[DISCUSS] ISSUE-1429 Refactor the Alter Table process

[陈明雨 <mo...@163.com>]

Hi all:
I'd like to propose issue 1429(https://github.com/apache/incubator-doris/issues/1429), which is to refactor the process of Alter Table.

The current process of Alter Table has following problems:


1. Slow
    Each sub task of an alter job has to wait the current running transaction to be finished before starting the task.
2. Relation chain with base tablet.
    Each new tablet created by alter job has a relation chain with its base tablet (the base tablet is where history data comes from).
    Maintaining this chain make the process very complicated.
3. FINISHING state of Alter job
    The Alter Job has a state called  FINISHING. The job in FINISHING state need to wait all current running transactions to be finished before transferring to FINISHED.
    But in some case, FINISHING may last for a very long time.


To solve these problem, I would like to refactor the Alter Table process.
More design details can be seen in Github issue #1429 



--
此致！Best Regards
陈明雨 Mingyu Chen

Email:
chenmingyu@apache.org