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https://issues.apache.org/jira/browse/CASSANDRA-17473?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17511417#comment-17511417
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James Brown commented on CASSANDRA-17473:
-----------------------------------------
While {{--hard-dereference}} is definitely cargo-culted from some other script
(and can be removed), I doubt it's at fault. It is, of course, impossible on a
POSIX system to find out what the "target" of a hardlink is (without walking
the entire filesystem's directory tree and building a reverse map of
inode->dirent), since it's just a ddirentent pointing to the same inode as
another dirent; as far as I know (and [this random Stack Overflow post
confirms|https://unix.stackexchange.com/questions/43037/dereferencing-hard-links]),
{{--hard-dereference}} merely prevents tar from deduplicating hardlinks that
are in the backup set.
> sstables changing in snapshots
> ------------------------------
>
> Key: CASSANDRA-17473
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17473
> Project: Cassandra
> Issue Type: Bug
> Reporter: James Brown
> Priority: Normal
>
> We use cassandra snapshots and tar to make full backups of our cassandra
> clusters. Sometimes, tar fails with a message like
> {{tar:
> data/addresses/addresses-eb0196100b7d11ec852b1541747d640a/snapshots/backup20220318183708/nb-167-big-Data.db:
> file changed as we read it}}
> This is kind of strange, since we're reading from a snapshot.
> The (very simplified) relevant snippet looks roughly like
> {code:java}
> nice nodetool "${JMX_ARGS[@]}" snapshot -t "$TAG" "${KEYSPACES[@]}"
> tar --hard-dereference -czpf data///snapshots/"$TAG"/{code}
> This happens maybe 1% of the time when taking backups.
> There are no concurrent snapshots going on, but there are concurrent
> compactions and repairs, of course. If it matters, this cluster _is_ running
> incremental repairs.
> This is on Cassandra 4.0.3.
> It seems wrong to me that an sstable could ever be written to while it's in a
> snapshot.
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