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https://issues.apache.org/jira/browse/CASSANDRA-21173?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18063478#comment-18063478
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Stefan Miklosovic commented on CASSANDRA-21173:
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1) I do not think that doing this for anything but trunk is a good idea
2) The main reason you are doing this is that you have 2a .x node with
snapshots without table id in a directory name and you are upgrading. That is
the only reason you are trying to introduce table id into the manifest, apart
from that, that "code path" is not normally exercised. In the context of newer
branches, snapshots without table id in a directory name are invalid. I am not
sure we should accommodate the code just for this corner case which comes from
times of 2.x.
3) My concerns are that this might bring some compatibility issues when you
introduce table id into manifest like that. However, thinking about it more, we
have "ignore unknown properties" in the DTO when we deserialize JSON with that
field into that object, so it _should_ work, but it would be nice to have some
test around that
4) My preferred way of dealing with this is that when a node starts, it will
scan the snapshots, they are loaded right now by SnapshotManager. What we could
do is to scan it even before that, identify snapshots which do not have ID in
them, and rename these directories to contain table ids. Then SnapshotManager
loading logic does not need to change and all snapshots will contain table id
in their directory paths, as it should be.
We might indeed entertain the idea of introducing table id into a manifest, or
modify the content of manifest to contain way more information (hashes of
files, their sizes ...), and yes, table id as well, but the enrichment of
manifest.json like that needs a completely separate discussion which should
happen independently from your necessity to load older snapshots into a newer
node.
> 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
>
> Attachments: ci_summary_trunk_mbyrd_CASSANDRA-21173.html
>
>
> 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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