Optimize joins to use index when possible

.changeset/sour-emus-count.md

@@ -0,0 +1,6 @@
+---
+"@tanstack/db-ivm": patch
+"@tanstack/db": patch
+---
+
+Optimize joins to use index on the join key when available.

packages/db-ivm/src/operators/index.ts

@@ -1,5 +1,6 @@
 export * from "./pipe.js"
 export * from "./map.js"
+export * from "./tap.js"
 export * from "./filter.js"
 export * from "./negate.js"
 export * from "./concat.js"

packages/db-ivm/src/operators/tap.ts

@@ -0,0 +1,53 @@
+import { DifferenceStreamWriter, LinearUnaryOperator } from "../graph.js"
+import { StreamBuilder } from "../d2.js"
+import type { IStreamBuilder, PipedOperator } from "../types.js"
+import type { DifferenceStreamReader } from "../graph.js"
+import type { MultiSet } from "../multiset.js"
+
+/**
+ * Operator that applies a function to each element in the input stream
+ */
+export class TapOperator<T> extends LinearUnaryOperator<T, T> {
+  #f: (data: T) => void
+
+  constructor(
+    id: number,
+    inputA: DifferenceStreamReader<T>,
+    output: DifferenceStreamWriter<T>,
+    f: (data: T) => void
+  ) {
+    super(id, inputA, output)
+    this.#f = f
+  }
+
+  inner(collection: MultiSet<T>): MultiSet<T> {
+    return collection.map((data) => {
+      this.#f(data)
+      return data
+    })
+  }
+}
+
+/**
+ * Invokes a function for each element in the input stream.
+ * This operator doesn't modify the stream and is used to perform side effects.
+ * @param f - The function to invoke on each element
+ * @returns The input stream
+ */
+export function tap<T>(f: (data: T) => void): PipedOperator<T, T> {
+  return (stream: IStreamBuilder<T>): IStreamBuilder<T> => {
+    const output = new StreamBuilder<T>(
+      stream.graph,
+      new DifferenceStreamWriter<T>()
+    )
+    const operator = new TapOperator<T>(
+      stream.graph.getNextOperatorId(),
+      stream.connectReader(),
+      output.writer,
+      f
+    )
+    stream.graph.addOperator(operator)
+    stream.graph.addStream(output.connectReader())
+    return output
+  }
+}

packages/db/src/collection.ts

@@ -1397,8 +1397,8 @@ export class CollectionImpl<
 
   /**
    * Creates an index on a collection for faster queries.
-   * Indexes significantly improve query performance by allowing binary search
-   * and range queries instead of full scans.
+   * Indexes significantly improve query performance by allowing constant time lookups
+   * and logarithmic time range queries instead of full scans.
    *
    * @template TResolver - The type of the index resolver (constructor or async loader)
    * @param indexCallback - Function that extracts the indexed value from each item

packages/db/src/errors.ts

@@ -377,6 +377,12 @@ export class UnknownFunctionError extends QueryCompilationError {
   }
 }
 
+export class JoinCollectionNotFoundError extends QueryCompilationError {
+  constructor(collectionId: string) {
+    super(`Collection "${collectionId}" not found during compilation of join`)
+  }
+}
+
 // JOIN Operation Errors
 export class JoinError extends TanStackDBError {
   constructor(message: string) {

packages/db/src/indexes/auto-index.ts

@@ -6,6 +6,55 @@ export interface AutoIndexConfig {
   autoIndex?: `off` | `eager`
 }
 
