View Snapshot Isolation Disk Usage

Snapshot isolation stores row versions in tempdb, and a runaway snapshot transaction can fill it. This query compares each database's version store space usage against tempdb's total page count - reporting reserved pages and kilobytes, the snapshot's percentage of tempdb, and how full tempdb is overall.

SELECT
	DB_NAME(vssu.database_id) AS DatabaseName,
    SUM(vssu.reserved_page_count),
    SUM(vssu.reserved_space_kb),
    SUM(tdbu.total_page_count) as tempdb_pages,
    SUM((vssu.reserved_page_count * 100.0) / (tdbu.total_page_count + 0.0)) AS [Snapshot %],
    SUM((tdbu.allocated_extent_page_count * 100.0) / (tdbu.total_page_count + 0.0)) AS [tempdb % used]
FROM
	sys.dm_tran_version_store_space_usage as vssu
    CROSS JOIN tempdb.sys.dm_db_file_space_usage as tdbu
GROUP BY
	DB_NAME(vssu.database_id)