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https://issues.apache.org/jira/browse/CASSANDRA-17048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17434220#comment-17434220
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Jacek Lewandowski commented on CASSANDRA-17048:
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If we can agree that the upgrade is irrevocable after switching to the new
scheme, then you are right, it is much easier to implement indeed.
The question here from the usability pov - what is the default?
- if the default is to use the old scheme, we impose an additional operation
for the typical path (just upgrade)
- if the default is to use the new scheme, it will be easy to miss switching
that option and land in the place where downgrade is impossible
Implementing downgrader is far more complex that that though. We have to rename
all the newly generated files, perhaps touch the snapshots which were created
in the new version, perform modifications in system tables and eventually
compact them.
The options without downgrader seem to be valid for other system tables as
well. They do not seem to support downgrading though.
TBH - I don't know which approach we should go for.
BTW. regarding 3.0 to 4.0 - I still cannot find the part which you meant - can
you point it in the PR? I tried to just "rename" system keyspace migrator, but
given to the amount of changes git decided to remove/add it. However, I just
refactored the existing stuff (and added migration of sstable_activity).
> Replace sequential sstable generation identifier with ULID
> ----------------------------------------------------------
>
> Key: CASSANDRA-17048
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17048
> Project: Cassandra
> Issue Type: Improvement
> Components: Local/SSTable
> Reporter: Jacek Lewandowski
> Assignee: Jacek Lewandowski
> Priority: Normal
> Fix For: 4.1
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Replace the current sequential sstable generation identifier with ULID based.
> ULID is better because we do not need to scan the existing files to pick the
> starting number as well as we can generate globally unique identifiers.
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