+function shouldAutoIndex(collection: CollectionImpl<any, any, any, any, any>) {
+  // Only proceed if auto-indexing is enabled
+  if (collection.config.autoIndex !== `eager`) {
+    return false
+  }
+
+  // Don't auto-index during sync operations
+  if (
+    collection.status === `loading` ||
+    collection.status === `initialCommit`
+  ) {
+    return false
+  }
+
+  return true
+}
+
+export function ensureIndexForField<
+  T extends Record<string, any>,
+  TKey extends string | number,
+>(
+  fieldName: string,
+  fieldPath: Array<string>,
+  collection: CollectionImpl<T, TKey, any, any, any>
+) {
+  if (!shouldAutoIndex(collection)) {
+    return
+  }
+
+  // Check if we already have an index for this field
+  const existingIndex = Array.from(collection.indexes.values()).find((index) =>
+    index.matchesField(fieldPath)
+  )
+
+  if (existingIndex) {
+    return // Index already exists
+  }
+
+  // Create a new index for this field using the collection's createIndex method
+  try {
+    collection.createIndex((row) => (row as any)[fieldName], {
+      name: `auto_${fieldName}`,
+      indexType: BTreeIndex,
+    })
+  } catch (error) {
+    console.warn(`Failed to create auto-index for field "${fieldName}":`, error)
+  }
+}
+
 /**
  * Analyzes a where expression and creates indexes for all simple operations on single fields
  */
@@ -16,44 +65,15 @@ export function ensureIndexForExpression<
   expression: BasicExpression,
   collection: CollectionImpl<T, TKey, any, any, any>
 ): void {
-  // Only proceed if auto-indexing is enabled
-  if (collection.config.autoIndex !== `eager`) {
-    return
-  }
-
-  // Don't auto-index during sync operations
-  if (
-    collection.status === `loading` ||
-    collection.status === `initialCommit`
-  ) {
+  if (!shouldAutoIndex(collection)) {
     return
   }
 
   // Extract all indexable expressions and create indexes for them
   const indexableExpressions = extractIndexableExpressions(expression)
 
   for (const { fieldName, fieldPath } of indexableExpressions) {
-    // Check if we already have an index for this field
-    const existingIndex = Array.from(collection.indexes.values()).find(
-      (index) => index.matchesField(fieldPath)
-    )
-
-    if (existingIndex) {
-      continue // Index already exists
-    }
-
-    // Create a new index for this field using the collection's createIndex method
-    try {
-      collection.createIndex((row) => (row as any)[fieldName], {
-        name: `auto_${fieldName}`,
-        indexType: BTreeIndex,
-      })
-    } catch (error) {
-      console.warn(
-        `Failed to create auto-index for field "${fieldName}":`,
-        error
-      )
-    }
+    ensureIndexForField(fieldName, fieldPath, collection)
   }
 }
 

packages/db/src/query/compiler/index.ts

@@ -7,6 +7,7 @@ import {
   LimitOffsetRequireOrderByError,
   UnsupportedFromTypeError,
 } from "../../errors.js"
+import { PropRef } from "../ir.js"
 import { compileExpression } from "./evaluators.js"
 import { processJoins } from "./joins.js"
 import { processGroupBy } from "./group-by.js"
@@ -18,6 +19,8 @@ import type {
   QueryIR,
   QueryRef,
 } from "../ir.js"
+import type { LazyCollectionCallbacks } from "./joins.js"
+import type { Collection } from "../../collection.js"
 import type {
   KeyedStream,
   NamespacedAndKeyedStream,
@@ -29,6 +32,8 @@ import type { QueryCache, QueryMapping } from "./types.js"
  * Result of query compilation including both the pipeline and collection-specific WHERE clauses
  */
 export interface CompilationResult {
+  /** The ID of the main collection */
+  collectionId: string
   /** The compiled query pipeline */
   pipeline: ResultStream
   /** Map of collection aliases to their WHERE clauses for index optimization */
@@ -46,6 +51,9 @@ export interface CompilationResult {
 export function compileQuery(
   rawQuery: QueryIR,
   inputs: Record<string, KeyedStream>,
+  collections: Record<string, Collection<any, any, any, any, any>>,
+  callbacks: Record<string, LazyCollectionCallbacks>,
+  lazyCollections: Set<string>,
   cache: QueryCache = new WeakMap(),
   queryMapping: QueryMapping = new WeakMap()
 ): CompilationResult {
@@ -70,9 +78,16 @@ export function compileQuery(
   const tables: Record<string, KeyedStream> = {}
 
   // Process the FROM clause to get the main table
-  const { alias: mainTableAlias, input: mainInput } = processFrom(
+  const {
+    alias: mainTableAlias,
+    input: mainInput,
+    collectionId: mainCollectionId,
+  } = processFrom(
     query.from,
     allInputs,
+    collections,
+    callbacks,
+    lazyCollections,
     cache,
     queryMapping
   )
@@ -96,10 +111,15 @@ export function compileQuery(
       pipeline,
       query.join,
       tables,
+      mainCollectionId,
       mainTableAlias,
       allInputs,
       cache,
-      queryMapping
+      queryMapping,
+      collections,
+      callbacks,
+      lazyCollections,
+      rawQuery
     )
   }
 
