What is a lob logical read?

What is a lob logical read?

The reasons you see multiple LOB logical reads per row is a because when stored off-row, LOBs are stored in a BTree. So the pointer on the data page points to the root of a BTree, which contains the page pointers for the actual data. So there’s at least 2 Logical IOs required to actually get the LOB data.

How do I reduce logical reads in Sybase?

Usually the best way to reduce logical read is to apply correct index or to rewrite the query. Physical read indicates total number of data pages that are read from disk. In case no data in data cache, the physical read will be equal to number of logical read. And usually it happens for first query request.

What is the use of statistics io in SQL Server?

STATISTICS IO provides detailed information about the impact that your query has on SQL Server. It tells you the number of logical reads (including LOB), physical reads (including read-ahead and LOB), and how many times a table was scanned.

What is the difference between physical read and logical read in SQL Server?

If the page is not currently in the buffer cache, a physical read first copies the page from disk into the cache. So, a logical read is when the query engine needs to read data. First, it looks in memory. If the page is already in SQL Server’s memory, then it uses that.

What is lob in SQL Server?

Dealing with large object (LOB) data is one of the challenges of managing SQL Server installations. LOBs are usually composed of pictures but they can contain other data as well. Typically these images are used to display product images or other graphical media on a website, and they can be quite large.

What is scan count in SQL Server?

Scan count simply means how many times the table or index was accessed during the query. It may be a full scan, partial scan, or simply a seek.

What is physical read and logical read?

What is the difference between physical and logical read?

logical reads – Number of pages read from the data cache. physical reads – Number of pages read from disk.

How does statistics Io work in SQL Server?

STATISTICS IO provides detailed information about the impact that your query has on SQL Server. It tells you the number of logical reads (including LOB), physical reads (including read-ahead and LOB), and how many times a table was scanned.

Can you rely on statistics Io to tell you the truth?

In short, be very aware that there are some scenarios where you can’t rely on STATISTICS IO to tell you the truth. In some cases (this one involving TOP and parallelism), it will vastly under-report logical reads. This can lead you to believe you have a very I/O-friendly query when you don’t.

Do you need showplan permission for set statistics Io?

To use SET STATISTICS IO, users must have the appropriate permissions to execute the Transact-SQL statement. The SHOWPLAN permission isn’t required. This example shows how many logical and physical reads are used by SQL Server as it processes the statements. Table ‘ProductCostHistory’.

How many logical reads are in a scan?

Scan count 1, logical reads 110, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. So it seems that we can easily reproduce this at will with a TOP operator and a low enough DOP.