indexing docs

Author: AvijitkGupta

articles/cosmos-db/mongodb/vcore/TOC.yml

@@ -42,6 +42,10 @@
       href: high-availability.md
     - name: Cross-region replication
       href: cross-region-replication.md
+    - name: Indexing
+      href: indexing-basics.md
+    - name: Background indexing
+      href: background-indexing.md
     - name: Reliability
       href: /azure/reliability/reliability-cosmos-mongodb?toc=/azure/cosmos-db/mongodb/vcore/toc.json
     - name: Compute and storage

articles/cosmos-db/mongodb/vcore/background-indexing.md

@@ -0,0 +1,95 @@
+---
+title: Background Indexing
+titleSuffix: Background Indexing on Azure Cosmos DB for MongoDB vCore
+description: background indexing to enable non-blocking operation during index creation
+author: avijitkgupta
+ms.author: avijitkgupta
+ms.reviewer: gahllevy
+ms.service: cosmos-db
+ms.subservice: mongodb-vcore
+ms.topic: conceptual
+ms.date: 06/27/2024
+---
+
+# Background indexing (Preview)
+
+Background indexing is a technique that enables a database system to perform indexing operations on a collection without blocking other queries or updates. Azure CosmosDB for Mongo vcore accepts the indexing request and asynchronously performs it in background.
+
+Azure Cosmos DB for Mongo vcore allows indexing in background with property `enableIndexBuildBackground` set to true”. All indexes would be created in background except the unique indexes, post enabling the property.
+
+> [!NOTE]
+> If anticipated data size is large enough for a collection, then it might be sensible to create index on an empty collection.
+
+## Monitor index build
+
+We can learn about the progress of index build with command `currentOp`.
+
+```javascript
+db.currentOp("db_name":"<db_name>", "collection_name":"<collection_name>")
+```
+
+- `db_name` is an optional parameter.
+- `collection_name` is optional parameter.
+
+```json
+// Output for reviewing build status
+{
+inprog: [
+  {
+    shard: 'defaultShard',
+    active: true,
+    type: 'op',
+    opid: '10000003049:1701252500485346',
+    op_prefix: Long("10000003049"),
+    currentOpTime: ISODate("2024-06-24T10:08:20.000Z"),
+    secs_running: Long("2"),
+    command: {createIndexes: '' },
+    op: 'command',
+    waitingForLock: true
+  },
+  {
+    shard: 'defaultShard',
+    active: true,
+    type: 'op',
+    opid: '10000003050:1701252500499914',
+    op_prefix: Long("10000003050"),
+    currentOpTime: ISODate("2024-06-24T10:08:20.000Z"),
+    secs_running: Long("2"),
+    command: {
+      createIndexes: 'BRInventory-Multivendor', },
+      indexes: [
+        {
+          v:2,
+          key: {vendorItemId: 1, vendorId: 1, itemType: 1},
+          name: 'compound_idx'
+        }
+      ],
+      '$db': 'test'
+      op: 'command',
+      waitingForLock: false,
+      progress: {
+         blocks_done: Long("12616"),
+         blocks_done: Long("1276873"),
+         documents_d: Long("0"),
+         documents_to: Long("0")
+      },
+      msg: 'Building index.Progress 0.0098803875. Waiting on op_prefix: 10000000000.'
+    }
+  ],
+  ok: 1
+}
+```
+
+We can observe the build status with values depicted in table.
+
+| Status_Value |   Status    | Description |
+|--------------|-------------|-------------|
+|      1       | Queued      | Request is queued |
+|      2       | In progress | Request is picked |
+|      3       | Failed      | Request is already failed, 3 more retries will be attempted |
+|      4       | Skippable   | It should not be picked for processing. This should be deleted after 20 mins |
+
+## Limitations
+
+- Unique indexes cannot be created as background index. We recommend user to create unique index on empty collection first and then load the data into it.
+- Background index are performed in sequence over a single collection. Though background indexes on multiple collections can run in parallel.