[jira] [Updated] (CASSANDRA-12991) Inter-node race condition in validation compaction

["Benjamin Roth (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-12991?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Benjamin Roth updated CASSANDRA-12991:
--------------------------------------
    Description: 
Problem:
When a validation compaction is triggered by a repair it may happen that due to flying in mutations the merkle trees differ but the data is consistent however.

Example:
t = 10000: 
Repair starts validation
Node A starts validation
t = 10001:
Mutation arrives at Node A
t = 10002:
Mutation arrives at Node B
t = 10003:
Node B starts validation

Hashes of node A+B will differ but data is consistent from a view (think of it like a snapshot) t = 10000.

Impact:
Unnecessary streaming happens. This may not a big impact on low traffic CFs, partitions but on high traffic CFs and maybe very big partitions, this may have a bigger impact and is a waste of resources.

Possible solution:
Build hashes based upon a snapshot timestamp.
This requires SSTables created after that timestamp to be filtered when doing a validation compaction:
- Cells with timestamp > snapshot time have to be removed
- Tombstone range markers have to be handled
 - Bounds have to be removed if delete timestamp > snapshot time
 - Boundary markers have to be either changed to a bound or completely removed, depending if start and/or end are both affected or not

Probably this is a known behaviour. Have there been any discussions about this in the past? Did not find an matching issue, so I created this one.

I am happy about any feedback, whatsoever.

  was:
Problem:
When a validation compaction is triggered by a repair it may happen that due to flying in mutations the merkle trees differ but the data is not consistent.

Example:
t = 10000: 
Repair starts validation
Node A starts validation
t = 10001:
Mutation arrives at Node A
t = 10002:
Mutation arrives at Node B
t = 10003:
Node B starts validation

Hashes of node A+B will differ but data is consistent from a view (think of it like a snapshot) t = 10000.

Impact:
Unnecessary streaming happens. This may not a big impact on low traffic CFs, partitions but on high traffic CFs and maybe very big partitions, this may have a bigger impact and is a waste of resources.

Possible solution:
Build hashes based upon a snapshot timestamp.
This requires SSTables created after that timestamp to be filtered when doing a validation compaction:
- Cells with timestamp > snapshot time have to be removed
- Tombstone range markers have to be handled
 - Bounds have to be removed if delete timestamp > snapshot time
 - Boundary markers have to be either changed to a bound or completely removed, depending if start and/or end are both affected or not

Probably this is a known behaviour. Have there been any discussions about this in the past? Did not find an matching issue, so I created this one.

I am happy about any feedback, whatsoever.


> Inter-node race condition in validation compaction
> --------------------------------------------------
>
>                 Key: CASSANDRA-12991
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12991
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benjamin Roth
>            Priority: Minor
>
> Problem:
> When a validation compaction is triggered by a repair it may happen that due to flying in mutations the merkle trees differ but the data is consistent however.
> Example:
> t = 10000: 
> Repair starts validation
> Node A starts validation
> t = 10001:
> Mutation arrives at Node A
> t = 10002:
> Mutation arrives at Node B
> t = 10003:
> Node B starts validation
> Hashes of node A+B will differ but data is consistent from a view (think of it like a snapshot) t = 10000.
> Impact:
> Unnecessary streaming happens. This may not a big impact on low traffic CFs, partitions but on high traffic CFs and maybe very big partitions, this may have a bigger impact and is a waste of resources.
> Possible solution:
> Build hashes based upon a snapshot timestamp.
> This requires SSTables created after that timestamp to be filtered when doing a validation compaction:
> - Cells with timestamp > snapshot time have to be removed
> - Tombstone range markers have to be handled
>  - Bounds have to be removed if delete timestamp > snapshot time
>  - Boundary markers have to be either changed to a bound or completely removed, depending if start and/or end are both affected or not
> Probably this is a known behaviour. Have there been any discussions about this in the past? Did not find an matching issue, so I created this one.
> I am happy about any feedback, whatsoever.



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