[jira] Commented: (CASSANDRA-226) Make time-sorted CFs behave consistently

["Jun Rao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12720933#action_12720933 ] 

Jun Rao commented on CASSANDRA-226:
-----------------------------------

For time-sorted CFs, within an SSTable, there shouldn't be duplicated columns. Otherwise, older versions of a column never get garbage collected. 

The two separate maps within Memtable are convenient for incrementally maintaining columns in timestamp order as well as doing efficient updates by column names. I am not sure how you can reduce it to one map without sacrificing performance.



> Make time-sorted CFs behave consistently
> ----------------------------------------
>
>                 Key: CASSANDRA-226
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-226
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>
> Time-sorted CFs are indexed and sorted by time in the SSTable.  So lookup by name is inefficient, and compaction sucks, because we combine by name even though we sort by time. (CASSANDRA-16)
> The right fix is, for time-sorted columns we need to recognize that the right "key" as it were is (time, name) not name.  We should allow slice by time and lookup by time or time,name but not just name.  (Similarly, we should not allow lookup by time on name-sorted CFs.)  This means that name will not necessarily be unique in time-sorted CFs but that is the right behavior!  Time-based CFs are more like appending to a list than putting to a map.
> (As part of this we could track the most recent append in time-sorted CFs to prevent the bug in CASSANDRA-223.  I am not sure that is the "right" way to go but I do mention it as a possibility that this change enables.)
> In the code, this will allow more regular treatment of CFs and less special casing.  (It will also allow using only a single map for memtable columns, reducing memory usage -- see CASSANDRA-51.)
> Implementation notes: we may be able to represent both types of CF with a pluggable Comparator + Indexer combination, which would solve CASSANDRA-185 and CASSANDRA-189 at the same time.

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