Support Saga Transaction

[tuohai666]

What's Saga?
The paper:
https://www.cs.cornell.edu/andru/cs711/2002fa/reading/sagas.pdf
The github project which Sharding-Sphere will integrate with:
https://github.com/apache/incubator-servicecomb-saga
More information from Willem Jiang's presentation:
http://servicecomb.incubator.apache.org/cn/docs/distributed-transactions-saga-implementation/

The second soft transaction (i.e. flexible transaction) which Sharding-Sphere will support is Saga transaction. In the first step, we plan to implement it in Sharding-JDBC.

SS starts a transaction via Saga API(https://github.com/apache/incubator-servicecomb-saga/blob/old-saga/docs/api/api.md). The API looks like this:
{
"policy": "",
"requests": [
{
"id": "",
"type": "",
"serviceName": "",
"parents": [
],
"transaction": {
"method": "",
"path": "",
"params": {
}
},
"compensation": {
"method": "",
"path": "",
"params": {
}
}
}
]
}
Logic SQLs in a SS transaction will be treated as one Saga Request separately. Users of SS should supply the compensatory SQLs correspondingly:
transaction:
INSERT INTO t_order (order_id, user_id, status) VALUES (?, '10', 'INIT');
compensation:
DELETE FROM t_order WHERE order_id=?;
SS need to implement method of both transaction and compensation for Saga. The path parameter seems to have no use for SS, and should be ignored.
The content of params should include SQL and the parameter of SQL, may implement by currently form parameters.
At last, id and serviceName will be generated by SS uniquely. Saga can use these identifier to find transactions.

[KomachiSion]

In the previous description, Sharding-Sphere uses Service Comb Saga's Restful API to implement saga transactions. But SS would like to use saga coordinator in an internal call.
After discussing with Service Comb, Service Comb Saga will extend some interfaces so that SS can call the saga coordinator internally.
Related issue: https://issues.apache.org/jira/browse/SCB-864

[KomachiSion]

SS also starts transaction via Saga API https://github.com/apache/incubator-servicecomb-saga/blob/master/docs/api/api.md .
The new API looks like:

{
  "policy": "",
  "requests": [
    {
      "id": "",
      "type": "",
      "datasource": "",
      "parents": [

      ],
      "transaction": {
        "sql": "",
        "params": [
          []
        ]
      },
      "compensation": {
        "sql": "",
        "params": [
          []
        ]
      }
    }
  ]
}

Logic SQLs in a transaction will be parsed and routed, and will be combined into a graph.
This graph will be mapped to saga API json and invoke saga coordinator to execute saga transaction.

[KomachiSion]

TODO list of saga transaction:

• Integrate Service Comb Saga
  • Build saga request from SQLs in transaction
  • Invoke Service Comb Saga in SagaTransactionManager
• Sharding-JDBC support Saga
  • Support JDBC statement
  • Support JDBC preparedStatement
  • Support JDBC BatchPreparedStatement
• Sharding-Proxy support Saga
  • Support Proxy JDBC backend
• Support different recover policy
  • Support forward recover policy
    • Configure the max retires
  • Support backward recover policy
    • Generate revert SQL
• Persistent Store Saga transaction logs
• Configure Saga params
  • Configure in Sharding-JDBC
    • Init configuration
    • Renew configuration
  • Configure in Sharding-Proxy
    • Init configuration
    • Renew configuration
• Examples
  • Example for Sharding-JDBC
  • Example for Sharding-Proxy