TCC of distributed solutions

summary

What is? TCC Business

TCC yes Try、Confirm、Cancel Abbreviations of three words ,TCC Each branch transaction is required to implement three operations ： Preprocessing Try、 confirm Confirm、 revoke Cancel.Try Do business check and resource reservation ,Confirm Do business confirmation ,Cancel To achieve a relationship with Try The reverse operation is the rollback operation .TM Initiate all branch transactions first try operation , Of any branch transaction try Operation execution failed ,TM Will initiate all branch transactions Cancel operation , if try The operation was all successful ,TM Will initiate all branch transactions Confirm operation , among Confirm/Cancel If the operation fails ,TM Will try again .

TCC There are three stages ：

1. Try The stage is to do business inspection （ Uniformity ） And resource reservation （ Isolation ）, This stage is only a preliminary operation , It and the following Confirm Together to really form a complete business logic .
2. Confirm The stage is to make a confirmation submission ,Try Start execution after all branch transactions of phase are executed successfully Confirm. Usually , use TCC Think Confirm There is no mistake in the stage . namely ： Only Try success ,Confirm It must be successful . if Confirm The stage really went wrong , Need to introduce retry mechanism or manual processing .
3. Cancel The phase is to cancel the branch transaction when the business execution error needs to be rolled back , Reserve resource release . Usually , use TCC Think Cancel Stage is also a certain success . if Cancel The stage really went wrong , Need to introduce retry mechanism or manual processing .
4. TM Business management
   TM The transaction manager can be implemented as a stand-alone service , You can also have the global transaction initiator act as TM Role ,TM Independent to be a common component , In order to consider the system structure and software reuse .
   TM Generate a global transaction record when initiating a global transaction , Global transaction ID Throughout the chain of distributed transaction calls , Used to record transaction context , Track and record status , because Confirm and Cancel Failure needs to be retried , So we need to be idempotent , Idempotency refers to the same operation, no matter how many times it is requested , The results are the same .

TCC Solution

Currently on the market TCC There are many frameworks, such as the following ：
（ The following data collection date is 2019 year 07 month 11 Japan ）
tcc-transaction：https://github.com/changmingxie/tcc-transaction
Hmily：https://github.com/dromara/hmily
ByteTCC：https://github.com/liuyangming/ByteTC
EasyTransaction：https://github.com/QNJR-GROUP/EasyTransaction
What was said in the previous section Seata Also support TCC, but Seata Of TCC Pattern configuration is relatively complex . Our goal is to understand TCC And the process of coordinated operation of affairs , So it's more of a lightweight, easy to understand framework , So... Was finally determined Hmily.
Hmily It's a high-performance distributed transaction TCC Open source framework . be based on Java Language to develop （JDK1.8）, Support Dubbo,Spring Cloud etc. RPC Framework for distributed transactions . It currently supports the following features ：

• Support nested transactions （Nested transaction support）.
• use disruptor The framework reads and writes transaction logs asynchronously , And RPC There is no difference in the performance of the framework .
• Support SpringBoot-starter Project start , Easy to use .
• RPC Framework support ：dubbo,motan,springCloud.
• Local transaction storage support ：redis,mongodb,zookeeper,file,mysql.
• Transaction log serialization support ：java,hessian,kryo,protostuff.
• use Aspect AOP To think in a face-to-face way Spring Seamless integration , Natural support cluster .
• RPC Transaction recovery , Timeout abnormal recovery, etc .
  Hmily utilize AOP Intercept local and remote methods involved in distributed transactions , By intercepting , Transaction participants can transparently call the Try、Confirm、Cancel Method ; Pass transaction context ; And record the transaction log , Make compensation as appropriate , Retry etc. .
  Hmily There is no need for transaction coordination services , But you need to provide a database （mysql/mongodb/zookeeper/redis/file） To store logs .
  Hmily Realized TCC Service is the same as ordinary service , Just expose one interface , That's what it is Try Business .Confirm/cancel Business logic , Just because of global transaction commit / Rollback needs to be provided , therefore Confirm/Cancel Business only needs to be Hmily TCC Transaction framework discovery . It doesn't need to be perceived by other business services that call it .
  website ：https://dromara.org/website/zh-cn/docs/hmily/index.html

TCC Note that the three exception handling methods are null rollback 、 idempotent 、 Hang

Empty rollback

idempotent

Hang