caiconghui commented on pull request #5925:
URL: https://github.com/apache/incubator-doris/pull/5925#issuecomment-849659166


   > SegmentV1 will be deprecated in the future, so I don't think this change 
is necessary.
   > Insisting on maintaining SegmentV1 will be a big burden in future 
vectorization support
   
   Yes , I agree with you that SegmentV1 will be deprecated in the future, 
segment V2 will replace all segment v1 in the future.
   
   This PR is not Insisting on maintaining SegmentV1 but to be compatible with 
older doris version.
   
   For new doris user , This PR doesn't take any effect, all newer table will 
be created by segment v2
   
   For older doris user, there are many tables with segment v1, and it need to 
gradually change V1 to v2,
   actually, for many older doris user, the most important thing is stable on 
production enviroment, but now, Very few alter operations succeed, most fail 
due to timeout, because convert v1 to v2 is a huge task which would cost a lot 
of time while there are many tablets in older table. and once timeout,  all 
operations that convert v1 to v2 would rollback, which is not what we expect, 
and make doris not friendly to older user
   
   If we always alter table failed,  it is meanless to  convert v1 to v2 when 
do alter table, I think it is not a good idea to convert v1 to v2 when user 
just want to add column for table, which now seems an impossible goal to achive


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