@@ -249,6 +269,7 @@ export function compileQuery(
     const result = resultPipeline
     // Cache the result before returning (use original query as key)
     const compilationResult = {
+      collectionId: mainCollectionId,
       pipeline: result,
       collectionWhereClauses,
     }
@@ -275,6 +296,7 @@ export function compileQuery(
   const result = resultPipeline
   // Cache the result before returning (use original query as key)
   const compilationResult = {
+    collectionId: mainCollectionId,
     pipeline: result,
     collectionWhereClauses,
   }
@@ -289,16 +311,19 @@ export function compileQuery(
 function processFrom(
   from: CollectionRef | QueryRef,
   allInputs: Record<string, KeyedStream>,
+  collections: Record<string, Collection>,
+  callbacks: Record<string, LazyCollectionCallbacks>,
+  lazyCollections: Set<string>,
   cache: QueryCache,
   queryMapping: QueryMapping
-): { alias: string; input: KeyedStream } {
+): { alias: string; input: KeyedStream; collectionId: string } {
   switch (from.type) {
     case `collectionRef`: {
       const input = allInputs[from.collection.id]
       if (!input) {
         throw new CollectionInputNotFoundError(from.collection.id)
       }
-      return { alias: from.alias, input }
+      return { alias: from.alias, input, collectionId: from.collection.id }
     }
     case `queryRef`: {
       // Find the original query for caching purposes
@@ -308,6 +333,9 @@ function processFrom(
       const subQueryResult = compileQuery(
         originalQuery,
         allInputs,
+        collections,
+        callbacks,
+        lazyCollections,
         cache,
         queryMapping
       )
@@ -324,7 +352,11 @@ function processFrom(
         })
       )
 
-      return { alias: from.alias, input: extractedInput }
+      return {
+        alias: from.alias,
+        input: extractedInput,
+        collectionId: subQueryResult.collectionId,
+      }
     }
     default:
       throw new UnsupportedFromTypeError((from as any).type)
@@ -380,3 +412,69 @@ function mapNestedQueries(
     }
   }
 }
+
+function getRefFromAlias(
+  query: QueryIR,
+  alias: string
+): CollectionRef | QueryRef | void {
+  if (query.from.alias === alias) {
+    return query.from
+  }
+
+  for (const join of query.join || []) {
+    if (join.from.alias === alias) {
+      return join.from
+    }
+  }
+}
+
+/**
+ * Follows the given reference in a query
+ * until its finds the root field the reference points to.
+ * @returns The collection, its alias, and the path to the root field in this collection
+ */
+export function followRef(
+  query: QueryIR,
+  ref: PropRef<any>,
+  collection: Collection
+): { collection: Collection; path: Array<string> } | void {
+  if (ref.path.length === 0) {
+    return
+  }
+
+  if (ref.path.length === 1) {
+    // This field should be part of this collection
+    const field = ref.path[0]!
+    // is it part of the select clause?
+    if (query.select) {
+      const selectedField = query.select[field]
+      if (selectedField && selectedField.type === `ref`) {
+        return followRef(query, selectedField, collection)
+      }
+    }
+
+    // Either this field is not part of the select clause
+    // and thus it must be part of the collection itself
+    // or it is part of the select but is not a reference
+    // so we can stop here and don't have to follow it
+    return { collection, path: [field] }
+  }
+
+  if (ref.path.length > 1) {
+    // This is a nested field
+    const [alias, ...rest] = ref.path
+    const aliasRef = getRefFromAlias(query, alias!)
+    if (!aliasRef) {
+      return
+    }
+
+    if (aliasRef.type === `queryRef`) {
+      return followRef(aliasRef.query, new PropRef(rest), collection)
+    } else {
+      // This is a reference to a collection
+      // we can't follow it further
+      // so the field must be on the collection itself
+      return { collection: aliasRef.collection, path: rest }
+    }
+  }
+}