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Object replication and kafka offset

Hello Support Team!
New version of kafka scheduler in Vertica 10 uses epoch for sorting records in stream_microbatch_history

SELECT * FROM (SELECT *, extract(milliseconds from last_batch_duration::interval second) as ld FROM "KAFKA".stream_microbatch_history LIMIT 1 OVER (PARTITION BY microbatch_id, target_schema, target_table, source_name, source_cluster, source_partition ORDER BY epoch DESC)) as lastframe ORDER BY microbatch_id, target_schema, target_table, source_name, source_cluster, source_partition

But if this table is replicated from another DB all records has the same epoch.

select epoch,count(*) FROM KAFKA.stream_microbatch_history group by 1 order by 1;
 epoch |  count
-------+---------
 48421 | 7552259

And then kafka scheduler estimates incorrect (almost random) last offset from stream_microbatch_history

Is there are any workaround besides of manually updating last records in stream_microbatch_history after replication to change epoch?

        UPDATE KAFKA.stream_microbatch_history
           SET batch_start = batch_start
             , end_offset  = end_offset
         WHERE (
                      microbatch_id, target_schema, target_table, source_name, source_cluster, source_partition, batch_start, start_offset, end_offset
               ) IN (
               SELECT microbatch_id, target_schema, target_table, source_name, source_cluster, source_partition, batch_start, start_offset, end_offset
                 FROM KAFKA.stream_microbatch_history LIMIT 1
                 OVER ( PARTITION BY
                      microbatch_id, target_schema, target_table, source_name, source_cluster, source_partition
                        ORDER BY batch_start DESC
                      )
               )

Used version: Vertica Analytic Database v10.1.0-0

Answers

  • SergeBSergeB Employee

    Hello could you open a support ticket for this issue so that we can properly track the issue? Your workaround seem fine if you have only one epoch in the replicated table.
    Could you explain your scenario (here or in a support ticket)? Are you replicating the microbatch_history table with the intent of running another scheduler from the replicated DB and stopping the scheduler on the source DB? In that case, it might be simpler to only copy the last records in microbatch_history rather than the full table?

  • Hello could you open a support ticket for this issue so that we can properly track the issue?

    No, I'am using the community edition.

    Are you replicating the microbatch_history table with the intent of running another scheduler from the replicated DB and stopping the scheduler on the source DB?

    I use replication in two scenarios:
    1. Recreating short (without some big tables) rel stage db from production for testing
    2. Replicating short recovery db for quick switch with current production db in case of disaster

    In that case, it might be simpler to only copy the last records in microbatch_history rather than the full table?

    It's almost the same workaround.

    So this is an intentional choice (sort by epoch) and you are not planning to change it?

    What about sorting by batch_start / batch_end ?

  • SergeBSergeB Employee

    Sorting by batch_start/batch_end was the previous method. This was changed in recent versions in order to resolve other issues. I will open an internal ticket about the scenario where microbatch_history is replicated. In the meantime, you'll have to use your workaround right before starting your replicated scheduler.

  • I think it's better to sort by epoch + batch_start if there are no more pitfalls )

  • SergeBSergeB Employee

    Thanks for reporting the issue when table is replicated. This will be addressed in upcoming version(s).

  • And what about backups? Are the rows epochs saved in the backup?

  • SergeBSergeB Employee

    The fix will address all circumstances where there isn't one epoch per microbatch run.

  • Thanks! Glad to hear )

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