fix(db): avoid full row origin snapshots

.changeset/quiet-row-origins.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/db': patch
+---
+
+Avoid full row origin snapshots during incremental collection updates and make bulk mutation merging linear.

packages/db/src/collection/state.ts

@@ -226,6 +226,21 @@ export class CollectionStateManager<
     })
   }
 
+  private snapshotRowOriginsForKeys(
+    keys: Iterable<TKey>,
+  ): Map<TKey, VirtualOrigin> {
+    const rowOrigins = new Map<TKey, VirtualOrigin>()
+
+    for (const key of keys) {
+      const origin = this.rowOrigins.get(key)
+      if (origin !== undefined) {
+        rowOrigins.set(key, origin)
+      }
+    }
+
+    return rowOrigins
+  }
+
   private enrichWithVirtualPropsSnapshot(
     row: TOutput,
     virtualProps: VirtualRowProps<TKey>,
@@ -476,7 +491,7 @@ export class CollectionStateManager<
 
     const previousState = new Map(this.optimisticUpserts)
     const previousDeletes = new Set(this.optimisticDeletes)
-    const previousRowOrigins = new Map(this.rowOrigins)
+    const previousRowOrigins = this.rowOrigins
 
     // Update pending optimistic state for completed/failed transactions
     for (const transaction of this.transactions.values()) {
@@ -857,10 +872,6 @@ export class CollectionStateManager<
       // Set flag to prevent redundant optimistic state recalculations
       this.isCommittingSyncTransactions = true
 
-      const previousRowOrigins = new Map(this.rowOrigins)
-      const previousOptimisticUpserts = new Map(this.optimisticUpserts)
-      const previousOptimisticDeletes = new Set(this.optimisticDeletes)
-
       // Get the optimistic snapshot from the truncate transaction (captured when truncate() was called)
       const truncateOptimisticSnapshot = hasTruncateSync
         ? committedSyncedTransactions.find((t) => t.truncate)
@@ -880,6 +891,18 @@ export class CollectionStateManager<
         }
       }
 
+      const virtualSnapshotKeys = new Set(changedKeys)
+      for (const key of this.pendingOptimisticDirectUpserts) {
+        virtualSnapshotKeys.add(key)
+      }
+      for (const key of this.pendingOptimisticDirectDeletes) {
+        virtualSnapshotKeys.add(key)
+      }
+      const previousRowOrigins =
+        this.snapshotRowOriginsForKeys(virtualSnapshotKeys)
+      const previousOptimisticUpserts = new Map(this.optimisticUpserts)
+      const previousOptimisticDeletes = new Set(this.optimisticDeletes)
+
       // Use pre-captured state if available (from optimistic scenarios),
       // otherwise capture current state (for pure sync scenarios)
       let currentVisibleState = this.preSyncVisibleState

packages/db/src/transactions.ts

@@ -334,27 +334,39 @@ class Transaction<T extends object = Record<string, unknown>> {
    * @param mutations - Array of new mutations to apply
    */
   applyMutations(mutations: Array<PendingMutation<any>>): void {
+    // Merge via a globalKey-keyed map rather than a findIndex scan per
+    // mutation, which is O(n²) for bulk operations (e.g. inserting many rows
+    // in one call). Map preserves insertion order, matching the previous
+    // replace-in-place / remove / append semantics.
+    const merged = new Map<string, PendingMutation<any>>()
+    for (const mutation of this.mutations) {
+      merged.set(mutation.globalKey, mutation)
+    }
+
     for (const newMutation of mutations) {
-      const existingIndex = this.mutations.findIndex(
-        (m) => m.globalKey === newMutation.globalKey,
-      )
+      const existingMutation = merged.get(newMutation.globalKey)
 
-      if (existingIndex >= 0) {
-        const existingMutation = this.mutations[existingIndex]!
+      if (existingMutation) {
         const mergeResult = mergePendingMutations(existingMutation, newMutation)
 
         if (mergeResult === null) {
           // Remove the mutation (e.g., delete after insert cancels both)
-          this.mutations.splice(existingIndex, 1)
+          merged.delete(newMutation.globalKey)
         } else {
           // Replace with merged mutation
-          this.mutations[existingIndex] = mergeResult
+          merged.set(newMutation.globalKey, mergeResult)
         }
       } else {
         // Insert new mutation
-        this.mutations.push(newMutation)
+        merged.set(newMutation.globalKey, newMutation)
       }
     }
+
+    // Rebuild in place to preserve the array's identity for external holders
+    this.mutations.length = 0
+    for (const mutation of merged.values()) {
+      this.mutations.push(mutation)
+    }
   }
 
   /**