on the main branch, mvcc allows concurrent inserts from multiple
txns even without BEGIN CONCURRENT, and then always hangs whenever
one of the txns tries to commit.
this commit fixes that issue.
Flushing mvcc changes to disk requires serialization. To do so we simply
introduce a lock for pager.end_tx, which will take ownership of flushing
to WAL. Once this is finished we can simply release lock.
Currently, when MVCC is enabled, every transaction mode supports
concurrent reads and writes, which makes it hard to adopt for existing
applications that use `BEGIN DEFERRED` or `BEGIN IMMEDIATE`.
Therefore, add support for `BEGIN CONCURRENT` transactions when MVCC is
enabled. The transaction mode allows multiple concurrent read/write
transactions that don't block each other, with conflicts resolved at
commit time. Furthermore, implement the correct semantics for `BEGIN
DEFERRED` and `BEGIN IMMEDIATE` by taking advantage of the pager level
write lock when transaction upgrades to write. This means that now
concurrent MVCC transactions are serialized against the legacy ones when
needed.
The implementation includes:
- Parser support for CONCURRENT keyword in BEGIN statements
- New Concurrent variant in TransactionMode to distinguish from regular
read/write transactions
- MVCC store tracking of exclusive transactions to support IMMEDIATE and
EXCLUSIVE modes alongside CONCURRENT
- Proper transaction state management for all transaction types in MVCC
This enables better concurrency for applications that can handle
optimistic concurrency control, while still supporting traditional
SQLite transaction semantics via IMMEDIATE and EXCLUSIVE modes.
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Closes#3021
Currently, when MVCC is enabled, every transaction mode supports
concurrent reads and writes, which makes it hard to adopt for existing
applications that use `BEGIN DEFERRED` or `BEGIN IMMEDIATE`.
Therefore, add support for `BEGIN CONCURRENT` transactions when MVCC is
enabled. The transaction mode allows multiple concurrent read/write
transactions that don't block each other, with conflicts resolved at
commit time. Furthermore, implement the correct semantics for `BEGIN
DEFERRED` and `BEGIN IMMEDIATE` by taking advantage of the pager level
write lock when transaction upgrades to write. This means that now
concurrent MVCC transactions are serialized against the legacy ones when
needed.
The implementation includes:
- Parser support for CONCURRENT keyword in BEGIN statements
- New Concurrent variant in TransactionMode to distinguish from regular
read/write transactions
- MVCC store tracking of exclusive transactions to support IMMEDIATE and
EXCLUSIVE modes alongside CONCURRENT
- Proper transaction state management for all transaction types in MVCC
This enables better concurrency for applications that can handle
optimistic concurrency control, while still supporting traditional
SQLite transaction semantics via IMMEDIATE and EXCLUSIVE modes.
The `run_once()` name is just a historical accident. Furthermore, it now
started to appear elsewhere as well, so let's just call it IO::step() as we
should have from the beginning.
We were storing `txid` in `ProgramState`, this meant it was impossible
to track interactive transactions. This was extracted to `Connection`
instead.
Moreover, transaction state for mvcc now is reset on commit.
Closes#2689
This PR tries to add simple support for delete, with limited testing for
now.
Moreover, there was an error with `forward`, which wasn't obvious
without delete, which didn't skip deleted rows.
Reviewed-by: Avinash Sajjanshetty (@avinassh)
Closes#2672
This not only changes schema_did_change on commit_txn for mvcc, but also
extracts the connection transaction state from non mvcc transactions to
mvcc too.
