# Sqlite Reader Writer Concurrency (RWC)
This crate presents an opinionated approach on how to interact with a sqlite
database to maximize the reader writer concurrency.
## Setup
Sqlite only supports on write operation at any given time. However, in WAL mode
multiple readers can operate on the database without blocking the writer and
vice versa.
To leverage this, the [`ConnectionPool`] maintains a list of read only connections
and one write connection. This allows multiple readers to access the database and
we enforce exclusive access to the writer connection.
While Sqlite does have internal mechanisms to enforce exclusive write access, they
are a bit limited and mostly rely on an sleep-retry loop. By enforcing exclusive
access to the writer at this level, we can have more predictable writer access
behaviors and we only have to deal with `SQLITE_BUSY` errors from another process.
Finally, since all other connections are read only, we also ensure that it is not
possible to accidentally write something outside of the designated writer.
## Async
This crate also contains a basic async wrapper for the [`ConnectionPool`], where
each connection is assigned its own thread and communication occurs over a channel.
This can be enabled with the `async` feature.
## Example
```rust
use sqlite_rwc::{SyncConnectionPool, ConnectionPoolConfig};
use sqlite_rwc::drivers::rusqlite::RusqliteDriver;
use tempdir::TempDir;
let temp_dir = TempDir::new("sqlite-wrc-example").unwrap();
let db_path = temp_dir.path().join("sqlite.db");
let config = ConnectionPoolConfig {
max_read_connection_count: 4,
file_path: db_path,
connection_acquire_timeout: None,
#[cfg(feature="watcher")]
watcher: sqlite_watcher::watcher::Watcher::new().unwrap(),
};
let pool = SyncConnectionPool::<RusqliteDriver>::new(config).unwrap();
let mut connection = pool.connection().unwrap();
//unscoped read operation ...
connection.execute_batch("SQL");
Ok(())
}).unwrap();
connection.transaction_closure(|conn| -> rusqlite::Result<()>{
//transaction operation
Ok(())
}).unwrap();
```