[jira] [Commented] (PHOENIX-2143) Use guidepost bytes instead of region name in stats primary key

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-2143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15086706#comment-15086706 ] 

James Taylor commented on PHOENIX-2143:
---------------------------------------

This looks very good, [~ankit.singhal]. For upgrade, I think it's ok to truncate the system.stats table through the hbase admin and document that folks should run UPDATE STATISTICS after they upgrade if they're relying on stats.

For (2), that's an interesting edge case, but IMHO we should just document it as stats are just approximations. If your guidePostSize is greater than your region size, then you've essentially disabled stats so you shouldn't expect to row counts. Did I understand your question correctly?

Is there anything left to do for the patch? Do the tests pass?

[~samarthjain] - would you mind giving this patch a review as well?

 

> Use guidepost bytes instead of region name in stats primary key
> ---------------------------------------------------------------
>
>                 Key: PHOENIX-2143
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2143
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Ankit Singhal
>         Attachments: PHOENIX-2143_wip.patch, PHOENIX-2143_wip_2.patch
>
>
> Our current SYSTEM.STATS table uses the region name as the last column in the primary key constraint. Instead, we should use the MIN_KEY column (which corresponds to the region start key). The advantage would be that the stats would then be ordered by region start key allowing us to approximate the number of guideposts which would be traversed given the start/stop row of a scan:
> {code}
> SELECT SUM(guide_posts_count) FROM SYSTEM.STATS WHERE min_key > :1 AND min_key < :2
> {code}
> where :1 is the start row and :2 is the stop row of the scan. With an UNNEST operator for ARRAYs, we could get a better approximation.
> As part of the upgrade to the new Phoenix version containing this fix, stats could simply be dropped and they'd be recalculated with the new schema.
> An alternative, even more granular approach would be to *not* use arrays to store the guide posts, but instead store them as individual rows with a schema like this.
> |PHYSICAL_NAME|VARCHAR|
> |COLUMN_FAMILY|VARCHAR|
> |GUIDE_POST_KEY|VARBINARY|
> In this alternative, the maintenance during compaction is higher, though, as you'd need to run a separate query to do the deletion of the old guideposts, followed by a commit of the new guideposts. The other disadvantage (besides requiring multiple queries) is that this couldn't be done transactionally.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)