Select count table scan optimisation (#4285)

core/src/dbs/iterator.rs

@@ -27,7 +27,7 @@ const TARGET: &str = "surrealdb::core::dbs";
 #[derive(Clone)]
 pub(crate) enum Iterable {
 	Value(Value),
-	Table(Table),
+	Table(Table, bool), // true = keys only
 	Thing(Thing),
 	TableRange(String, IdRange),
 	Edges(Edges),
@@ -126,7 +126,7 @@ impl Iterator {
 					}
 					_ => {
 						// Ingest the table for scanning
-						self.ingest(Iterable::Table(v))
+						self.ingest(Iterable::Table(v, false))
 					}
 				},
 				// There is no data clause so create a record id
@@ -137,7 +137,7 @@ impl Iterator {
 					}
 					_ => {
 						// Ingest the table for scanning
-						self.ingest(Iterable::Table(v))
+						self.ingest(Iterable::Table(v, false))
 					}
 				},
 			},

core/src/dbs/plan.rs

@@ -93,8 +93,13 @@ impl ExplainItem {
 				name: "Iterate Value".into(),
 				details: vec![("value", v.to_owned())],
 			},
-			Iterable::Table(t) => Self {
-				name: "Iterate Table".into(),
+			Iterable::Table(t, keys_only) => Self {
+				name: if *keys_only {
+					"Iterate Table Keys"
+				} else {
+					"Iterate Table"
+				}
+				.into(),
 				details: vec![("table", Value::from(t.0.to_owned()))],
 			},
 			Iterable::Thing(t) => Self {

core/src/dbs/processor.rs

@@ -16,6 +16,7 @@ use crate::sql::{Edges, Table, Thing, Value};
 use channel::Sender;
 use futures::StreamExt;
 use reblessive::tree::Stk;
+use std::borrow::Cow;
 use std::ops::Bound;
 use std::vec;
 
@@ -55,7 +56,7 @@ impl Iterable {
 
 	fn iteration_stage_check(&self, ctx: &Context) -> bool {
 		match self {
-			Iterable::Table(tb) | Iterable::Index(tb, _) => {
+			Iterable::Table(tb, _) | Iterable::Index(tb, _) => {
 				if let Some(IterationStage::BuildKnn) = ctx.get_iteration_stage() {
 					if let Some(qp) = ctx.get_query_planner() {
 						if let Some(exe) = qp.get_query_executor(tb) {
@@ -111,6 +112,19 @@ impl<'a> Processor<'a> {
 		Ok(())
 	}
 
+	fn check_query_planner_context<'b>(ctx: &'b Context, table: &'b Table) -> Cow<'b, Context> {
+		if let Some(qp) = ctx.get_query_planner() {
+			if let Some(exe) = qp.get_query_executor(&table.0) {
+				// We set the query executor matching the current table in the Context
+				// Avoiding search in the hashmap of the query planner for each doc
+				let mut ctx = MutableContext::new(ctx);
+				ctx.set_query_executor(exe.clone());
+				return Cow::Owned(ctx.freeze());
+			}
+		}
+		Cow::Borrowed(ctx)
+	}
+
 	async fn process_iterable(
 		&mut self,
 		stk: &mut Stk,
@@ -128,18 +142,13 @@ impl<'a> Processor<'a> {
 					self.process_range(stk, ctx, opt, stm, tb, v).await?
 				}
 				Iterable::Edges(e) => self.process_edge(stk, ctx, opt, stm, e).await?,
-				Iterable::Table(v) => {
-					if let Some(qp) = ctx.get_query_planner() {
-						if let Some(exe) = qp.get_query_executor(&v.0) {
-							// We set the query executor matching the current table in the Context
-							// Avoiding search in the hashmap of the query planner for each doc
-							let mut ctx = MutableContext::new(ctx);
-							ctx.set_query_executor(exe.clone());
-							let ctx = ctx.freeze();
-							return self.process_table(stk, &ctx, opt, stm, &v).await;
-						}
+				Iterable::Table(v, keys_only) => {
+					let ctx = Self::check_query_planner_context(ctx, &v);
+					if keys_only {
+						self.process_table_keys(stk, &ctx, opt, stm, &v).await?
+					} else {
+						self.process_table(stk, &ctx, opt, stm, &v).await?
 					}
-					self.process_table(stk, ctx, opt, stm, &v).await?
 				}
 				Iterable::Index(t, irf) => {
 					if let Some(qp) = ctx.get_query_planner() {
@@ -340,6 +349,45 @@ impl<'a> Processor<'a> {
 		Ok(())
 	}
 
