What is the purpose of the transaction log?

The transaction log records every change that occurs within a database to persist all transactions to disk.

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What are the types of files that you create for databases and what are the commonly used

You can create data and log files for a database. Data files commonly have either an .mdf or .ndf extension, whereas log files have an .ldf extension

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What is Check pointing in SQL Server ?

If you are adding new data to a database, the new data is first written to a memory buffer, then written to the transaction log, and finally persisted to a data file via a background process called check pointing.

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