closes#3811
adds `text_cache` which owns the null terminated bytes, which get cached
if a subsequent call to `sqlite3_column_text` is made.
#3809 depends on this fix
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#3817
This PR implements simple heap-sort approach for query plans like
`SELECT ... FROM t WHERE ... ORDER BY ... LIMIT N` in order to maintain
small set of top N elements in the ephemeral B-tree and avoid sort and
materialization of whole dataset.
I removed all optimizations not related to this particular change in
order to make branch lightweight.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#3726
## Gist
This PR implements _statement subtransactions_, which means that a
single statement within an interactive transaction can individually be
rolled back.
## Background
The default constraint violation resolution strategy in SQLite is
`ABORT`, which means to rollback the statement that caused the conflict.
For example:
```sql
CREATE TABLE t(x UNIQUE);
INSERT INTO t VALUES (1);
BEGIN;
INSERT INTO t VALUES (2),(3); -- ok
INSERT INTO t VALUES (4),(1); -- conflict on 1, this statement should rollback
INSERT INTO t VALUES (5); -- ok
COMMIT; -- ok
SELECT * FROM t;
1
2
3
5
```
So far we haven't been able to support this due to lack of support for
subtransactions, and have used the `ROLLBACK` strategy, which means to
rollback the entire transaction on any constraint error.
## Problem
Although PRIMARY KEY and UNIQUE constraints allow defining the conflict
resolution strategy (e.g. `id INTEGER PRIMARY KEY ON CONFLICT
ROLLBACK`), FOREIGN KEY violations do not support this: they always use
`ABORT` i.e. statement subtransaction rollback. For this reason alone it
is important to implement this mechanism now rather than later, since we
already have FOREIGN KEY support implemented.
## Details
This PR implements statement subtransactions with _anonymous
savepoints_. This means that whenever a statement begins, it will open a
new savepoint which will write "page undo images" into a temporary file
called a _subjournal_. Whenever the statement marks a page as dirty, it
will write the before-image of the page into the subjournal so that its
modifications can be undone in the event of an ABORT (statement
rollback).
- Right now, only anonymous savepoints are supported, so the explicit
`SAVEPOINT` syntax is not.
- Due to the above, there can be only one savepoint open per pager, and
this is enforced with assertions.
- The subjournal file is currently entirely in memory. If it were not,
we would either have to block on IO or refactor many usages of code to
account for potentially pending completions.
- Constraint errors no longer cause transactions to abort nor do they
cause the page cache to be cleared - instead, subjournaled pages will be
brought back into the page cache which effectively handles the same
behavior albeit more fine-grained.
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#3792
Every transaction was reading page 1 from the WAL to check the schema
cookie in op_transaction, causing unnecessary WAL lookups.
This commit caches the schema_cookie in Pager as AtomicU64, similar to
how page_size and reserved_space are already cached. The cache is
updated when the header is read/modified and invalidated in
begin_read_tx() when WAL changes are detected from other connections.
This matches SQLite's approach of caching frequently accessed header
fields to avoid repeated page 1 reads. Improves write throughput by 5%
in our benchmarks.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#3727
We don't want something like `BEGIN IMMEDIATE` to start a subtransaction,
so instead we will open it if:
- Statement is write, AND
a) Statement has >0 table_references, or
b) The statement is an INSERT (INSERT doesn't track table_references in
the same way as other program types)
- Add more statements per iteration
- Allow interactive transaction to contain multiple statements
- add VERBOSE flag to print all statements executed in a successful
iteration
The subjournal is a temporary file where stmt subtransactions write an
'undo log' of pages before modifying them. If a stmt subtransaction
rolls back, the pages are restored from the subjournal.
1. The number of deferred FK violations when the statement started.
When a statement subtransaction rolls back, the connection's
deferred violation counter will be reset to this value.
2. The number of immediate FK violations that occurred during the
statement. In practice we just need to know whether this number
is nonzero, and if it is, the statement subtransaction will roll
back.
Statement subtransactions will be implemented in future commits.
This PR adds the following derive macro
`AtomicEnum`
for the cases like the following:
```rust
pub enum SyncMode {
Off = 0,
Full = 2,
}
// or
pub enum CipherMode {
Aes128Gcm,
Aes256Gcm,
Aegis256,
Aegis128L,
Aegis128X2,
Aegis128X4,
Aegis256X2,
Aegis256X4,
}
```
Which are very basic enums, but which currently either require a
`RwLock` (the current solution for both of the above), or they require a
hand rolled atomic wrapper to keep the state without the lock.
```rust
pub struct AtomicDbState(AtomicUsize);
impl AtomicDbState {
#[inline]
pub const fn new(state: DbState) -> Self {
Self(AtomicUsize::new(state as usize))
}
```
This PR adds `AtomicEnum` derive macro which generates and let's us use
`AtomicDbState` or `AtomicCipherMode`, and derives `get`, `set` and
`swap` methods on them.
Each enum can have up to 1 named or unnamed field, and it supports i8/u8
and boolean types, which it encodes into half of a u16, with the
discriminant in the other half. Otherwise, it will just use a u8 and
encode the boolean into the 7th bit.
Closes#3766
Every transaction was reading page 1 from the WAL to check the schema cookie
in op_transaction, causing unnecessary WAL lookups.
This commit caches the schema_cookie in Pager as AtomicU64, similar to how
page_size and reserved_space are already cached. The cache is updated when the
header is read/modified and invalidated in begin_read_tx() when WAL changes
are detected from other connections.
This matches SQLite's approach of caching frequently accessed header fields to
avoid repeated page 1 reads. Improves write throughput by 5% in our
benchmarks.