+	async fn process_table_keys(
+		&mut self,
+		stk: &mut Stk,
+		ctx: &Context,
+		opt: &Options,
+		stm: &Statement<'_>,
+		v: &Table,
+	) -> Result<(), Error> {
+		// Get the transaction
+		let txn = ctx.tx();
+		// Check that the table exists
+		txn.check_ns_db_tb(opt.ns()?, opt.db()?, v, opt.strict).await?;
+		// Prepare the start and end keys
+		let beg = thing::prefix(opt.ns()?, opt.db()?, v);
+		let end = thing::suffix(opt.ns()?, opt.db()?, v);
+		// Create a new iterable range
+		let mut stream = txn.stream_keys(beg..end);
+		// Loop until no more entries
+		while let Some(res) = stream.next().await {
+			// Check if the context is finished
+			if ctx.is_done() {
+				break;
+			}
+			// Parse the data from the store
+			let k = res?;
+			let key: thing::Thing = (&k).into();
+			let rid = Thing::from((key.tb, key.id));
+			// Process the record
+			let pro = Processed {
+				rid: Some(rid.into()),
+				ir: None,
+				val: Operable::Value(Value::Null.into()),
+			};
+			self.process(stk, ctx, opt, stm, pro).await?;
+		}
+		// Everything ok
+		Ok(())
+	}
+
 	async fn process_range(
 		&mut self,
 		stk: &mut Stk,

core/src/idx/planner/mod.rs

@@ -14,18 +14,34 @@ use crate::idx::planner::iterators::IteratorRef;
 use crate::idx::planner::knn::KnnBruteForceResults;
 use crate::idx::planner::plan::{Plan, PlanBuilder};
 use crate::idx::planner::tree::Tree;
+use crate::sql::statements::SelectStatement;
 use crate::sql::with::With;
-use crate::sql::{Cond, Orders, Table};
+use crate::sql::{Cond, Fields, Groups, Orders, Table};
 use reblessive::tree::Stk;
 use std::collections::HashMap;
 use std::sync::atomic::{AtomicU8, Ordering};
-use std::sync::Arc;
+
+pub(crate) struct QueryPlannerParams<'a> {
+	fields: &'a Fields,
+	with: Option<&'a With>,
+	order: Option<&'a Orders>,
+	cond: Option<&'a Cond>,
+	group: Option<&'a Groups>,
+}
+
+impl<'a> From<&'a SelectStatement> for QueryPlannerParams<'a> {
+	fn from(stmt: &'a SelectStatement) -> Self {
+		QueryPlannerParams {
+			fields: &stmt.expr,
+			with: stmt.with.as_ref(),
+			order: stmt.order.as_ref(),
+			cond: stmt.cond.as_ref(),
+			group: stmt.group.as_ref(),
+		}
+	}
+}
 
 pub(crate) struct QueryPlanner {
-	opt: Arc<Options>,
-	with: Option<Arc<With>>,
-	cond: Option<Arc<Cond>>,
-	order: Option<Arc<Orders>>,
 	/// There is one executor per table
 	executors: HashMap<String, QueryExecutor>,
 	requires_distinct: bool,
@@ -36,17 +52,8 @@ pub(crate) struct QueryPlanner {
 }
 
