Change index on mod_shredder.shredded_job to improve performance

[eiffel777]

The xdmod-slurm-helper script runs the following query to try and find the time of the most recent job ingested in order to set the start time for the sacct command. Changing the order of the columns for the end_time index on mod_shredder.shredded provides a performance improvement. On metrics-dev, the query went from 6-8 minutes for the ub-hpc resource to around 30 seconds.

SELECT
  DATE_FORMAT(
    FROM_UNIXTIME(MAX(end_time)),
    '%Y-%m-%d %H:%i:%s'
   ) AS max_datetime
FROM shredded_job
WHERE resource_name = :resource

Tests performed

Tested in docker and on metrics-dev

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