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From "Sergio Bossa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7870) Cannot execute logged batch when only the coordinator node is alive
Date Wed, 03 Sep 2014 18:40:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14120233#comment-14120233
] 

Sergio Bossa commented on CASSANDRA-7870:
-----------------------------------------

bq. batchlog is concerned with permadeath and not just temporary outages

Right, but the "single node alive" case is still a valid degenerate case. 
If we allow logged batches in such case, we have the following failure scenarios:
1) Permanent death of the coordinator node mid-batch: no one else has seen the partial batch
application, so any node coming back alive after it will not suffer any inconsistencies.
2) Temporary death with restart: the node will replay the batch (with outdated mutations being
discarded).

There may be implementation details I'm missing or oversimplifying (and I'd argue replaying
on restart at a later unknown point in time sounds a bit dangerous so I wouldn't actually
do it and make this degenerate case fall in the same category as "I want ANY consistency"),
but in terms of "contract", I don't see how it is violated at all.

> Cannot execute logged batch when only the coordinator node is alive
> -------------------------------------------------------------------
>
>                 Key: CASSANDRA-7870
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7870
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Sergio Bossa
>            Priority: Critical
>
> As per issue summary.
> This is probably a bug, rather than a consequence of needing to replicate the batchlog,
as if only the coordinator is alive the batch cannot be partially executed on other nodes
(as there are no other nodes).



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