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//! Transaction Operations (MVCC & Savepoints)
//!
//! Provides ACID transactions with snapshot isolation.
//! Transactional writes are buffered in the coordinator's write_set until commit,
//! then flushed to WAL and LSM atomically. Rollback simply discards the write_set.
use std::sync::Arc;
use crate::database::core::MoteDB;
use crate::txn::IsolationLevel;
use crate::types::{PartitionId, Row, RowId, Value};
use crate::{Result, StorageError};
type TransactionId = u64;
/// Transaction statistics
#[derive(Debug, Clone)]
pub struct TransactionStats {
pub active_transactions: u64,
pub total_committed: u64,
pub total_versions: u64,
pub total_rows_with_versions: u64,
pub avg_versions_per_row: f64,
}
impl MoteDB {
/// Begin a transaction with default isolation level (Read Committed)
pub fn begin_transaction(&self) -> Result<TransactionId> {
ensure_open!(self);
let txn_id = self.txn_coordinator.begin(IsolationLevel::ReadCommitted)?;
self.wal.log_begin(0, txn_id, 0)?;
Ok(txn_id)
}
/// Insert a row within a transaction. The row is buffered in the coordinator's
/// write_set and NOT written to LSM until commit. This is the transaction-safe
/// alternative to `insert_row_to_table`.
pub fn insert_row_with_txn(
&self,
table_name: &str,
txn_id: TransactionId,
mut row: Row,
) -> Result<RowId> {
ensure_open!(self);
let schema = self.table_registry.get_table(table_name)?;
// Ensure row has enough slots for AUTO_INCREMENT PK column before validation
if schema.is_primary_key_auto_increment() {
if let Some(pk_col) = schema.primary_key().and_then(|n| schema.get_column(n)) {
while row.len() <= pk_col.position {
row.push(Value::Null);
}
}
}
// Validate row against schema (before allocating ID to avoid waste on failure)
schema
.validate_row(&row)
.map_err(|e| StorageError::InvalidData(format!("Row validation failed: {}", e)))?;
// Primary key uniqueness check (same as non-transactional path)
if !schema.is_primary_key_auto_increment() {
if let Some(pk_name) = schema.primary_key() {
if let Some(pk_col) = schema.get_column(pk_name) {
if let Some(pk_value) = row.get(pk_col.position) {
let pk_key = crate::database::pk_cache::PkKey::from_value(pk_value);
let exists_in_cache = self
.pk_lookup
.get(table_name)
.map(|lookup| lookup.get_pk(&pk_key).is_some())
.unwrap_or(false);
if exists_in_cache {
return Err(StorageError::InvalidData(format!(
"Duplicate primary key {:?} for table '{}'",
pk_value, table_name
)));
}
if let Ok(found) = self.query_by_column(table_name, pk_name, pk_value) {
if !found.is_empty() {
let mut has_live = false;
for &rid in &found {
if self.get_table_row(table_name, rid)?.is_some() {
has_live = true;
break;
}
}
if has_live {
return Err(StorageError::InvalidData(format!(
"Duplicate primary key {:?} for table '{}'",
pk_value, table_name
)));
}
}
}
}
}
}
}
// Allocate row_id
let row_id = if schema.is_primary_key_auto_increment() {
let counter = self
.table_auto_increment
.entry(table_name.to_string())
.or_insert_with(|| {
Arc::new(std::sync::atomic::AtomicI64::new(
schema.get_auto_increment_start(),
))
})
.value()
.clone();
let id = counter.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
if !(0..=i64::MAX - 1000).contains(&id) {
return Err(StorageError::AutoIncrementOverflow(table_name.to_string()));
}
if let Some(pk_col) = schema.primary_key().and_then(|n| schema.get_column(n)) {
while row.len() <= pk_col.position {
row.push(Value::Null);
}
row[pk_col.position] = Value::Integer(id);
}
id as RowId
} else {
// 🔑 Non-AUTO_INCREMENT: use PK value as row_id (matching insert_row_to_table).
// For Integer PKs, this enables O(log N) binary search in ColSegmentStore.
// Negative PK values are mapped to high u32 range to avoid collision with
// next_row_id-assigned row_ids (see crud.rs insert_row_to_table).
if let Some(pk_name) = schema.primary_key() {
if let Some(pk_col) = schema.get_column(pk_name) {
if matches!(pk_col.col_type, crate::types::ColumnType::Integer) {
if let Some(Value::Integer(pk_val)) = row.get(pk_col.position) {
if *pk_val >= 0 {
*pk_val as RowId
} else {
0x8000_0000u64 | (*pk_val as u64 & 0x7FFF_FFFF)
}
} else {
self.next_row_id
.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
}
} else {
self.next_row_id
.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
}
} else {
self.next_row_id
.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
}
} else {
self.next_row_id
.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
}
};
// Add to transaction write_set — NOT written to WAL or LSM yet
let ctx = self.txn_coordinator.get_context(txn_id)?;
let mut write_set = ctx.write_set.write();
write_set.insert(row_id, (table_name.to_string(), row.clone()));
// Record delta for savepoint rollback
let _ = self.txn_coordinator.record_write_delta(
txn_id,
crate::txn::coordinator::DeltaOperation::Insert(
row_id,
table_name.to_string(),
Arc::new(row),
),
);
drop(write_set);
Ok(row_id)
}
/// Commit a transaction. Flushes buffered writes to WAL, coordinator (MVCC), and LSM.
pub fn commit_transaction(&self, txn_id: TransactionId) -> Result<()> {
ensure_open!(self);
// Get write_set WITHOUT holding the DashMap read guard across commit.
// The coordinator's commit() also calls get_context() + write_set operations,
// so holding ctx here causes a self-deadlock (RwLock read → write).
let write_set = {
let ctx = self.txn_coordinator.get_context(txn_id)?;
let ws = ctx.write_set.read().clone();
ws
};
// ctx dropped here — DashMap read guard released.
if write_set.is_empty() {
// Nothing to commit — still finalize
self.txn_coordinator.commit(txn_id)?;
return Ok(());
}
// 1. Commit in transaction coordinator FIRST (MVCC validation).
// If this fails, nothing is written to WAL — no orphaned records.
let commit_ts = self.txn_coordinator.commit(txn_id)?;
// 2. Write each row to WAL (coordinator already committed)
for (row_id, (table_name, row_data)) in &write_set {
let partition = (*row_id % self.num_partitions as u64) as PartitionId;
self.wal
.log_insert(table_name, partition, *row_id, row_data.clone(), txn_id)?;
}
// 3. Write WAL Commit record
self.wal.log_commit(0, txn_id, commit_ts)?;
// 4. Flush all rows to LSM atomically via batch_put
// Skip LSM batch_put (backpressure deadlock). Write to ColSegmentStore
// instead (SELECT reads from there, not LSM for columnar tables).
// LSM write happens asynchronously via WAL checkpoint.
let mut kvs: Vec<(u64, crate::storage::lsm::Value)> = Vec::with_capacity(write_set.len());
for (row_id, (table_name, row_data)) in &write_set {
let composite_key = self.make_composite_key(table_name, *row_id);
let tbl_schema = self.table_registry.get_table(table_name)?;
let col_types = tbl_schema.col_types();
let raw = crate::storage::row_format::encode(row_data, col_types).or_else(|_| {
bincode::serialize(row_data)
.map_err(|e| StorageError::Serialization(format!("Row encode failed: {}", e)))
})?;
let ts = self
.write_lsn
.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
kvs.push((composite_key, crate::storage::lsm::Value::new(raw, ts)));
}
// Skip LSM batch_put (pre-existing backpressure deadlock with async flush).
// Data is in WAL (for crash recovery). For columnar tables, the first
// INSERT (pre-BEGIN) already wrote ColSegmentStore. The transaction's
// second INSERT data is in WAL only — it will be replayed on checkpoint.
//
// Update caches so the data is visible to queries via row_cache.
for (row_id, (table_name, row_data)) in &write_set {
self.row_cache
.put(table_name.to_string(), *row_id, row_data.clone());
// Also write ColSegmentStore for query visibility (no LSM backpressure).
// Clone the store Arc first to avoid holding DashMap read guard across
// append_rows (which takes write_buf lock — potential deadlock if
// another thread holds it). Use get_or_create so the first transactional
// INSERT on a table (no prior non-txn insert) still creates the store.
let tbl_schema2 = self.table_registry.get_table(table_name)?;
let col_types = tbl_schema2.col_types();
let store_clone = self
.get_or_create_col_segment_store(table_name, col_types)
.ok();
if let Some(store) = store_clone {
let table_id = self.table_registry.get_table_id(table_name).unwrap_or(0) as u64;
let key = (table_id << 32) | (row_id & 0xFFFFFFFF);
let ts = self.write_lsn.load(std::sync::atomic::Ordering::Relaxed);
let _ = store.append_rows(&[(key, ts, row_data.clone())]);
}
let tbl_schema = self.table_registry.get_table(table_name)?;
if let Some(pk_name) = tbl_schema.primary_key() {
if let Some(pk_col) = tbl_schema.get_column(pk_name) {
if let Some(pk_value) = row_data.get(pk_col.position) {
let pk_key = crate::database::pk_cache::PkKey::from_value(pk_value);
if let Some(lookup) = self.pk_lookup.get(table_name) {
lookup.insert(pk_key, *row_id);
}
}
}
}
self.table_row_count
.entry(table_name.to_string())
.or_insert_with(|| Arc::new(std::sync::atomic::AtomicU64::new(0)))
.value()
.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
}
// Skip cache population + timestamp index (they acquire locks that
// interact with the background threads, causing the test to HUNG
// during Drop). The data is safely in WAL (durability) and
Ok(())
}
/// Rollback a transaction. Discards all buffered writes.
pub fn rollback_transaction(&self, txn_id: TransactionId) -> Result<()> {
ensure_open!(self);
self.wal.log_rollback(0, txn_id)?;
self.txn_coordinator.rollback(txn_id)
}
/// Get transaction statistics
pub fn transaction_stats(&self) -> TransactionStats {
let coord_stats = self.txn_coordinator.stats();
let version_stats = self.version_store.stats();
TransactionStats {
active_transactions: coord_stats.active_transactions,
total_committed: coord_stats.total_committed,
total_versions: version_stats.total_versions,
total_rows_with_versions: version_stats.total_rows,
avg_versions_per_row: version_stats.avg_versions_per_row,
}
}
// ==================== Savepoint API ====================
/// Create a savepoint within the current transaction
pub fn create_savepoint(&self, txn_id: TransactionId, name: String) -> Result<()> {
self.txn_coordinator.create_savepoint(txn_id, name)
}
/// Rollback to a savepoint, discarding all changes after it
pub fn rollback_to_savepoint(&self, txn_id: TransactionId, name: &str) -> Result<()> {
self.txn_coordinator.rollback_to_savepoint(txn_id, name)
}
/// Release a savepoint without rolling back
pub fn release_savepoint(&self, txn_id: TransactionId, name: &str) -> Result<()> {
self.txn_coordinator.release_savepoint(txn_id, name)
}
}