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distinguish balance and balance_non_root

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`balance_non_root` should be as close as possible to `balance_non_root`
in SQLite. This commits extract `balance_non_root` from `balance` and
renames `balance_leaf` to `balance` as it enables future work on a
complete `balance_non_root` procedure.
This commit is contained in:
Pere Diaz Bou 2025-01-08 19:05:49 +01:00
parent 0ef4def900
commit 6802bb7e6a
1 changed files with 30 additions and 5 deletions
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35
core/storage/btree.rs
View file

@ -78,6 +78,7 @@ macro_rules! return_if_locked {
enum WriteState {
Start,
BalanceStart,
BalanceNonRoot,
BalanceGetParentPage,
BalanceMoveUp,
Finish,
@ -730,9 +731,10 @@ impl BTreeCursor {
}
}
WriteState::BalanceStart
| WriteState::BalanceNonRoot
| WriteState::BalanceMoveUp
| WriteState::BalanceGetParentPage => {
return_if_io!(self.balance_leaf());
return_if_io!(self.balance());
}
WriteState::Finish => {
self.write_info.state = WriteState::Start;
@ -882,7 +884,7 @@ impl BTreeCursor {
/// This is a naive algorithm that doesn't try to distribute cells evenly by content.
/// It will try to split the page in half by keys not by content.
/// Sqlite tries to have a page at least 40% full.
fn balance_leaf(&mut self) -> Result<CursorResult<()>> {
fn balance(&mut self) -> Result<CursorResult<()>> {
let state = &self.write_info.state;
match state {
WriteState::BalanceStart => {
@ -906,7 +908,31 @@ impl BTreeCursor {
self.balance_root();
return Ok(CursorResult::Ok(()));
}
debug!("Balancing leaf. leaf={}", current_page.get().id);
self.write_info.state = WriteState::BalanceNonRoot;
self.balance_non_root()
}
WriteState::BalanceNonRoot
| WriteState::BalanceGetParentPage
| WriteState::BalanceMoveUp => self.balance_non_root(),
_ => unreachable!("invalid balance leaf state {:?}", state),
}
}
fn balance_non_root(&mut self) -> Result<CursorResult<()>> {
let state = &self.write_info.state;
match state {
WriteState::Start => todo!(),
WriteState::BalanceStart => todo!(),
WriteState::BalanceNonRoot => {
// drop divider cells and find right pointer
// NOTE: since we are doing a simple split we only finding the pointer we want to update (right pointer).
// Right pointer means cell that points to the last page, as we don't really want to drop this one. This one
// can be a "rightmost pointer" or a "cell".
// we always asumme there is a parent
let current_page = self.stack.top();
debug!("balance_non_root(page={})", current_page.get().id);
// Copy of page used to reference cell bytes.
// This needs to be saved somewhere safe so taht references still point to here,
@ -1186,8 +1212,7 @@ impl BTreeCursor {
let _ = self.write_info.page_copy.take();
Ok(CursorResult::Ok(()))
}
_ => unreachable!("invalid balance leaf state {:?}", state),
WriteState::Finish => todo!(),
}
}