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From "James Taylor (JIRA)" <>
Subject [jira] [Commented] (PHOENIX-2143) Use guidepost bytes instead of region name in stats primary key
Date Wed, 23 Dec 2015 02:07:46 GMT


James Taylor commented on PHOENIX-2143:

Thanks for the WIP patch, [~ankit.singhal]. The row key structure looks correct, but I don't
think you'll need to change GuidePostsInfo to List<GuidePostsInfo> as GuidePostsInfo
encapsulates all the guideposts across a table per column family. This object is sent across
the wire as part of the PTable (the metadata for a table) and we'll want to continue doing
that (the client caches the guideposts across the entire table). I don't think this change
will impact the client-side much (other than perhaps a few minor tweaks).

The primary changes on the server side will be:
- Removing any stats-related logic when a split occurs. Nothing will be required during a
- We previously could delete the row that stored *all* guideposts for a given table/region/cf,
but this will no longer be possible. Instead, when we update the stats for a region, we'll
run a query to collect up all the guideposts that'll be deleted by querying the stats table
for all guideposts between the start region and end region key:
    SELECT guide_post_key FROM SYSTEM.STATS
    WHERE physical_name = ? and family_name = ? and guide_post_key >= :1 AND guide_post_key
< :2
with the :1 is bound to the start region key and :2 is bound to the end region key (with some
variation on the first and last region that are unbound at the beginning/end of the range).
Based on this query, we can form the row keys of the guideposts we need to delete and add
these mutations to the list of mutations we submit with the puts for the new guideposts.

> Use guidepost bytes instead of region name in stats primary key
> ---------------------------------------------------------------
>                 Key: PHOENIX-2143
>                 URL:
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Ankit Singhal
>         Attachments: PHOENIX-2143_wip.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 <
> {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.
> 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.

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