 impl QueryPlanner {
-	pub(crate) fn new(
-		opt: Arc<Options>,
-		with: Option<Arc<With>>,
-		cond: Option<Arc<Cond>>,
-		order: Option<Arc<Orders>>,
-	) -> Self {
+	pub(crate) fn new() -> Self {
 		Self {
-			opt,
-			with,
-			cond,
-			order,
 			executors: HashMap::default(),
 			requires_distinct: false,
 			fallbacks: vec![],
@@ -60,27 +67,22 @@ impl QueryPlanner {
 		&mut self,
 		stk: &mut Stk,
 		ctx: &Context,
+		opt: &Options,
 		t: Table,
+		params: &QueryPlannerParams<'_>,
 		it: &mut Iterator,
 	) -> Result<(), Error> {
 		let mut is_table_iterator = false;
-		let mut tree = Tree::build(
-			stk,
-			ctx,
-			&self.opt,
-			&t,
-			self.cond.as_ref().map(|w| w.as_ref()),
-			self.with.as_ref().map(|c| c.as_ref()),
-			self.order.as_ref().map(|o| o.as_ref()),
-		)
-		.await?;
+
+		let mut tree =
+			Tree::build(stk, ctx, opt, &t, params.cond, params.with, params.order).await?;
 
 		let is_knn = !tree.knn_expressions.is_empty();
 		let order = tree.index_map.order_limit.take();
 		let mut exe = InnerQueryExecutor::new(
 			stk,
 			ctx,
-			&self.opt,
+			opt,
 			&t,
 			tree.index_map,
 			tree.knn_expressions,
@@ -88,12 +90,7 @@ impl QueryPlanner {
 			tree.knn_condition,
 		)
 		.await?;
-		match PlanBuilder::build(
-			tree.root,
-			self.with.as_ref().map(|w| w.as_ref()),
-			tree.with_indexes,
-			order,
-		)? {
+		match PlanBuilder::build(tree.root, params, tree.with_indexes, order)? {
 			Plan::SingleIndex(exp, io) => {
 				if io.require_distinct() {
 					self.requires_distinct = true;
@@ -123,12 +120,12 @@ impl QueryPlanner {
 				let ir = exe.add_iterator(IteratorEntry::Range(rq.exps, ixn, rq.from, rq.to));
 				self.add(t.clone(), Some(ir), exe, it);
 			}
-			Plan::TableIterator(fallback) => {
-				if let Some(fallback) = fallback {
-					self.fallbacks.push(fallback);
+			Plan::TableIterator(reason, keys_only) => {
+				if let Some(reason) = reason {
+					self.fallbacks.push(reason);
 				}
 				self.add(t.clone(), None, exe, it);
-				it.ingest(Iterable::Table(t));
+				it.ingest(Iterable::Table(t, keys_only));
 				is_table_iterator = true;
 			}
 		}

core/src/idx/planner/plan.rs

@@ -1,6 +1,7 @@
 use crate::err::Error;
 use crate::idx::ft::MatchRef;
 use crate::idx::planner::tree::{GroupRef, IdiomCol, IdiomPosition, IndexRef, Node};
+use crate::idx::planner::QueryPlannerParams;
 use crate::sql::statements::DefineIndexStatement;
 use crate::sql::with::With;
 use crate::sql::{Array, Expression, Idiom, Number, Object};
@@ -31,13 +32,10 @@ pub(super) struct PlanBuilder {
 impl PlanBuilder {
 	pub(super) fn build(
 		root: Option<Node>,
-		with: Option<&With>,
+		params: &QueryPlannerParams,
 		with_indexes: Vec<IndexRef>,
 		order: Option<IndexOption>,
 	) -> Result<Plan, Error> {
-		if let Some(With::NoIndex) = with {
-			return Ok(Plan::TableIterator(Some("WITH NOINDEX".to_string())));
-		}
 		let mut b = PlanBuilder {
 			has_indexes: false,
 			non_range_indexes: Default::default(),
@@ -47,10 +45,18 @@ impl PlanBuilder {
 			all_and: true,
 			all_exp_with_index: true,
 		};
+
+		// If we only count and there are no conditions and no aggregations, then we can only scan keys
+		let keys_only = Self::is_keys_only(params);
+
+		if let Some(With::NoIndex) = params.with {
+			return Ok(Self::table_iterator(Some("WITH NOINDEX"), keys_only));
+		}
+
 		// Browse the AST and collect information
 		if let Some(root) = &root {
 			if let Err(e) = b.eval_node(root) {
-				return Ok(Plan::TableIterator(Some(e.to_string())));
+				return Ok(Self::table_iterator(Some(&e), keys_only));
 			}
 		}
 
