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As per the title - modified_extent_page_count shows 0 extents modified on a 1.7TB database, but running a differential takes takes 4-5 hours and generates a 50GB file.

I wondered if anyone has come across a similar issue?

This flag was introducted in SQL 2017 and backported to SQL 2016 SP2. The server I am using is SQL 2016 SP2 CU17.

A full backup was created, reducing modified extents to 0. I would have assumed a differential straight after would complete quickly?

Query being run to check extents:

SELECT  DB_NAME() AS [database],
        SUM(allocated_extent_page_count) AS allocated_extent_page_count,
        SUM(modified_extent_page_count) AS modified_extent_page_count,
        CONVERT(DECIMAL(4,2),(SUM(modified_extent_page_count) * 100) / (SUM(allocated_extent_page_count) * 1.)) AS percent_changed
FROM sys.dm_db_file_space_usage

Edit:

I've tested updating a handful of rows and modified extents did not increase - I wonder if extents had been modified in the background but not showing - possible bug. I will have a look to see if I can find one.

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  • Please format your sql by placing 3 backticks on teh line before the sql statement and teh line after it. Feb 2 at 12:04

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