cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6696) Drive replacement in JBOD can cause data to reappear.
Date Thu, 01 May 2014 18:33:15 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13986845#comment-13986845
] 

Benedict commented on CASSANDRA-6696:
-------------------------------------

Or (somewhat handwavy, just to give a basic outline of the idea): we could say each vnode
has its own LCS hierarchy - this is optimal from a read perspective - and perhaps have L1
switch to 1 file in size by default (L2 being 10, etc), and then for our flush to L0 we write
files equivalent in size to one L1 file, grouping however many vnodes fit in the flush, and
then only merge with the individual L1s once the density of the relevant portion of L0 is
> ~0.5 per vnode

> Drive replacement in JBOD can cause data to reappear. 
> ------------------------------------------------------
>
>                 Key: CASSANDRA-6696
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6696
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: sankalp kohli
>            Assignee: Marcus Eriksson
>             Fix For: 3.0
>
>
> In JBOD, when someone gets a bad drive, the bad drive is replaced with a new empty one
and repair is run. 
> This can cause deleted data to come back in some cases. Also this is true for corrupt
stables in which we delete the corrupt stable and run repair. 
> Here is an example:
> Say we have 3 nodes A,B and C and RF=3 and GC grace=10days. 
> row=sankalp col=sankalp is written 20 days back and successfully went to all three nodes.

> Then a delete/tombstone was written successfully for the same row column 15 days back.

> Since this tombstone is more than gc grace, it got compacted in Nodes A and B since it
got compacted with the actual data. So there is no trace of this row column in node A and
B.
> Now in node C, say the original data is in drive1 and tombstone is in drive2. Compaction
has not yet reclaimed the data and tombstone.  
> Drive2 becomes corrupt and was replaced with new empty drive. 
> Due to the replacement, the tombstone in now gone and row=sankalp col=sankalp has come
back to life. 
> Now after replacing the drive we run repair. This data will be propagated to all nodes.

> Note: This is still a problem even if we run repair every gc grace. 
>  



--
This message was sent by Atlassian JIRA
(v6.2#6252)

Mime
View raw message