
      OldMeta = binary_to_term(OldVal),
  PostKey = Prefix ++ integer_to_list(NextID),
  NewMeta = OldMeta#post{next_id = NextID + 1,
                         active = Active + 1},

  %% replace op: Abort if the key does not exist
  %%             or if current timestamp /= OldTS.
  %% add op: Abort if the key already exists.
  Txn = [brick_server:make_txn(),
         brick_server:make_replace(MetaKey, term_to_binary(NewMeta),
                                   0, [{testset, OldTS}]),
         brick_server:make_add(PostKey, PostText)],
  [ok, ok] = brick_simple:do(posts, Txn).

The Admin Server