Re: POC and rebased patch for CSN based snapshots

On 2020/06/19 13:36, movead.li@highgo.ca wrote:
> 
>  >You mean that the last generated CSN needs to be WAL-logged because any smaller
>>CSN than the last one should not be reused after crash recovery. Right?
> Yes that's it.
> 
>>If right, that WAL-logging seems not necessary because CSN mechanism assumes
>>CSN is increased monotonically. IOW, even without that WAL-logging, CSN afer
>>crash recovery must be larger than that before. No?
> 
> CSN collected based on time of  system in this patch, but time is not reliable all the
> time. And it designed for Global CSN(for sharding) where it may rely on CSN from
> other node , which generated from other machine.
> 
> So monotonically is not reliable and it need to keep it's largest CSN in wal in case
> of crash.

Thanks for the explanaion! Understood.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION