sql: use shared txn borrows during execution

src/sql/execution/execute.rs

@@ -10,7 +10,7 @@ use crate::sql::plan::{Node, Plan};
 use crate::sql::types::{Columns, Row, Rows};
 
 /// Executes a plan, returning an execution result.
-pub fn execute_plan(plan: Plan, txn: &mut impl Transaction) -> Result<ExecutionResult> {
+pub fn execute_plan(plan: Plan, txn: &impl Transaction) -> Result<ExecutionResult> {
  Ok(match plan {
  Plan::CreateTable { schema } => {
  let name = schema.name.clone();
@@ -49,7 +49,7 @@ pub fn execute_plan(plan: Plan, txn: &mut impl Transaction) -> Result<ExecutionR
 ///
 /// TODO: since iterators are lazy, make this infallible and move all catalog
 /// lookups to planning.
-pub fn execute(node: Node, txn: &mut impl Transaction) -> Result<QueryIterator> {
+pub fn execute(node: Node, txn: &impl Transaction) -> Result<QueryIterator> {
  match node {
  Node::Aggregation { source, aggregates } => {
  let source = execute(*source, txn)?;

src/sql/execution/schema.rs

@@ -3,12 +3,12 @@ use crate::sql::engine::Transaction;
 use crate::sql::types::schema::Table;
 
 // Creates a table (i.e. CREATE TABLE).
-pub(super) fn create_table(txn: &mut impl Transaction, schema: Table) -> Result<()> {
+pub(super) fn create_table(txn: &impl Transaction, schema: Table) -> Result<()> {
  txn.create_table(schema)
 }
 
 /// Deletes a table (i.e. DROP TABLE). Returns true if the table existed.
-pub(super) fn drop_table(txn: &mut impl Transaction, table: &str, if_exists: bool) -> Result<bool> {
+pub(super) fn drop_table(txn: &impl Transaction, table: &str, if_exists: bool) -> Result<bool> {
  // TODO the planner should deal with this.
  if if_exists && txn.get_table(table)?.is_none() {
  return Ok(false);

src/sql/execution/source.rs

@@ -5,7 +5,7 @@ use crate::sql::types::{Column, Expression, Row, Value};
 
 /// A table scan source.
 pub(super) fn scan(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  filter: Option<Expression>,
 ) -> Result<QueryIterator> {
@@ -19,7 +19,7 @@ pub(super) fn scan(
 
 /// A primary key lookup source.
 pub(super) fn lookup_key(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  keys: Vec<Value>,
 ) -> Result<QueryIterator> {
@@ -40,7 +40,7 @@ pub(super) fn lookup_key(
 
 /// An index lookup source.
 pub(super) fn lookup_index(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  column: &str,
  values: Vec<Value>,

src/sql/execution/write.rs

@@ -8,7 +8,7 @@ use crate::sql::types::{Expression, Row, Value};
 /// Deletes rows, taking primary keys from the source (i.e. DELETE).
 /// Returns the number of rows deleted.
 pub(super) fn delete(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  mut source: QueryIterator,
 ) -> Result<u64> {
@@ -26,7 +26,7 @@ pub(super) fn delete(
 ///
 /// TODO: this should take rows from a values source.
 pub(super) fn insert(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  columns: Vec<String>,
  values: Vec<Vec<Expression>>,
@@ -50,7 +50,7 @@ pub(super) fn insert(
 /// Updates rows passed in from the source (i.e. UPDATE). Returns the number of
 /// rows updated.
 pub(super) fn update(
- txn: &mut impl Transaction,
+ txn: &impl Transaction,
  table: &str,
  mut source: QueryIterator,
  expressions: Vec<(usize, Expression)>,