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.
Depends on #3584 to use the most up-to-date implementation of
`ThreadRng`
- Add `fill_bytes` method to `IO`
- use `thread_rng` instead of `getrandom`, as `getrandom` is much slower
and `thread_rng` offers enough security
- modify `exec_randomblob`, `exec_random` and random_rowid generation to
use methods from IO for determinism
- modified simulator IO to implement `fill_bytes`
This the PRNG for sqlite if someone is curious. It is similar to
`thread_rng`:
```c
/* Initialize the state of the random number generator once,
** the first time this routine is called.
*/
if( wsdPrng.s[0]==0 ){
sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
static const u32 chacha20_init[] = {
0x61707865, 0x3320646e, 0x79622d32, 0x6b206574
};
memcpy(&wsdPrng.s[0], chacha20_init, 16);
if( NEVER(pVfs==0) ){
memset(&wsdPrng.s[4], 0, 44);
}else{
sqlite3OsRandomness(pVfs, 44, (char*)&wsdPrng.s[4]);
}
wsdPrng.s[15] = wsdPrng.s[12];
wsdPrng.s[12] = 0;
wsdPrng.n = 0;
}
assert( N>0 );
while( 1 /* exit by break */ ){
if( N<=wsdPrng.n ){
memcpy(zBuf, &wsdPrng.out[wsdPrng.n-N], N);
wsdPrng.n -= N;
break;
}
if( wsdPrng.n>0 ){
memcpy(zBuf, wsdPrng.out, wsdPrng.n);
N -= wsdPrng.n;
zBuf += wsdPrng.n;
}
wsdPrng.s[12]++;
chacha_block((u32*)wsdPrng.out, wsdPrng.s);
wsdPrng.n = 64;
}
sqlite3_mutex_leave(mutex);
```
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Closes#3799
closes#3666
and probably other issues i'll have to go digging through to see if
there is any others.
<img width="948" height="445" alt="image" src="https://github.com/user-
attachments/assets/2844e09b-109a-4a70-bd18-d8a814e49ea0" />
Any ALTER COLUMN stmt will now update the constraints on the table
(primary key, foreign key, unique)
Closes#3776
DEFERRED was a bit too deferred - it allowed the dirty pages to be
written out to WAL before checking for violations, resulting in the
violations effectively being committed even though the transaction
ended up aborting
Rolling back a transaction on Error should result in
`connection.auto_commit` being set back to true.
Added a regression test for this where a UNIQUE constraint violation
rolls back the transaction and trying to COMMIT will fail.
Currently, our default conflict resolution strategy is ROLLBACK, which
ends the transaction. In SQLite, the default is ABORT, which rolls back
the current statement but allows the transaction to continue.
We should migrate to default ABORT once we support subtransactions.
Closes#3746
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#3747
Rolling back a transaction should result in `connection.auto_commit` being set
back to true.
Added a regression test for this where a UNIQUE constraint violation rolls back
the transaction and trying to COMMIT will fail.
Currently, our default conflict resolution strategy is ROLLBACK,
which ends the transaction. In SQLite, the default is ABORT, which rolls back
the current statement but allows the transaction to continue.
We should migrate to default ABORT once we support subtransactions.
This patch pushes unsafe Send and Sync to individual components instead
of doing it at Database level. This makes it easier for us to
incrementally fix thread-safety, but avoid developers adding more thread
unsafe code.
This PR introduces a `Context` object that is stored in the `Completion`
that currently only stores a `Waker`. In the future, I want to add some
sort of abort signal so that we can abort tasks that share the same
Context. To pass the Waker, I introduced a `step_with_waker` function in
`Statement` that delegates to an internal `_step` function. `_step` is
the previous `step` but just with the `Option<&Waker>` argument.
I was going to try and have the BusyHandler by truly async as well, but
I decided to not do it here, because it will be slightly complicated to
achieve.
Closes#3535
Closes#3687 .
Previously, the `try_fold_expr_to_i64` function casted `NULL` as `0`
when evaluating expressions in `LIMIT` or `OFFSET` clauses. I removed
this function since evaluating the expression directly and relying on
the MustBeInt operation for casting seems to handle everything.
Closes#3695
We merged two concurrent fixes to `nchange` handling last night and
AFAICT the fix in #3692 was incorrect because it doesn't count UPDATEs
in cases where the original row was DELETEd as part of the UPDATE
statement.
The correct fix was in 87434b8
Closes#2600
## Problem
Every btree has a key it is sorted by - this is the integer `rowid` for
tables and an arbitrary-sized, potentially multi-column key for indexes.