@@ -84,7 +90,32 @@ impl PlanBuilder {
 			}
 			return Ok(Plan::MultiIndex(b.non_range_indexes, ranges));
 		}
-		Ok(Plan::TableIterator(None))
+		Ok(Self::table_iterator(None, keys_only))
+	}
+
+	fn is_keys_only(p: &QueryPlannerParams) -> bool {
+		if !p.fields.is_count_all_only() {
+			return false;
+		}
+		if p.cond.is_some() {
+			return false;
+		}
+		if let Some(g) = p.group {
+			if !g.is_empty() {
+				return false;
+			}
+		}
+		if let Some(p) = p.order {
+			if !p.is_empty() {
+				return false;
+			}
+		}
+		true
+	}
+
+	fn table_iterator(reason: Option<&str>, keys_only: bool) -> Plan {
+		let reason = reason.map(|s| s.to_string());
+		Plan::TableIterator(reason, keys_only)
 	}
 
 	// Check if we have an explicit list of index we can use
@@ -161,7 +192,7 @@ impl PlanBuilder {
 
 pub(super) enum Plan {
 	/// Table full scan
-	TableIterator(Option<String>),
+	TableIterator(Option<String>, bool),
 	/// Index scan filtered on records matching a given expression
 	SingleIndex(Option<Arc<Expression>>, IndexOption),
 	/// Union of filtered index scans

core/src/kvs/scanner.rs

@@ -11,9 +11,7 @@ use std::ops::Range;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
-type Output = Result<Vec<(Key, Val)>, Error>;
-
-pub(super) struct Scanner<'a> {
+pub(super) struct Scanner<'a, I> {
 	/// The store which started this range scan
 	store: &'a Transaction,
 	/// The number of keys to fetch at once
@@ -21,16 +19,17 @@ pub(super) struct Scanner<'a> {
 	// The key range for this range scan
 	range: Range<Key>,
 	// The results from the last range scan
-	results: VecDeque<(Key, Val)>,
+	results: VecDeque<I>,
+	#[allow(clippy::type_complexity)]
 	/// The currently running future to be polled
-	future: Option<Pin<Box<dyn Future<Output = Output> + 'a>>>,
+	future: Option<Pin<Box<dyn Future<Output = Result<Vec<I>, Error>> + 'a>>>,
 	/// Whether this stream should try to fetch more
 	exhausted: bool,
 	/// Version as timestamp, 0 means latest.
 	version: Option<u64>,
 }
 
-impl<'a> Scanner<'a> {
+impl<'a, I> Scanner<'a, I> {
 	pub fn new(
 		store: &'a Transaction,
 		batch: u32,
@@ -49,7 +48,7 @@ impl<'a> Scanner<'a> {
 	}
 }
 
