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From "Aaron Morton (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-2589) row deletes do not remove columns
Date Mon, 16 May 2011 01:07:47 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-2589?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Aaron Morton updated CASSANDRA-2589:
------------------------------------

    Attachment: 0001-remove-deleted-columns-before-flushing-memtable-v07.patch
                0001-remove-deleted-columns-before-flushing-memtable-v08.patch

Patch to remove deleted columns inside of Memtable.writeSortedContents() 

- did not just skip them in ColumnFamilySerialiser.serialiseForSSTable as  that is also used
for inter node messages. 
- not in CFS.serializeWithIndexes() because it would have to remove them from the CF before
building the column index and that felt bad. 
- writes an empty CF if it has been marked for delete because the system tables have GCGraceSeconds
0 and it can lose the delete.  

> row deletes do not remove columns
> ---------------------------------
>
>                 Key: CASSANDRA-2589
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2589
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.7.5, 0.8 beta 1
>            Reporter: Aaron Morton
>            Assignee: Aaron Morton
>            Priority: Minor
>         Attachments: 0001-remove-deleted-columns-before-flushing-memtable-v07.patch,
0001-remove-deleted-columns-before-flushing-memtable-v08.patch
>
>
> When a row delete is issued CF.delete() sets the localDeletetionTime and markedForDeleteAt
values but does not remove columns which have a lower time stamp. As a result:
> # Memory which could be freed is held on to (prob not too bad as it's already counted)
> # The deleted columns are serialised to disk, along with the CF info to say they are
no longer valid. 
> # NamesQueryFilter and SliceQueryFilter have to do more work as they filter out the irrelevant
columns using QueryFilter.isRelevant()
> # Also columns written with a lower time stamp after the deletion are added to the CF
without checking markedForDeletionAt.
> This can cause RR to fail, will create another ticket for that and link. This ticket
is for a fix to removing the columns. 
> Two options I could think of:
> # Check for deletion when serialising to SSTable and ignore columns if the have a lower
timestamp. Otherwise leave as is so dead columns stay in memory. 
> # Ensure at all times if the CF is deleted all columns it contains have a higher timestamp.

> ## I *think* this would include all column types (DeletedColumn as well) as the CF deletion
has the same effect. But not sure.
> ## Deleting (potentially) all columns in delete() will take time. Could track the highest
timestamp in the CF so the normal case of deleting all cols does not need to iterate. 
>  

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