# Mcc (Mnesia Cluster Cache)
[](https://travis-ci.com/ArcBlock/mcc)
[](https://hex.pm/packages/mcc)
`mcc` is Mnesia Cluster Cache, which support expiration and cluster.
## usage
There are some steps to use mcc:
- define table
- define model
- start expiration process
### define table
Mcc support expiration and each table need one assistant table to store expiration information.
```elixir
use Mcc.Model.Table,
table_opts: [
type: :set,
ram_copies: [node()],
storage_properties: [
ets: [:compressed, read_concurrency: true]
]
],
expiration_opts: [
expiration_table: AccountExp,
main_table: MccTest.Support.Table.Account,
size_limit: 100,
# 300M
memory_limit: 300
]
defstruct([:id, :user_profile], true)
```
Like above table definition, the `table_opts` is from [mnesia create table](http://erlang.org/doc/man/mnesia.html#create_table-2). And `expiration_opts` has several option:
- expiration_table
which table to store expiration information
- main_table
current table
- size_limit
the table size limit
- memory_limit
the memory usage limit, unit is `mega byte`
After define the table, need define the fields for the table, user can use `defstruct/1,2` to define the table's fields. Multi-fields use `[]` to organize, and fields should use `atom`. The second parameter for `defstruct` is represent if use cache expiration mechanism.
For the assistant table, the definition will be like:
```elixir
defmodule MccTest.Support.Table.Account.Exp do
@moduledoc """
Table for expiration Account table.
"""
use Mcc.Model.Table,
table_opts: [
type: :ordered_set,
ram_copies: [node()],
storage_properties: [
ets: [:compressed, read_concurrency: true]
]
]
defstruct [:key, :value]
def put(key, value) do
put(%__MODULE__{key: key, value: value})
end
end
```
## define model
After define table, user need to define model, it's not difficult:
```elixir
defmodule MccTest.Support.Cache do
@moduledoc """
Definition for cache test.
"""
use Mcc.Model
import_table(MccTest.Support.Table.Account.Exp)
import_table(MccTest.Support.Table.Account)
end
```
define model is import the tables which defined before.
## start expiration process
`mcc` use one long-lived process to scan the mnesia table for expiration. User(application) need to start the process explicitly:
```elixir
MccTest.Support.Cache.start_expiration_process()
```
Generally speaking, it will be put into application start.
[One complete example could be found in the test cases]
## Change log
- [v1.0.1]
- Fixed bug when put with ttl and remove `delete_object/1`
[pull request](https://github.com/ArcBlock/mcc/pull/6)
- [v1.0.2]
- try to connect kernel optional nodes before join cluster
- added log after joined in cluster and create/copy table
[pull request](https://github.com/ArcBlock/mcc/pull/7)
- [v1.0.3]
- support different level for operation consistency
- remove `delete/2` function, will delete expiration table automatically
- need not pass `cache_time` when put record, will calculate `now` real-time
FYI: [operation consistency for Mnesia](http://erlang.org/doc/apps/mnesia/Mnesia_chap4.html)
[pull request](https://github.com/ArcBlock/mcc/pull/8)
- [v1.1.0]
- support split mcc cluster from the logic service
- added two examples to present how to use mcc
pull requests:
- https://github.com/ArcBlock/mcc/pull/12
- https://github.com/ArcBlock/mcc/pull/5
- https://github.com/ArcBlock/mcc/pull/10
- https://github.com/ArcBlock/mcc/pull/9
- https://github.com/ArcBlock/mcc/pull/11
closed issues:
- https://github.com/ArcBlock/mcc/issues/4
