feat(260): Add index scans for equality predicates to query engine (#295

)

Fixes #260.

crates/core/src/database_instance_context_controller.rs

@@ -15,17 +15,20 @@ impl DatabaseInstanceContextController {
         Self::default()
     }
 
+    #[tracing::instrument(skip_all)]
     pub fn get(&self, database_instance_id: u64) -> Option<(Arc<DatabaseInstanceContext>, Scheduler)> {
         let contexts = self.contexts.lock().unwrap();
         contexts.get(&database_instance_id).cloned()
     }
 
+    #[tracing::instrument(skip_all)]
     pub fn insert(&self, database_instance_context: Arc<DatabaseInstanceContext>, scheduler: Scheduler) {
         let database_instance_id = database_instance_context.database_instance_id;
         let mut contexts = self.contexts.lock().unwrap();
         contexts.insert(database_instance_id, (database_instance_context, scheduler));
     }
 
+    #[tracing::instrument(skip_all)]
     pub fn remove(&self, database_instance_id: u64) -> Option<(Arc<DatabaseInstanceContext>, Scheduler)> {
         let mut contexts = self.contexts.lock().unwrap();
         contexts.remove(&database_instance_id)

crates/core/src/db/cursor.rs

@@ -2,7 +2,7 @@ use crate::error::DBError;
 use spacetimedb_lib::relation::{DbTable, RowCount};
 use spacetimedb_sats::ProductValue;
 
-use super::datastore::locking_tx_datastore::Iter;
+use super::datastore::locking_tx_datastore::{Iter, IterByColEq};
 
 #[derive(Debug, Clone, Copy)]
 pub enum CatalogKind {
@@ -24,6 +24,19 @@ impl<'a> TableCursor<'a> {
     }
 }
 
+/// A relational iterator wrapping a storage level index iterator.
+/// A relational iterator returns [RelValue]s whereas storage iterators return [DataRef]s.
+pub struct IndexCursor<'a> {
+    pub table: DbTable,
+    pub iter: IterByColEq<'a>,
+}
+
+impl<'a> IndexCursor<'a> {
+    pub fn new(table: DbTable, iter: IterByColEq<'a>) -> Result<Self, DBError> {
+        Ok(Self { table, iter })
+    }
+}
+
 /// Common wrapper for relational iterators of [Catalog].
 pub struct CatalogCursor<I> {
     pub(crate) table: DbTable,

crates/core/src/db/datastore/locking_tx_datastore/btree_index.rs

@@ -142,7 +142,7 @@ impl BTreeIndex {
     ///
     /// For a unique index this will always yield at most one `RowId`.
     #[tracing::instrument(skip_all)]
-    pub(crate) fn seek<'a>(&'a self, value: &'a AlgebraicValue) -> BTreeIndexRangeIter<'a> {
+    pub(crate) fn seek<'a>(&'a self, value: &AlgebraicValue) -> BTreeIndexRangeIter<'a> {
         let k_start = IndexKey::from_row(value, DataKey::min_datakey());
         let k_end = IndexKey::from_row(value, DataKey::max_datakey());
         BTreeIndexRangeIter {