-impl<'a> Stream for Scanner<'a> {
+impl<'a> Stream for Scanner<'a, (Key, Val)> {
 	type Item = Result<(Key, Val), Error>;
 	fn poll_next(
 		mut self: Pin<&mut Self>,
@@ -94,7 +93,9 @@ impl<'a> Stream for Scanner<'a> {
 								self.exhausted = true;
 							}
 							// Get the last element of the results
-							let last = v.last().unwrap();
+							let last = v.last().ok_or_else(|| {
+								Error::Unreachable("Last key/val can't be none".to_string())
+							})?;
 							// Start the next scan from the last result
 							self.range.start.clone_from(&last.0);
 							// Ensure we don't see the last result again
@@ -116,3 +117,70 @@ impl<'a> Stream for Scanner<'a> {
 		}
 	}
 }
+
+impl<'a> Stream for Scanner<'a, Key> {
+	type Item = Result<Key, Error>;
+	fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Result<Key, Error>>> {
+		// If we have results, return the first one
+		if let Some(v) = self.results.pop_front() {
+			return Poll::Ready(Some(Ok(v)));
+		}
+		// If we won't fetch more results then exit
+		if self.exhausted {
+			return Poll::Ready(None);
+		}
+		// Check if there is no pending future task
+		if self.future.is_none() {
+			// Set the max number of results to fetch
+			let num = std::cmp::min(*MAX_STREAM_BATCH_SIZE, self.batch);
+			// Clone the range to use when scanning
+			let range = self.range.clone();
+			// Prepare a future to scan for results
+			self.future = Some(Box::pin(self.store.keys(range, num)));
+		}
+		// Try to resolve the future
+		match self.future.as_mut().unwrap().poll_unpin(cx) {
+			// The future has now completed fully
+			Poll::Ready(result) => {
+				// Drop the completed asynchronous future
+				self.future = None;
+				// Check the result of the finished future
+				match result {
+					// The range was fetched successfully
+					Ok(v) => match v.is_empty() {
+						// There are no more results to stream
+						true => {
+							// Mark this stream as complete
+							Poll::Ready(None)
+						}
+						// There are results which need streaming
+						false => {
+							// We fetched the last elements in the range
+							if v.len() < self.batch as usize {
+								self.exhausted = true;
+							}
+							// Get the last element of the results
+							let last = v.last().ok_or_else(|| {
+								Error::Unreachable("Last key can't be none".to_string())
+							})?;
+							// Start the next scan from the last result
+							self.range.start.clone_from(last);
+							// Ensure we don't see the last result again
+							self.range.start.push(0xff);
+							// Store the fetched range results
+							self.results.extend(v);
+							// Remove the first result to return
+							let item = self.results.pop_front().unwrap();
+							// Return the first result
+							Poll::Ready(Some(Ok(item)))
+						}
+					},
+					// Return the received error
+					Err(error) => Poll::Ready(Some(Err(error))),
+				}
+			}
+			// The future has not yet completed
+			Poll::Pending => Poll::Pending,
+		}
+	}
+}

core/src/kvs/tx.rs

@@ -279,7 +279,7 @@ impl Transaction {
 	where
 		K: Into<Key> + Debug,
 	{
-		Scanner::new(
+		Scanner::<(Key, Val)>::new(
 			self,
 			*NORMAL_FETCH_SIZE,
 			Range {
@@ -290,6 +290,22 @@ impl Transaction {
 		)
 	}
 
+	#[instrument(level = "trace", target = "surrealdb::core::kvs::tx", skip_all)]
+	pub fn stream_keys<K>(&self, rng: Range<K>) -> impl Stream<Item = Result<Key, Error>> + '_
+	where
+		K: Into<Key> + Debug,
+	{
+		Scanner::<Key>::new(
+			self,
+			*NORMAL_FETCH_SIZE,
+			Range {
+				start: rng.start.into(),
+				end: rng.end.into(),
+			},
+			None,
+		)
+	}
+
 	// --------------------------------------------------
 	// Rollback methods
 	// --------------------------------------------------

core/src/sql/field.rs

@@ -41,6 +41,25 @@ impl Fields {
 			_ => None,
 		}
 	}
+
+	/// Check if the fields are only about counting
+	pub(crate) fn is_count_all_only(&self) -> bool {
+		let mut is_count_only = false;
+		for field in &self.0 {
+			if let Field::Single {
+				expr: Value::Function(func),
+				..
+			} = field
+			{
+				if func.is_count_all() {
+					is_count_only = true;
+					continue;
+				}
+			}
+			return false;
+		}
+		is_count_only
+	}
 }
 
 impl Deref for Fields {

core/src/sql/function.rs

@@ -180,6 +180,10 @@ impl Function {
 			_ => OptimisedAggregate::None,
 		}
 	}
+
+	pub(crate) fn is_count_all(&self) -> bool {
+		matches!(self, Self::Normal(f, p) if f == "count" && p.is_empty() )
+	}
 }
 
