It is always safe, and by "safe" I mean "safe for data". You won't have to deal with data corruption. Precisely, see "How To Corrupt An SQLite Database File":
https://www.sqlite.org/howtocorrupt.htmlNow concurrent accesses from different processes/connections can lead to runtime errors (SQLITE_BUSY), because the database happens to be locked by one connection.
Those errors are greatly reduced by the WAL mode (https://sqlite.org/wal.html) which provides ultra-robust single-writer/multiple-readers semantics:
- Writes can not happen concurrently (SQLITE_BUSY).
- One can reduce the occurrences of such SQLITE_BUSY errors by using a built-in timeout (https://www.sqlite.org/c3ref/busy_timeout.html).
- Several reads can happen concurrently, including with writers.
- A writer connection can enter the "Serializable" isolation level.
- A reader connection can enter the "Snapshot Isolation" level.
For more details, see https://www.sqlite.org/isolation.html
During all the years I've been developing the GRDB library (https://github.com/groue/GRDB.swift), I could never see SQLite fail its documented guarantees. This made it possible to build one of the most concurrency-focused SQLite toolkit for Swift, and I'm pretty happy with it (https://github.com/groue/GRDB.swift/blob/master/Documentatio...).
Now concurrent accesses from different processes/connections can lead to runtime errors (SQLITE_BUSY), because the database happens to be locked by one connection.
Those errors are greatly reduced by the WAL mode (https://sqlite.org/wal.html) which provides ultra-robust single-writer/multiple-readers semantics:
- Writes can not happen concurrently (SQLITE_BUSY).
- One can reduce the occurrences of such SQLITE_BUSY errors by using a built-in timeout (https://www.sqlite.org/c3ref/busy_timeout.html).
- Several reads can happen concurrently, including with writers.
- A writer connection can enter the "Serializable" isolation level.
- A reader connection can enter the "Snapshot Isolation" level.
For more details, see https://www.sqlite.org/isolation.html
During all the years I've been developing the GRDB library (https://github.com/groue/GRDB.swift), I could never see SQLite fail its documented guarantees. This made it possible to build one of the most concurrency-focused SQLite toolkit for Swift, and I'm pretty happy with it (https://github.com/groue/GRDB.swift/blob/master/Documentatio...).