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https://issues.apache.org/jira/browse/CASSANDRA-16063?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17210517#comment-17210517
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Ekaterina Dimitrova commented on CASSANDRA-16063:
-------------------------------------------------

Thanks [~adelapena]

I believe all your comments were addressed.

I only didn't return the test as I noticed that [~slebresne] created In-jvm 
test as part of his work for  CASSANDRA-15897.  

My suggestion is to not add it back for now and continue that topic in the 
other ticket. I am almost 99% sure we will utilize his test at the end.

> Fix user experience when upgrading to 4.0 with compact tables
> -------------------------------------------------------------
>
>                 Key: CASSANDRA-16063
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16063
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Legacy/CQL
>            Reporter: Sylvain Lebresne
>            Assignee: Ekaterina Dimitrova
>            Priority: Normal
>             Fix For: 4.0-beta
>
>         Attachments: Compact_storage_upgrade_tests.txt
>
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> The code to handle compact tables has been removed from 4.0, and the intended 
> upgrade path to 4.0 for users having compact tables on 3.x is that they must 
> execute {{ALTER ... DROP COMPACT STORAGE}} on all of their compact tables 
> *before* attempting the upgrade.
> Obviously, some users won't read the upgrade instructions (or miss a table) 
> and may try upgrading despite still having compact tables. If they do so, the 
> intent is that the node will _not_ start, with a message clearly indicating 
> the pre-upgrade step the user has missed. The user will then downgrade back 
> the node(s) to 3.x, run the proper {{ALTER ... DROP COMPACT STORAGE}}, and 
> then upgrade again.
> But while 4.0 does currently fail startup when finding any compact tables 
> with a decent message, I believe the check is done too late during startup.
> Namely, that check is done as we read the tables schema, so within 
> [{{Schema.instance.loadFromDisk()}}|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/service/CassandraDaemon.java#L241].
>   But by then, we've _at least_ called 
> {{SystemKeyspace.persistLocalMetadata()}}} and 
> {{SystemKeyspaceMigrator40.migrate()}}, which will get into the commit log, 
> and even possibly flush new {{na}} format sstables. As a results, a user 
> might not be able to seemlessly restart the node on 3.x (to drop compact 
> storage on the appropriate tables).
> Basically, we should make sure the check for compact tables done at 4.0 
> startup is done as a {{StartupCheck}}, before the node does anything.
> We should also add a test for this (checking that if you try upgrading to 4.0 
> with compact storage, you can downgrade back with no intervention whatsoever).



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