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From "Branimir Lambov (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-9195) commitlog replay only actually replays mutation every other time
Date Thu, 23 Apr 2015 16:08:40 GMT


Branimir Lambov commented on CASSANDRA-9195:

bq. Branimir Lambov confused why you are changing sstable loader and not commit log replay?

Because commitlog is acting correctly, it should not replay truncated data regardless of where
it comes from. In this particular case sstable loader is leaving the table in a bad state;
rather than try to live with it I prefer to correct it at the origin.

bq. If your goal is to restore the data you truncated, then you shouldn't be using PITR restore
for that, you should be putting the sstables from the auto snapshot back in place.

The PITR process _includes_ a truncation step. What I am doing here is giving PITR the option
to correctly continue after that step.

> commitlog replay only actually replays mutation every other time
> ----------------------------------------------------------------
>                 Key: CASSANDRA-9195
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jon Moses
>            Assignee: Branimir Lambov
>            Priority: Critical
>             Fix For: 2.1.5
>         Attachments: 9195-v2.1.patch,
> Version: Cassandra | 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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