James Taylor created PHOENIX-2143:
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Summary: Use region start key 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
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|
|GUIDE_POST_WIDTH|LONG|
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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