Overview: Databases

Server databases organize persistent records through transaction, logging and locking mechanisms.

A catalogue record has to remain coherent as readers and writers perform work. Transactions supply completion boundaries, WAL changes where committed state can be represented, and locking coordinates conflicting operations. These pages connect the library's stored information to those mechanisms and their recovery implications.

• Library databases
  A library database organizes indexed media records and relationships for queries, while source files and user-specific state retain separate roles.

• Database transactions
  A database transaction groups related changes under atomicity and isolation rules, while commit durability and external effects require their own guarantees.

• Database write-ahead logging
  Write-ahead logging records committed database changes in a log before checkpointing them into the main file, supporting reader snapshots with particular concurrency rules.

• Database locking
  Database locking coordinates conflicting operations, and a busy result can require waiting, ending a snapshot or restarting a transaction according to its cause.

References

• SQLite database-file format
• SQLite transaction control
• SQLite write-ahead logging
• SQLite isolation and concurrency