Backward scan of a table wasn't implemented yet in MVCC so this achieves
that. I added simple test for mixed btree and mvcc backward scan but I
should add more intense testing for this.
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> Implements backward scanning and last() in MVCC lazy cursor and adds
directional rowid iteration in the MVCC store, with new tests for mixed
MVCC+B-Tree backward scans.
>
> - **MVCC Cursor (`core/mvcc/cursor.rs`)**:
> - Implement `prev()` and `last()` with mixed MVCC/B-Tree
coordination using `IterationDirection`.
> - Add `PrevState` and extend state machine to handle backward
iteration.
> - Update `get_new_position_from_mvcc_and_btree(...)` to choose
rowids based on direction.
> - Integrate B-Tree cursor calls (`last`, `prev`) and adjust
`rewind`/rowid selection; tweak next-rowid when at `End`.
> - **MVCC Store (`core/mvcc/database/mod.rs`)**:
> - Add `get_prev_row_id_for_table(...)` and generalized
`get_row_id_for_table_in_direction(...)` supporting forward/backward
scans.
> - Add tracing and minor refactors around next/prev rowid retrieval.
> - **Tests (`core/mvcc/database/tests.rs`)**:
> - Add test for backward scan combining B-Tree and MVCC and an
ignored test covering delete during backward scan.
>
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<!-- /CURSOR_SUMMARY -->
Closes#3980
I've added a trait called `CursorTrait`. I know it's not a good name for
now, but I didn't know what tto change then enum `Cursor` to. This trait
wraps all common functionality, and some functionality that is yet too
specific that needs to be fixed.
This is needed in order to have layered cursors where for example,
MvccCursor will need a fallback BTreeCursor.
Closes#3660
Rollback shouldn't modify the row version chain. This is crucial for
implementing a Non-blocking row version chain in #3499
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#3583
Yield is a completion that does not allocate any inner state. By design
it is completed from the start and has no errors. This allows lightly
yield without allocating any locks nor heap allocate inner state.
This PR add proper program abort in case of unfinished statement reset
and interruption.
Also, this PR makes rollback methods non-failing because otherwise of
their callers usually unclear (if rollback failed - what is the state of
statement/connection/transaction?)
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#3591
For insert-heavy checkpoints this gives a much higher chance of using
the balance-quick subalgorithm instead of the more complex and slower
balance-nonroot.
Closes#3589
