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Merge 'Account divider cell in size while distributing cells' from Pere Diaz Bou

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~~Moving cells from right to left involves moving cell that are from any
page in the right, from left to right, this means we update the size of
page of adjacent one only but not the last one. This is kinda weird but
it works. I might change it if it feels to weird.~~
Update: my previous analysis was obviously incorrect. Underflowing is
undesired behaviour and accounting for divider cell avoided it.

Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>

Closes #1269
This commit is contained in:
Pere Diaz Bou
2025-04-08 16:42:16 +02:00
parent 0ec12b0192 fded6ccaf3
commit e368cd1499
1 changed files with 17 additions and 18 deletions
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35
core/storage/btree.rs
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@@ -1624,7 +1624,7 @@ impl BTreeCursor {
}
}
// calculate how many pages to allocate
let mut new_page_sizes = Vec::new();
let mut new_page_sizes: Vec<usize> = Vec::new();
let leaf_correction = if leaf { 4 } else { 0 };
// number of bytes beyond header, different from global usableSapce which includes
// header
@@ -1637,11 +1637,16 @@ impl BTreeCursor {
let page_contents = page.get_contents();
let free_space = compute_free_space(page_contents, self.usable_space() as u16);
new_page_sizes.push(usable_space as u16 - free_space);
new_page_sizes.push(usable_space as usize - free_space as usize);
for overflow in &page_contents.overflow_cells {
let size = new_page_sizes.last_mut().unwrap();
// 2 to account of pointer
*size += 2 + overflow.payload.len() as u16;
*size += 2 + overflow.payload.len() as usize;
}
if !leaf && i < balance_info.sibling_count - 1 {
// Account for divider cell which is included in this page.
let size = new_page_sizes.last_mut().unwrap();
*size += cell_array.cells[cell_array.cell_count(i)].len() as usize;
}
}
@@ -1650,7 +1655,7 @@ impl BTreeCursor {
let mut i = 0;
while i < sibling_count_new {
// First try to move cells to the right if they do not fit
while new_page_sizes[i] > usable_space as u16 {
while new_page_sizes[i] > usable_space as usize {
let needs_new_page = i + 1 >= sibling_count_new;
if needs_new_page {
sibling_count_new += 1;
@@ -1664,7 +1669,7 @@ impl BTreeCursor {
);
}
let size_of_cell_to_remove_from_left =
2 + cell_array.cells[cell_array.cell_count(i) - 1].len() as u16;
2 + cell_array.cells[cell_array.cell_count(i) - 1].len() as usize;
new_page_sizes[i] -= size_of_cell_to_remove_from_left;
let size_of_cell_to_move_right = if !leaf_data {
if cell_array.number_of_cells_per_page[i]
@@ -1672,23 +1677,23 @@ impl BTreeCursor {
{
// This means we move to the right page the divider cell and we
// promote left cell to divider
2 + cell_array.cells[cell_array.cell_count(i)].len() as u16
2 + cell_array.cells[cell_array.cell_count(i)].len() as usize
} else {
0
}
} else {
size_of_cell_to_remove_from_left
};
new_page_sizes[i + 1] += size_of_cell_to_move_right;
new_page_sizes[i + 1] += size_of_cell_to_move_right as usize;
cell_array.number_of_cells_per_page[i] -= 1;
}
// Now try to take from the right if we didn't have enough
while cell_array.number_of_cells_per_page[i] < cell_array.cells.len() as u16 {
let size_of_cell_to_remove_from_right =
2 + cell_array.cells[cell_array.cell_count(i)].len() as u16;
2 + cell_array.cells[cell_array.cell_count(i)].len() as usize;
let can_take = new_page_sizes[i] + size_of_cell_to_remove_from_right
> usable_space as u16;
> usable_space as usize;
if can_take {
break;
}
@@ -1699,7 +1704,7 @@ impl BTreeCursor {
if cell_array.number_of_cells_per_page[i]
< cell_array.cells.len() as u16
{
2 + cell_array.cells[cell_array.cell_count(i)].len() as u16
2 + cell_array.cells[cell_array.cell_count(i)].len() as usize
} else {
0
}
@@ -1745,8 +1750,8 @@ impl BTreeCursor {
// the same we add to right (we don't add divider to right).
let mut cell_right = cell_left + 1 - leaf_data as u16;
loop {
let cell_left_size = cell_array.cell_size(cell_left as usize);
let cell_right_size = cell_array.cell_size(cell_right as usize);
let cell_left_size = cell_array.cell_size(cell_left as usize) as usize;
let cell_right_size = cell_array.cell_size(cell_right as usize) as usize;
// TODO: add assert nMaxCells
let pointer_size = if i == sibling_count_new - 1 { 0 } else { 2 };
@@ -4735,9 +4740,7 @@ mod tests {
let (pager, root_page) = empty_btree();
let mut cursor = BTreeCursor::new(None, pager.clone(), root_page);
let mut keys = Vec::new();
let seed = rng.next_u64();
tracing::info!("seed: {}", seed);
let mut rng = ChaCha8Rng::seed_from_u64(seed);
for insert_id in 0..inserts {
let size = size(&mut rng);
let key = {
@@ -4875,25 +4878,21 @@ mod tests {
}
#[test]
#[ignore]
pub fn btree_insert_fuzz_run_random() {
btree_insert_fuzz_run(128, 16, |rng| (rng.next_u32() % 4096) as usize);
}
#[test]
#[ignore]
pub fn btree_insert_fuzz_run_small() {
btree_insert_fuzz_run(1, 100, |rng| (rng.next_u32() % 128) as usize);
}
#[test]
#[ignore]
pub fn btree_insert_fuzz_run_big() {
btree_insert_fuzz_run(64, 32, |rng| 3 * 1024 + (rng.next_u32() % 1024) as usize);
}
#[test]
#[ignore]
pub fn btree_insert_fuzz_run_overflow() {
btree_insert_fuzz_run(64, 32, |rng| (rng.next_u32() % 32 * 1024) as usize);
}