The built-in `unreachable!` macro, believe it or not is just an alias
for `panic!` and does not actually provide the compiler with a hint that
the path is not reachable.
This provides a wrapper around the actual
`std::hint::unreachable_unchecked()`, to be used only in the very hot
path of `execute` where it is not possible to be the incorrect variant.
Closes#2459
SQLite generates those in aggregations like min / max with collation
information either in the table definition or in the column expression.
We currently generate the wrong result here, and properly generating the
bytecode instruction fixes it.
Closes#2440
## Fix 1
Do not start a read transaction when a SELECT is not going to access the
database, which means we can avoid checking whether the schema has
changed.
## Fix 2
Add a field `accesses_db` to `Program` and `Statement` so we can avoid
even checking for `SchemaUpdated` errors when it's not possible to get
one.
## Fix 3
Avoid doing any work in `commit_txn` when not in a transaction. This
optimization is only enabled when `mv_store.is_none()`, because MVCC has
its own logic and this doesn't work with MVCC enabled, and honestly I'm
too tired to find out why. Left an inline comment about it, though.
```sql
Execute `SELECT 1`/limbo_execute_select_1
time: [21.440 ns 21.513 ns 21.586 ns]
change: [-60.766% -60.616% -60.453%] (p = 0.00 < 0.05)
Performance has improved.
```
Effect is even more dramatic in CI where the latency is down over 80%
Closes#2441
Closes#1967
To support this I had to change how we did `epilogue` similarly to how
SQLite does it. SQLIte first declares a `beginWriteOperation` when some
statement is going to necessitate a Write Transaction. And as we now
need to pass the current schema cookie to `epilogue` it was easier to
call epilogue only in one location (like we do with prologue), and just
have each statement declare their intentions separately. This allows us
to not have to pass the Schema around just to do the epilogue. I believe
this is something that @jussisaurio would be interested in.
~Also had to disable the MVCC test, as it was extremely buggy for me.~
Just disabled reprepare statements for MVCC
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#2214
Resolves#2378.
```
`ALTER TABLE _ RENAME TO _`/limbo_rename_table/
time: [15.645 ms 15.741 ms 15.850 ms]
Found 12 outliers among 100 measurements (12.00%)
8 (8.00%) high mild
4 (4.00%) high severe
`ALTER TABLE _ RENAME TO _`/sqlite_rename_table/
time: [34.728 ms 35.260 ms 35.955 ms]
Found 15 outliers among 100 measurements (15.00%)
8 (8.00%) high mild
7 (7.00%) high severe
```
<img width="1000" height="199" alt="image" src="https://github.com/user-
attachments/assets/ad943355-b57d-43d9-8a84-850461b8af41" />
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#2399
This will save some work when yielding to IO. Previously, on every
invocation, if the record was a packed record, we parsed it and iterated
through the values to check for nulls. Now, the pre-seeking work is done
only once.
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#2394
Unfortunately it seems we are never reaching the point to remove state
machines, so might as well make it easier to make.
There are two points that must be highlighted:
1. There is a `StateTransition` trait implemented like:
```rust
pub trait StateTransition {
type State;
type Context;
fn transition<'a>(&mut self, context: &Self::Context) ->
Result<TransitionResult>;
fn finalize<'a>(&mut self, context: &Self::Context) -> Result<()>;
fn is_finalized(&self) -> bool;
}
```
where there exists `transition` which tries to move state forward, and
`finalize` which marks the state machine as "finalized" so that **no
other call to finalize will forward the state and it will panic instead.
2. Before, we would store the state of a state machine inside the
callee's struct, but I'm proposing we do something different where the
callee will return the state machine and the caller will be responsible
of advancing it. This way we don't need to track many reset operations
in case of failures or rollbacks, and instead we could simply drop a
state machine and all other nested state machines will drop in a
cascade.
We need to load rowids into mvcc's store in order before doing any read
in case there are rows.
This has a performance penalty for now as expected because we should,
ideally, scan for row ids lazily instead.
