Database Log File Getting Full 

SQL Server databases are primarily backed by two categories of files – data files and log files. The data files contain all of the data related to the database, including tables, indexes, and object definitions, while the log files contain a log of all of the changes which have been made to that data. This separation of log and data files is critical to ensuring the recoverability of the data in the case of an unexpected server failure.

Under normal circumstances, the space in the log file is regularly reused, with space being made available for reuse through a process called log truncation. When log truncation cannot occur for some reason, the log file will attempt to grow if autogrow is enabled and the file has not reached its maximum size. When a log file becomes full and can no longer grow, attempts to modify or add data to the database will produce an error: the database will essentially become read-only.

When a database log file is full, it is important to identify what is preventing log truncation from occurring. Two common reasons that the log might not be truncating include:

There are other reasons truncation may not occur: full details are available .

If you are not immediately able to resolve the problem that is preventing log truncation, you may need to take another action to create space for the log file. This can include freeing disk space, manually increasing the log file size, or adding an additional log file. Each of those options, along with their implications, is explained , and can be summarized thus:

It’s a good practice to keep an eye on the sizes of your log files and the space remaining and to take action before reaching a critical stage.  You can read more about managing transaction log sizes .

 

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