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Merge 'mvcc: comments and small cleanup' from Jussi Saurio

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Closes #930
This commit is contained in:
Jussi Saurio
2025-02-15 18:18:01 +02:00
parent 01f51a4c20 3826c540ae
commit aea8b416bc
2 changed files with 21 additions and 15 deletions
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34
core/mvcc/database/mod.rs
View File

@@ -318,8 +318,9 @@ impl<Clock: LogicalClock, T: Sync + Send + Clone + Debug + 'static> MvStore<Cloc
.ok_or(DatabaseError::NoSuchTransactionID(tx_id))?;
let tx = tx.value().read().unwrap();
assert_eq!(tx.state, TransactionState::Active);
let version_is_visible_to_current_tx = is_version_visible(&self.txs, &tx, rv);
if !version_is_visible_to_current_tx {
// A transaction cannot delete a version that it cannot see,
// nor can it conflict with it.
if !rv.is_visible_to(&tx, &self.txs) {
continue;
}
if is_write_write_conflict(&self.txs, &tx, rv) {
@@ -366,11 +367,14 @@ impl<Clock: LogicalClock, T: Sync + Send + Clone + Debug + 'static> MvStore<Cloc
assert_eq!(tx.state, TransactionState::Active);
if let Some(row_versions) = self.rows.get(&id) {
let row_versions = row_versions.value().read().unwrap();
for rv in row_versions.iter().rev() {
if is_version_visible(&self.txs, &tx, rv) {
tx.insert_to_read_set(id);
return Ok(Some(rv.row.clone()));
}
if let Some(rv) = row_versions
.iter()
.rev()
.filter(|rv| rv.is_visible_to(&tx, &self.txs))
.next()
{
tx.insert_to_read_set(id);
return Ok(Some(rv.row.clone()));
}
}
Ok(None)
@@ -534,7 +538,7 @@ impl<Clock: LogicalClock, T: Sync + Send + Clone + Debug + 'static> MvStore<Cloc
}
if let Some(TxTimestampOrID::TxID(id)) = row_version.end {
if id == tx_id {
// New version is valid UNTIL committing transaction's end timestamp
// Old version is valid UNTIL committing transaction's end timestamp
// See diagram on page 299: https://www.cs.cmu.edu/~15721-f24/papers/Hekaton.pdf
row_version.end = Some(TxTimestampOrID::Timestamp(end_ts));
self.insert_version_raw(
@@ -763,12 +767,14 @@ pub(crate) fn is_write_write_conflict<T>(
}
}
pub(crate) fn is_version_visible<T>(
txs: &SkipMap<TxID, RwLock<Transaction>>,
tx: &Transaction,
rv: &RowVersion<T>,
) -> bool {
is_begin_visible(txs, tx, rv) && is_end_visible(txs, tx, rv)
impl<T> RowVersion<T> {
pub fn is_visible_to(
&self,
tx: &Transaction,
txs: &SkipMap<TxID, RwLock<Transaction>>,
) -> bool {
is_begin_visible(txs, tx, self) && is_end_visible(txs, tx, self)
}
}
fn is_begin_visible<T>(

2
core/mvcc/database/tests.rs
View File

@@ -699,7 +699,7 @@ fn test_snapshot_isolation_tx_visible1() {
},
};
tracing::debug!("Testing visibility of {row_version:?}");
is_version_visible(&txs, &current_tx, &row_version)
row_version.is_visible_to(&current_tx, &txs)
};
// begin visible: transaction committed with ts < current_tx.begin_ts