What is transaction log?

In database, transaction log is also called database log or binary log, and it's a record of actions. It can record any action by the database and store the recording results in a separate file. The location of the SQL Server transaction log is configured at the same time as the database is created. When creating a database, the location of the SQL Server transaction log is specified as well as other options associated with the transaction log.

If, after a start, the database is in the recode state, transaction logs have not shut down recoding are including all the actions in record range until the users clicking submit or quit. Additionally, all transactions that are already committed but whose changes are not yet materialized in the database are re-applied. Both are done to ensure atomicity and durability of transactions. Each database has at least one transaction log and a data file.

For security in performance, SQL Server stores modifies in cache directory. These modifies will be recorded in transaction logs, but cannot be recorded in data file. Transaction logs will determine a transaction whether it has written the cache files into data file with a marking point. When restart SQL Server, it will check the latest marking pointer in transaction logs, and delete the transaction logs, which are behind this marking pointer, because these transaction logs did not have written the cache files into data files. This can prevent the disruption transaction from modifying data files.

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