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From "Aaron Morton (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (CASSANDRA-2589) row deletes do not remove columns
Date Mon, 02 May 2011 04:53:03 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2589?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13027543#comment-13027543
] 

Aaron Morton edited comment on CASSANDRA-2589 at 5/2/11 4:51 AM:
-----------------------------------------------------------------

bq. What's supposed to happen is, isRelevant will supress those columns (which may be in an
older sstable). We should never require a read (e.g. to load a list of all-columns-deleted),
when doing a write.

Was only thinking about the columns in the memtable. edit: I think the best idea is to ignore
the columns when serialising the CF to SSTable. 

bq. If you have columns in memory when you do a row deletion, it shouldn't matter whether
we write those out or not, as far as correctness is concerned.

agree this was more of a performance issue, e.g. write a lot of data and delete it quickly
(before memtable flush) using a row delete takes more disk space than deleting by column path.


CASSANDRA-2590 is where I noticed it breaking correctness.     

      was (Author: amorton):
    bq. What's supposed to happen is, isRelevant will supress those columns (which may be
in an older sstable). We should never require a read (e.g. to load a list of all-columns-deleted),
when doing a write.

Was only thinking about the columns in the memtable. 

bq. If you have columns in memory when you do a row deletion, it shouldn't matter whether
we write those out or not, as far as correctness is concerned.

agree this was more of a performance issue, e.g. write a lot of data and delete it quickly
(before memtable flush) using a row delete takes more disk space than deleting by column path.


CASSANDRA-2590 is where I noticed it breaking correctness.     
  
> 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
>
> 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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