SQLite is a light weight relational database management system that facilitates for quick processing of the data stored within it. Data processing in SQLite is carried out by in –process library which works on an absolutely zero configuration SQL database engine involving no server connections. The predominant database files of SQLite which is also known as SQLite database is a framework that consists of elements like tables, triggers, views, schemas and indices. SQLite saves all its user and Meta data related to the database in a single big file. The file name is also same as the database name.
SQLite database helps in storing large chunks of data in a number of tables. However, the data stored across these tables do not help in event reconstruction. SQLite database consists of three types of journal files and WAL files that can help users in the process of event reconstruction. Let us get a deep delve into the journal files of SQLite. As the explanation given about the files is theoretical for getting the practical knowledge or to visualize these files you can also use a free utility “SQLite db Browser”. So know we will move to understand the technological aspects of WAL and journal SQLite files.
Get an Insight into WAL and Journal Files of SQLite
Rollback Journal: SQLite maintains a rollback journal file for each and every database .This journaling related data is stored in the main memory of the SQLite database. It is one of the traditional procedure employed by SQLite to perform atomic commit and rollback of transaction.
SQLite creates journal file for every transaction and then deletes them when the transaction gets complete.
Note: It can be easily figured out because it is present in the same directory as the main database file. Further, its name is exactly similar to the main database file except the name journal appended at the end of the file.
Structure of Rollback Journal File
Each rollback journal is divided into log segments that vary in size. A log segment begins with a header record succeeded by one or more log records that are discussed in details below.
Whenever there is a crash, the data stored in the rollback journal is written to the database file in order to resume the database operations and restore the database to the state where it let off. On deleting the rollback journal, commit occurs to notify the end of a transaction.
For enhancing the speed and concurrency of transactions that take place with SQLite database, a new backup procedure is employed that makes use of WAL files.
Write Ahead Log Files
In case of Write Ahead Log files, no changes are incorporated in the original database file rather the alterations are made to another WAL file. After the record is appended to the WAL files, a special record manifesting the atomic commit indicates the end of database transaction. The movement of pages from the WAL file back to the original database is known as checkpoint.
Why WAL Files are generally favored by Users?
Reading and writing on database occur at the same time as the readers do not block the writers and vice-versa
Disk specific input and output processes get more sequential when using WAL [[PASTING TABLES IS NOT SUPPORTED]]
Note: When the WAL files reach at a size of 1000 pages, a checkpoint automatically occurs. Forensically, one can get to view the WAL files when a SQLite database is opened. Here, if a WAL file is present then the content of the WAL file will be written to the main databases.
Conclusion
The above content fairly describes the way in which SQLite operates at the time that when a specific document is written or last updated. Nevertheless, there is no guarantee if the updated versions of SQLite will make use of the temporary files in the same manner.Some times situation occurs when these sQLite files get corrupted due to some reason so for that situation SQLite Recovery Tool can be helpful. To know more about WAL and journal files and how to perform their forensics please visit:
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