[Durable Objects] Including that writing to indexes and virtual tables takes up rows written (#18450)

* Adding a note to say writing to indexes count as additional rows.

* Adding virtual tables into the note.

Author: Oxyjun

src/content/docs/durable-objects/api/sql-storage.mdx

@@ -37,6 +37,12 @@ export class MyDurableObject extends DurableObject {
 SQL API methods accessed with `ctx.storage.sql` are only allowed on [Durable Object classes with SQLite storage backend](/durable-objects/reference/durable-objects-migrations/#enable-sqlite-storage-backend-on-new-durable-object-class-migration) and will return an error if called on Durable Object classes with a key-value storage backend.
 :::
 
+:::note[Writing to indexes or virtual tables]
+When writing data, every index counts as an additional row. However, indexes may be beneficial for read-heavy use cases. Refer to [Index for SQLite Durable Objects](/durable-objects/best-practices/access-durable-objects-storage/#index-for-sqlite-durable-objects).
+
+Writing data to [SQLite virtual tables](https://www.sqlite.org/vtab.html) also counts towards rows written.
+:::
+
 Specifically for Durable Object classes with SQLite storage backend, KV operations which were previously asynchronous (for example, [`get`](/durable-objects/api/storage-api/#get), [`put`](/durable-objects/api/storage-api/#put), [`delete`](/durable-objects/api/storage-api/#delete), [`deleteAll`](/durable-objects/api/storage-api/#deleteall), [`list`](/durable-objects/api/storage-api/#list)) are synchronous, even though they return promises. These methods will have completed their operations before they return the promise.
 
 ## Methods

src/content/docs/durable-objects/best-practices/access-durable-objects-storage.mdx

@@ -78,6 +78,10 @@ new_sqlite_classes = ["MyDurableObject"] # Array of new classes
 
 <Render file="durable-objects-vs-d1" />
 
+## Index for SQLite Durable Objects
+
+Creating indexes for your most queried tables and filtered columns reduces how much data is scanned and improves query performance at the same time. If you have a read-heavy workload (most common), this can be particularly advantageous. Writing to columns referenced in an index will add at least one (1) additional row written to account for updating the index, but this is typically offset by the reduction in rows read due to the benefits of an index.
+
 ## Related resources
 
 * [Zero-latency SQLite storage in every Durable Object blog post](https://blog.cloudflare.com/sqlite-in-durable-objects)