How LSNs Get Generated

Stuart Moore looks at how SQL Server builds log sequence numbers:

If you’ve ever dug down in the SQL Server transaction logs or had to build up restore chains, then you’ll have come across Log Sequence Numbers (LSNs). Ever wondered why they’re so large, why they all look suspiciously the same, why don’t they start from 0 and just how does SQL Server generate these LSNs? Well, here we’re going to take a look at them

Below we’ll go through examples of how to look inside the current transaction log, and backed up transaction logs. This will involve using some DBCC commands and the undocumented fn_dblog and fn_dump_dblog function. The last 2 are very handy for digging into SQL Server internals, but be wary about running them on a production system without understanding what’s going on. They can leave filehandles and processes behind that can impact on your system.

It’s an interesting look into SQL Server’s internals.

Related Posts

Diving Into Clustered Index Seeks

Hugo Kornelis looks in detail at the clustered index seek: The Clustered Index Seek operator uses the structure of a clustered index to efficiently find either single rows (singleton seek) or specific subsets of rows (range seek). Because a clustered index always contains all columns in a table, a Clustered Index Seek is one of the most […]

Read More

Deep Dive on Index Seeks

Hugo Kornelis gives us a great deal of information on index seeks in SQL Server: Every Seek Keys specification can be either for a “singleton seek”, or for a “range seek”. A singleton seek applies when at most a single row can satisfy the requirement of the Seek Keys specification. A range seek means that (potentially) more than a […]

Read More

Categories

March 2018
MTWTFSS
« Feb Apr »
 1234
567891011
12131415161718
19202122232425
262728293031