 impl Function {

core/src/sql/statements/select.rs

@@ -76,13 +76,6 @@ impl SelectStatement {
 		let version = self.version.as_ref().map(|v| v.to_u64());
 		let opt =
 			Arc::new(opt.new_with_futures(false).with_projections(true).with_version(version));
-		// Get a query planner
-		let mut planner = QueryPlanner::new(
-			opt.clone(),
-			self.with.as_ref().cloned().map(|w| w.into()),
-			self.cond.as_ref().cloned().map(|c| c.into()),
-			self.order.as_ref().cloned().map(|o| o.into()),
-		);
 		// Extract the limit
 		let limit = i.setup_limit(stk, ctx, &opt, &stm).await?;
 		// Used for ONLY: is the limit 1?
@@ -103,6 +96,9 @@ impl SelectStatement {
 			}
 			None => ctx.clone(),
 		};
+		// Get a query planner
+		let mut planner = QueryPlanner::new();
+		let params = self.into();
 		// Loop over the select targets
 		for w in self.what.0.iter() {
 			let v = w.compute(stk, &ctx, &opt, doc).await?;
@@ -111,7 +107,7 @@ impl SelectStatement {
 					if self.only && !limit_is_one_or_zero {
 						return Err(Error::SingleOnlyOutput);
 					}
-					planner.add_iterables(stk, &ctx, t, &mut i).await?;
+					planner.add_iterables(stk, &ctx, &opt, t, &params, &mut i).await?;
 				}
 				Value::Thing(v) => match &v.id {
 					Id::Range(r) => i.ingest(Iterable::TableRange(v.tb, *r.to_owned())),
@@ -141,7 +137,7 @@ impl SelectStatement {
 					for v in v {
 						match v {
 							Value::Table(t) => {
-								planner.add_iterables(stk, &ctx, t, &mut i).await?;
+								planner.add_iterables(stk, &ctx, &opt, t, &params, &mut i).await?;
 							}
 							Value::Thing(v) => i.ingest(Iterable::Thing(v)),
 							Value::Edges(v) => i.ingest(Iterable::Edges(*v)),

sdk/tests/group.rs

@@ -1,6 +1,7 @@
 mod parse;
 use parse::Parse;
 mod helpers;
+use crate::helpers::Test;
 use helpers::new_ds;
 use helpers::skip_ok;
 use surrealdb::dbs::Session;
@@ -734,3 +735,82 @@ async fn select_aggregate_mean_update() -> Result<(), Error> {
 
 	Ok(())
 }
+
+#[tokio::test]
+async fn select_count_group_all() -> Result<(), Error> {
+	let sql = r#"
+		CREATE table CONTENT { bar: "hello", foo: "Man"};
+		CREATE table CONTENT { bar: "hello", foo: "World"};
+		CREATE table CONTENT { bar: "world"};
+		SELECT COUNT() FROM table GROUP ALL EXPLAIN;
+		SELECT COUNT() FROM table GROUP ALL;
+		SELECT COUNT() FROM table EXPLAIN;
+		SELECT COUNT() FROM table;
+	"#;
+	let mut t = Test::new(sql).await?;
+	t.expect_size(7)?;
+	//
+	t.skip_ok(3)?;
+	//
+	t.expect_val(
+		r#"[
+				{
+					detail: {
+						table: 'table'
+					},
+					operation: 'Iterate Table Keys'
+				},
+				{
+					detail: {
+						idioms: {
+							count: [
+								'count'
+							]
+						},
+						type: 'Group'
+					},
+					operation: 'Collector'
+				}
+			]"#,
+	)?;
+	//
+	t.expect_val(
+		r#"[
+					{
+						count: 3
+					}
+				]"#,
+	)?;
+	//
+	t.expect_val(
+		r#"[
+					{
+						detail: {
+							table: 'table'
+						},
+						operation: 'Iterate Table Keys'
+					},
+					{
+						detail: {
+							type: 'Memory'
+						},
+						operation: 'Collector'
+					}
+				]"#,
+	)?;
+	//
+	t.expect_val(
+		r#"[
+				{
+					count: 1
+				},
+				{
+					count: 1
+				},
+				{
+					count: 1
+				}
+			]"#,
+	)?;
+	Ok(())
+}