Determing the position of the last VLF in transaction log before shrinking the log file

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Returns Virtual log file (VLF)  information of the transaction log. Note all transaction log files are combined in the table output. Each row in the output represents a VLF in the transaction log and provides information relevant to that VLF in the log.

sys.dm_db_log_info ( database_id )


The following query can be used to determine the position of the last active VLF before running shrinkfile on transaction log to determine if transaction log can shrink.


USE AdventureWorks2016

;WITH cte_vlf AS (
SELECT ROW_NUMBER() OVER(ORDER BY vlf_begin_offset) AS vlfid, DB_NAME(database_id) AS [Database Name], vlf_sequence_number, vlf_active, vlf_begin_offset, vlf_size_mb
  FROM sys.dm_db_log_info(DEFAULT)),
cte_vlf_cnt AS (SELECT [Database Name], COUNT(vlf_sequence_number) AS vlf_count,
  (SELECT COUNT(vlf_sequence_number) FROM cte_vlf WHERE vlf_active = 0) AS vlf_count_inactive,
  (SELECT COUNT(vlf_sequence_number) FROM cte_vlf WHERE vlf_active = 1) AS vlf_count_active,
  (SELECT MIN(vlfid) FROM cte_vlf WHERE vlf_active = 1) AS ordinal_min_vlf_active,
  (SELECT MIN(vlf_sequence_number) FROM cte_vlf WHERE vlf_active = 1) AS min_vlf_active,
  (SELECT MAX(vlfid) FROM cte_vlf WHERE vlf_active = 1) AS ordinal_max_vlf_active,
  (SELECT MAX(vlf_sequence_number) FROM cte_vlf WHERE vlf_active = 1) AS max_vlf_active
  FROM cte_vlf
  GROUP BY [Database Name])
SELECT [Database Name], vlf_count, min_vlf_active, ordinal_min_vlf_active, max_vlf_active, ordinal_max_vlf_active,
((ordinal_min_vlf_active-1)*100.00/vlf_count) AS free_log_pct_before_active_log,
((ordinal_max_vlf_active-(ordinal_min_vlf_active-1))*100.00/vlf_count) AS active_log_pct,
((vlf_count-ordinal_max_vlf_active)*100.00/vlf_count) AS free_log_pct_after_active_log
FROM cte_vlf_cnt


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