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https://issues.apache.org/jira/browse/CASSANDRA-21173?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18058454#comment-18058454
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Matt Byrd commented on CASSANDRA-21173:
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Snapshot loading machinery added which cannot load pre 2.1 tables without
table-id embedded in folder.
> Snapshots from tables without table-id embedded in their folder name are not
> loaded by SnapshotLoader
> -----------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21173
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21173
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/Snapshots, Local/Startup and Shutdown
> Reporter: Matt Byrd
> Assignee: Matt Byrd
> Priority: Normal
> Fix For: 5.0.x, 5.1, 6.x
>
>
> Tables created prior to 2.1 do not have a table-id embedded in their table
> folder name.
> This is handled correctly in Directories.java (see constructor) unfortunately
> in SnapshotLoader, we use a regex which attempts to extract the table-id and
> hence skips over any tables created prior to 2.1.
> The end result is that these tables are not visible in list snapshot and more
> importantly cannot be cleared via nodetool clearsnapshot. This was noticed
> upon major upgrade to 5.0.
> I've observed this on 5.0, from reading the code it appears likely improved
> in 5.1, in that it now requires a restart in addition to trigger.
> Some related tickets:
> Introduction of table-id and backwards compatible handling of old folders
> originally here:
> https://issues.apache.org/jira/browse/CASSANDRA-5202
> Machinery to list snapshots which doesn’t handle old format was added here:
> https://issues.apache.org/jira/browse/CASSANDRA-16843
> https://github.com/apache/cassandra/commit/31aa17a2a3b18bdda723123cad811f075287807d
> There was some discussion at the time of not handling pre 2.1 tables here:
> https://issues.apache.org/jira/browse/CASSANDRA-16843?focusedCommentId=17440088&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17440088
> Then nodetool clearsnapshot stopped working here with:
> https://issues.apache.org/jira/browse/CASSANDRA-17757
> Things improve a bit in 5.1 with
> https://issues.apache.org/jira/browse/CASSANDRA-18111
> Now we no longer try and load the snapshots via SnapshotLoader in entirety
> before deciding if we can clear them, but instead make use of
> SnapshotManager. Whilst snapshots taken while the jvm is running are now
> visible and clearable, from reading upon restart we lose that information and
> cannot view/clear snapshots created before the restart.
> One solution to handle these pre 2.1 tables, is to include the table-id in
> the manifest.json, then we'll be able to read this information if not
> available from folder name upon restart.
> Another possibility which doesn't fix as many problems, is just to expose via
> jmx/nodetool
> something to allow operators to bypass the snapshot loading mechanism and
> directly clear the old pre-2.1 snapshots.
> A more involved and risky change would be to somehow think about how we
> migrate all this existing data in different folder structures to new
> consistent folder structure, but this seems quite involved and would likely
> deserve it's own JIRA at least.
> I have a patch locally against trunk for the first approach, just storing the
> tableId in the manifest.json, which does this and will run it against CI.
> I'll have a further think about if there are any other approaches, if anyone
> has any ideas let me know.
> Another thing to consider is where we should apply this change.
> Probably at a minimum 5.0, since that's where one can no longer nodetool
> clearsnapshot on certain tables and the effect is a bit worse there than in
> 5.1.
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