What is transaction log file and its purpose?


The primary function of the transaction log file is to:
 
 
  • Record all changes to the database
  • Record changes sequentially
  • All data is written to the transaction log file first before committing the changes to the data file
  • A triggering mechanism, called a checkpoint,  is triggered each few minutes to the transaction log to indicate that a particular transaction has been completely written from the buffer to the data file;  this process keeps flushes out the committed transaction, and maintains the size of the physical transaction log file (only in simple recovery mode)
  •  Key object needed to restore databases
  • Controls the size of the transaction log file and prevents the log consuming the disk space
  •  Used in log shipping, database mirroring, and replication
  • Allows recover to a point in time

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