Smooth upgrade（incompatible version）

[needkane]

Smooth upgrade（incompatible version）

[metabd]

incompatible upgrade problems:

1. data strcuture incompatible:
   (1)transaction type or block type changed ,added or deleted some fieled
   (2)added or deleted some data type
   may be have these problems when upgrading:
   (1) load old data fail
   (2) verifying fail ,verifing consensus and other requirements
   (3) sync data , produced new block and some nodes are not upgrade yet

solution :
versioning ? change any data field upgrade version and remain old version code ?

after all nodes upgrating , node also can rewrite data with new version.

2.p2p communication protocol or data changed
p2p protocol or data changes , some node use old data structure and some use new data structure ,how to solve this ?
versioning , after a now upgreade , send old version data and swap it's version , then if another node upgrade ,they will communicate in new protocol or new version data

3. rpc api changes
   versioning :
   old version api process old data , new version api process new version data。
   old : /api/...
   new: /api/v2/...