Struct ReadTxn 

pub struct ReadTxn<'db, F: FileBackend> { /* private fields */ }

A read transaction.

Construct via ReadTxn::begin. Holds:

1. A ReaderSnapshot pinning the WAL end-LSN at construction.
2. An optional cross-process READER_LOCK byte (shared with other readers but not exclusive with writers — see docs/format.md § File locking).

Reads inside a ReadTxn see a consistent snapshot of the database; pending writes from a concurrent WriteTxn and frames committed AFTER ReadTxn::begin are invisible.

Implementations

impl<'db, F: FileBackend> ReadTxn<'db, F>

pub fn begin(env: &'db TxnEnv<F>) -> Result<Self>

Begin a new read transaction.

Acquires a cross-process reader-lock slot (if env.lock_file is Some) with the env’s default busy timeout, then takes a ReaderSnapshot from the pager. Readers do not contend with each other (31 shared slots) and do not contend with writers on the byte-range layer.

Errors

• Error::Busy with LockKind::Reader on lock timeout.
• Error::Io on lock or pager syscall failure.

pub fn begin_with_timeout( env: &'db TxnEnv<F>, timeout: Duration, ) -> Result<Self>

As begin with a caller-supplied timeout.

Errors

See begin.

pub fn pinned_lsn(&self) -> Lsn

LSN this txn’s snapshot pinned. Diagnostic-only.

pub fn read_page(&self, id: PageId) -> Result<Page>

Read page id consistent with the txn’s snapshot.

Errors

As ReaderSnapshot::read_page.

pub fn snapshot(&self) -> &ReaderSnapshot<F>

Access the underlying snapshot. Used by obj::Db (M6 issue #47) to dispatch typed reads on a read txn.

pub fn env(&self) -> &TxnEnv<F>

Access the env this txn lives in. Used by obj::Db to access the pager mutex.

pub fn end(self)

Drop the txn explicitly (releases the snapshot pin and the reader lock).

Trait Implementations

impl<'db, F: Debug + FileBackend> Debug for ReadTxn<'db, F>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.