[jira] [Commented] (CASSANDRA-4175) Reduce memory (and disk) space requirements with a column name/id map

["Jonathan Ellis (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4175?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13257836#comment-13257836 ] 

Jonathan Ellis commented on CASSANDRA-4175:
-------------------------------------------

The wrinkle here is concurrent schema changes -- how can we make sure each node uses the same column ids for each name?  I see two possible approaches:

# embed something like Zookeeper to standardize the id map
# punt: let each node use a node-local map, and translate back and forth to full column name across node boundaries

                
> Reduce memory (and disk) space requirements with a column name/id map
> ---------------------------------------------------------------------
>
>                 Key: CASSANDRA-4175
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4175
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>             Fix For: 1.2
>
>
> We spend a lot of memory on column names, both transiently (during reads) and more permanently (in the row cache).  Compression mitigates this on disk but not on the heap.
> The overhead is significant for typical small column values, e.g., ints.
> Even though we intern once we get to the memtable, this affects writes too via very high allocation rates in the young generation, hence more GC activity.
> Now that CQL3 provides us some guarantees that column names must be defined before they are inserted, we could create a map of (say) 32-bit int column id, to names, and use that internally right up until we return a resultset to the client.

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