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https://issues.apache.org/jira/browse/CASSANDRA-9195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14506733#comment-14506733
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Branimir Lambov commented on CASSANDRA-9195:
--------------------------------------------
The reason for this happening is that a truncation record with the latest
replay position in the existing SSTables is written to the system keyspace, and
the following commit log restore skips over data that has been truncated. In
the next run less data exists, hence the truncation position is earlier than
the replayed commit log, and the stored mutations do get applied.
The commit log behaviour is correct, it should not be restoring truncated data.
Thus I'm not sure if the restore cycle in its current form is correct. It
should be resetting the truncation data as well.
It may be possible to make this part of the sstableload process, but before I
do that I need to look closer at the process to see if it won't cause more
serious problems.
> commitlog replay only actually replays mutation every other time
> ----------------------------------------------------------------
>
> Key: CASSANDRA-9195
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9195
> Project: Cassandra
> Issue Type: Bug
> Reporter: Jon Moses
> Assignee: Branimir Lambov
> Priority: Critical
> Fix For: 2.1.5
>
> Attachments: loader.py
>
>
> Version: Cassandra 2.1.4.374 | DSE 4.7.0
> The main issue here is that the restore-cycle only replays the mutations
> every other try. On the first try, it will restore the snapshot as expected
> and the cassandra system load will show that it's reading the mutations, but
> they do not actually get replayed, and at the end you're left with only the
> snapshot data (2k records).
> If you re-run the restore-cycle again, the commitlogs are replayed as
> expected,
> and the data expected is present in the table (4k records, with a spot check
> of
> record 4500, as it's in the commitlog but not the snapshot).
> Then if you run the cycle again, it will fail. Then again, and it will work.
> The work/
> not work pattern continues. Even re-running the commitlog replay a 2nd time,
> without
> reloading the snapshot doesn't work
> The load process is:
> * Modify commitlog segment to 1mb
> * Archive to directory
> * create keyspace/table
> * insert base data
> * initial snapshot
> * write more data
> * capture timestamp
> * write more data
> * final snapshot
> * copy commitlogs to 2nd location
> * modify cassandra-env to replay only specified keyspace
> * modify commitlog properties to restore from 2nd location, with noted
> timestamp
> The restore cycle is:
> * truncate table
> * sstableload snapshot
> * flush
> * output data status
> * restart to replay commitlogs
> * output data status
> ====
> See attached .py for a mostly automated reproduction scenario. It expects
> DSE (and I found it with DSE 4.7.0-1), rather than "actual" Cassandra, but
> it's not using any DSE specific features. The script looks for the configs
> in the DSE locations, but they're set at the top, and there's only 2 places
> where dse is restarted.
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