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Comments on: Which LOB pages are associated with a specific columnstore segment? https://www.sqlskills.com/blogs/joe/which-lob-pages-are-associated-with-a-segment/ SQL Server Performance Tuning, High Availability and Disaster Recovery Blog Fri, 02 Aug 2013 22:32:52 +0000 hourly 1 https://wordpress.org/?v=6.9.4 By: Joseph Sack https://www.sqlskills.com/blogs/joe/which-lob-pages-are-associated-with-a-segment/#comment-2765 Fri, 02 Aug 2013 22:32:52 +0000 http://3.209.169.194/blogs/joe/?p=954#comment-2765 In reply to Jayashree.

Hi Jayashree,

A few questions:

Is there concurrent activity on this SQL Server instance or is this an isolated environment?

Is the variation easily reproducible? And if so – can you share your test framework and I can look at it firsthand?

Cheers,

Joe

]]> By: Jayashree https://www.sqlskills.com/blogs/joe/which-lob-pages-are-associated-with-a-segment/#comment-2741 Thu, 25 Jul 2013 18:00:57 +0000 http://3.209.169.194/blogs/joe/?p=954#comment-2741 Hi Joe,

I created an XE Session for the physical read event using SSMS and monitored the physical page reads for a table in which there is a columnstore index. This table has a LOB_Used_Page_Count of 1018. There are no other large objects other than ColumnStore Index data.

After cleaning the buffers, When I ran a query which selects all the columns in the columnstore index, and watch the live data, the physical read events vary anywhere between 788 to 1148. I filtered to made sure that no other session’s data is coming in and could clearly see that these events are created due to the execution of the query using columnstore index.

Can you please explain why are the physical reads varying each time I execute the query after cleaning the buffers, if the same data residing in each page is read. Am I missing something?

Thanks,
Jayashree

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