Executing an UPDATE in a loop is not safe if the update modifies any
part of the key of the btree that is used for iterating the rows in said
loop. For example:
- Using the table itself to iterate rows is not safe if the UPDATE
modifies the rowid (or rowid alias) of a row, because since it modifies
the iteration order itself, it may cause rows to be skipped:
```sql
CREATE TABLE t(x INTEGER PRIMARY KEY, y);
INSERT <something>
UPDATE t SET y = RANDOM() where x > 100; // safe to iterate 't', 'y' is not being modified
UPDATE t SET x = RANDOM() where x > 100; // not safe to iterate 't', 'x' is being modified
```
- Using an index to iterate rows is not safe if the UPDATE modifies any
of the columns in the index key
```sql
CREATE TABLE t(x, y, z);
CREATE INDEX txy ON t (x,y);
INSERT <something>
UPDATE t SET z = RANDOM() where x = 100 and y > 0; // safe to iterate txy, neither x or y is being modified
UPDATE t SET x = RANDOM() where x = 100 and y > 0; // not safe to iterate txy, 'x' is being modified
UPDATE t SET y = RANDOM() where x = 100 and y > 0; // not safe to iterate txy, 'y' is being modified
```
## Current solution in tursodb
Our current `main` code recognizes this issue and adopts this pseudocode
algorithm from SQLite:
- open a table or index for reading the rows of the source table,
- for each row that matches the condition in the UPDATE statement, write
the row into a temporary table
- then use that temporary table for iteration in the UPDATE loop.
This guarantees that the iteration order will not be affected by the
UPDATEs because the ephemeral table is not under modification.
## Problem with current solution
Our `main` code specialcases the ephemeral table solution to rowids /
rowid aliases only. Using indexes for UPDATE iteration was disabled in
an earlier PR (#2599) due to the safety issue mentioned above, which
means that many UPDATE statements become full table scans:
```sql
turso> create table t(x PRIMARY KEY);
turso> insert into t select value from generate_series(1,10000);
turso> explain update t set x = x + 100000 where x > 50 and x < 60;
addr opcode p1 p2 p3 p4 p5 comment
---- ----------------- ---- ---- ---- ------------- -- -------
0 Init 0 28 0 0 Start at 28
1 OpenWrite 0 2 0 0 root=2; iDb=0
2 OpenWrite 1 3 0 0 root=3; iDb=0
-- scan entire 't' despite very narrow update range!
3 Rewind 0 27 0 0 Rewind table t
...
```
## Solution
We move the ephemeral table logic to _after_ the optimizer has selected
the best access path for the table, and then, if the UPDATE modifies the
key of the chosen access path (table or index; whichever was selected by
the optimizer), we change the plan to include the ephemeral table
prepopulation. Hence, the same query from above becomes:
```sql
turso> explain update t set x = x + 100000 where x > 50 and x < 60;
addr opcode p1 p2 p3 p4 p5 comment
---- ----------------- ---- ---- ---- ------------- -- -------
0 Init 0 35 0 0 Start at 35
1 OpenEphemeral 0 1 0 0 cursor=0 is_table=true
2 OpenRead 1 3 0 0 index=sqlite_autoindex_t_1, root=3, iDb=0
3 Integer 50 2 0 0 r[2]=50
-- index seek on PRIMARY KEY index
4 SeekGT 1 10 2 0 key=[2..2]
5 Integer 60 2 0 0 r[2]=60
6 IdxGE 1 10 2 0 key=[2..2]
7 IdxRowId 1 1 0 0 r[1]=cursor 1 for index sqlite_autoindex_t_1.rowid
8 Insert 0 3 1 ephemeral_scratch 2 intkey=r[1] data=r[3]
9 Next 1 6 0 0
10 OpenWrite 2 2 0 0 root=2; iDb=0
11 OpenWrite 3 3 0 0 root=3; iDb=0
-- only scan rows that were inserted to ephemeral index
12 Rewind 0 34 0 0 Rewind table ephemeral_scratch
13 RowId 0 5 0 0 r[5]=ephemeral_scratch.rowid
```
Note that an ephemeral index does not have to be used if the index is
not affected:
```sql
turso> create table t(x PRIMARY KEY, data);
turso> explain update t set data = 'some_data' where x > 50 and x < 60;
addr opcode p1 p2 p3 p4 p5 comment
---- ----------------- ---- ---- ---- ------------- -- -------
0 Init 0 15 0 0 Start at 15
1 OpenWrite 0 2 0 0 root=2; iDb=0
2 OpenWrite 1 3 0 0 root=3; iDb=0
3 Integer 50 1 0 0 r[1]=50
-- direct index seek
4 SeekGT 1 14 1 0 key=[1..1]
```
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#3728
When populating an ephemeral table for UPDATE, it may open a cursor
on the (permanent) table - in this case we don't need to open it
again in the UPDATE loop
We currently return the exact same error from two different IdxDelete
paths. Improve the messages with context about what we're doing to make
this error more debuggable.
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
This PR introduces sparse vectors support and jaccard distance
implementation.
Also, this PR restructure the code to have all vector operations in
separate files (they grow pretty quickly as new vector representations
added to the DB).
Closes#3647
Various little fixes to `Sorter` that reduce unnecessary work.
Makes TPC-H query 1 roughly 2x faster, which is a lot because it
originally took 30-40 seconds depending on the CI run
Closes#3645
I found an application in the open that expects sqlite_version() to
return a specific string (higher than 3.8...).
We had tons of those issues at Scylla, and the lesson was that you tell
your kids not to lie, but when life hits, well... you lie.
We'll add a new function, turso_version, that tells the truth.
Closes#3635
