Check progress of alter index reorganize / rebuild

It's really hard to say how long your rebuild will take, as SQL itself doesn't really know in advance and cant give you an estimate.

You can use the following query to use the dm_exec_requests dmv to view how long your index rebuild has been going on for, and to verify that SQL doesn't really have an estimate:

SELECT r.session_id,r.command,CONVERT(NUMERIC(6,2),r.percent_complete)
AS [Percent Complete],CONVERT(VARCHAR(20),DATEADD(ms,r.estimated_completion_time,GetDate()),20) AS [ETA Completion Time],
CONVERT(NUMERIC(10,2),r.total_elapsed_time/1000.0/60.0) AS [Elapsed Min],
CONVERT(NUMERIC(10,2),r.estimated_completion_time/1000.0/60.0) AS [ETA Min],
CONVERT(NUMERIC(10,2),r.estimated_completion_time/1000.0/60.0/60.0) AS [ETA Hours],
CONVERT(VARCHAR(1000),(SELECT SUBSTRING(text,r.statement_start_offset/2,
CASE WHEN r.statement_end_offset = -1 THEN 1000 ELSE (r.statement_end_offset-r.statement_start_offset)/2 END)
FROM sys.dm_exec_sql_text(sql_handle)))
FROM sys.dm_exec_requests r WHERE command IN ('Alter Index')

However when it comes to a real estimate on time required you can read this nice blog post from sqlmunkee, which summarises this by saying "..it depends. ":

And since we're not all on the same hardware, using the same software, or looking at the same data, the answer has to be… ..it depends

Frustrating, but true, sadly.

I managed to find this blog post with a magick script which allegedly does the task, can't check because this seems to not work for SQL Server 2014 which I am running, query blocks waiting for a Shared Lock. Maybe someone will find it useful though so I will just leave it here.

;WITH cte AS
(
SELECT
object_id,
index_id,
partition_number,
rows,
ROW_NUMBER() OVER(PARTITION BY object_id, index_id, partition_number ORDER BY partition_id) as rn
FROM sys.partitions
)
SELECT
   object_name(cur.object_id) as TableName,
   cur.index_id,
   cur.partition_number,
   PrecentDone =
      CASE
         WHEN pre.rows = 0 THEN 0
      ELSE
         ((cur.rows * 100.0) / pre.rows)
      END,
   pre.rows - cur.rows as MissingRows
FROM cte as cur
INNER JOIN cte as pre on (cur.object_id = pre.object_id) AND (cur.index_id = pre.index_id) AND (cur.partition_number = pre.partition_number) AND (cur.rn = pre.rn +1)
ORDER BY 4