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.
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
We have almost 1000 lines of code related to Completions the
`io/mod.rs`. My intention here is to declutter the file so that we can
focus more on what is relevant for the `IO` and `File` trait
Closes#3800
