Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Figure 14-1
Data needed
Data in cache? No
Yes
Read or modify
data in cache
Data changed?
Yes
Write changes
to log
Failure and Recovery
Room in cache
for new data?
A recovery happens every time that SQL Server starts. SQL Server takes the database file, then applies (by
writing them out to the physical database file) any committed changes that are in the log since the last
checkpoint. Any changes in the log that do not have a corresponding commit are rolled back — that is,
they are essentially forgotten.
Let’s take a look at how this works depending on how transactions have occurred in your database.
Imagine five transactions that span the log as pictured in Figure 14-2.
Yes
Read data
into cache so
placing least
recently used
data
Let’s look at what would happen to these transactions one by one.
Chapter 14: Transactions and Locks
No
Issue checkpoint
Write any
modified
cache
pages to disk
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