Khepri 0.2.0

At this point, Khepri should be considered Alpha and not production ready. The API will likely evolve and future releases will likely introduce breaking changes. The goal of this release is to make it easy for anyone to try it and possibly give feedback.

What's new in Khepri 0.2.0

Stored procedures and triggers

This version introduces stored procedures and triggers. They allow to store code in the database itself and automatically execute it after some event occurs.

1. Store an anonymous function in the tree:

   StoredProcPath = [path, to, stored_procedure],
   
   Fun = fun(Props) ->
             #{path := Path},
               on_action => Action} = Props
         end,
   
   khepri_machine:put(
     StoreId,
     StoredProcPath,
     #kpayload_sproc{sproc = Fun}))}.

2. Register a trigger using an event filter:

   EventFilter = #kevf_tree{path = [stock, wood, <<"oak">>]},
   
   ok = khepri_machine:register_trigger(
          StoreId,
          TriggerId,
          EventFilter,
          StoredProcPath))}.

In the example above, as soon as the [stock, wood, <<"oak">>] node is created, updated or deleted, the anonymous function will be executed.

See #47.

Use records to describe payloads instead of macros

Payloads are now described as Erlang records. This allows to benefit from more compile-time checks in particular.

Here are the modifications you will have to do in your code:

% Up until 0.1.1:
khepri_machine:put(StoreId, Path, ?DATA_PAYLOAD(Data)).

% Starting from 0.2.0:
khepri_machine:put(StoreId, Path, #kpayload_data{data = Data}).

See #20.

keep_until conditions renamed to keep_while

The keep_until option of khepri_machine:put/3 was renamed to keep_while. The reason is that the tree node is kept while the condition is met. As soon as the condition evaluates to false, the tree node is deleted.

Here are the modifications you will have to do in your code:

% Up until 0.1.1:
khepri_machine:put(StoreId, Path, Payload, #{keep_until => #{Path => Condition}}).

% Starting from 0.2.0:
khepri_machine:put(StoreId, Path, Payload, #{keep_while => #{Path => Condition}}).

See #18.

Stacktrace frames pointing to an extracted function code have line numbers

Before, when a transaction function encountered an exception, the stacktrace would miss the source file and line number for frames pointing to the extracted code:

%% Based on the following function:
%%     crashing_fun() ->
%%         throw("Expected crash").

1> Fun = khepri_fun:to_standalone_fun(fun mod:crashing_fun/0, #{}).
2> khepri_fun:exec(Fun, []).
** exception throw: "Expected crash"
     in function  kfun__mod__crashing_fun__33048370:run/0

Now, khepri_fun decode lines information and the stacktrace frames provide the source file and the line number:

1> Fun = khepri_fun:to_standalone_fun(fun mod:crashing_fun/0, #{}).
2> khepri_fun:exec(Fun, []).
** exception throw: "Expected crash"
     in function  kfun__mod__crashing_fun__33048370:run/0 (.../mod.erl, line 30)

See #51.

Other changes

• Ra was updated from 2.0.2 to 2.0.4.
• Several functions of the re Erlang module are allowed in transaction functions (#41).
• Patch several assembly instructions incorrectly decoded by beam_disasm (#39).
• Many new assembly instructions supported in the function extraction code.
• Annotate registers with type information to fix compilation failures related to function extracted (#36, #49).
• The workaround to make it possible to run Dialyzer on testsuite was removed (#23). Now, one just has to use rebar as test dialyzer.
• Modules to generate the nicer documentation were moved to https://hex.pm/packages/rebar3_edoc_extensions.

Download

Khepri 0.2.0 is available from Hex.pm: https://hex.pm/packages/khepri/0.2.0

Upgrade

Using Rebar:

1. Update your rebar.config:

   %% In rebar.config
   {deps, [{khepri, "0.2.0"}]}.

2. Run rebar3 upgrade khepri.

Using Erlang.mk:

1. Update your Makefile:

   %% In your Makefile
   dep_khepri = hex 0.2.0

2. Remove the deps/khepri directory. The new version will be fetched the next time you build your project.

Documentation

The documentation for Khepri 0.2.0 is available on Hex.pm.

Contributors

A warm thank you to contributors outside of the RabbitMQ team, this is invaluable for such a young project!

• Michael Davis (@the-mikedavis)
• Viacheslav Katsuba (@vkatsuba)