> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# delete Event

## Synopsis

A `delete` event occurs when operations remove documents from a collection, such as when a user or application executes the [`delete`](https://www.mongodb.com/docs/manual/reference/command/delete.md#mongodb-dbcommand-dbcmd.delete) command.

## Description

| Field | Type | Description |
| --- | --- | --- |
| `_id` | Document | A [BSON](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-BSON) object, which serves as an identifier for the change stream event. This value is used as the `resumeToken` for the `resumeAfter` parameter when resuming a change stream. The fields within the `_id` object depend on the MongoDB versions and, in some cases, the [feature compatibility version (FCV)](https://www.mongodb.com/docs/manual/reference/command/setfeaturecompatibilityversion.md#std-label-view-fcv) at the time of the change stream's opening or resumption. For an example of resuming a change stream by `resumeToken`, see [Resume a Change Stream.](https://www.mongodb.com/docs/manual/changestreams.md#std-label-change-stream-resume) |
| `clusterTime` | Timestamp | `clusterTime` is the timestamp from the oplog entry associated with the event. Due to [oplog size limits](https://www.mongodb.com/docs/manual/core/transactions-production-consideration.md#std-label-txn-oplog-size-limit), [multi-document transactions](https://www.mongodb.com/docs/manual/core/transactions.md#std-label-transactions) may create multiple oplog entries. In a transaction, change stream events staged in a given oplog entry share the same `clusterTime`. Events with the same `clusterTime` may not all relate to the same transaction. Some events don't relate to a transaction at all. Starting in MongoDB 8.0, this may be true for events on any deployment. In previous versions, this behavior was possible only for events on a sharded cluster. To identify events for a single transaction, you can use the combination of `lsid` and `txnNumber` in the change stream event document. **Changed in version 8.0** |
| `collectionUUID` | UUID | UUID (Universally Unique Identifier) identifying the collection where the change occurred. **New in version 6.0** The `collectionUUID` field is only included if the change stream is created with the `showExpandedEvents` field set to `true`. For details, see [showExpandedEvents.](https://www.mongodb.com/docs/manual/reference/change-events/#expanded-events) |
| `documentKey` | document | Document that contains the `_id` value of the document created or modified by the [CRUD](https://www.mongodb.com/docs/manual/crud.md#std-label-crud) operation. For sharded collections, this field also displays the shard key fields that are present in the document. MongoDB does not repeat the `_id` field if it is already a part of the shard key. To use this field as a query filter, see [Use documentKey as a Query Filter.](https://www.mongodb.com/docs/manual/changestreams.md#std-label-change-stream-document-key-filter) |
| `lsid` | document | The identifier for the session associated with the transaction. Only present if the operation is part of a [multi-document transaction.](https://www.mongodb.com/docs/manual/core/transactions.md) |
| `ns` | document | The namespace (database and or collection) affected by the event. |
| `ns.coll` | string | The name of the collection where the event occurred. |
| `ns.db` | string | The name of the database where the event occurred. |
| `operationDescription` | document | Additional information on the change operation. This document and its subfields only appears when the change stream uses [expanded events.](https://www.mongodb.com/docs/manual/reference/change-events.md#std-label-change-streams-expanded-events) **New in version 6.0** |
| `operationType` | string | The type of operation that the change notification reports. Returns a value of `delete` for these change events. |
| `txnNumber` | NumberLong | Together with the [lsid](https://www.mongodb.com/docs/manual/reference/change-events/update.md#std-label--idref--lsid), a number that helps uniquely identify a transction. Only present if the operation is part of a [multi-document transaction.](https://www.mongodb.com/docs/manual/core/transactions.md) |
| `wallTime` | [ISODate](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-ISODate) | The server date and time of the database operation. `wallTime` differs from `clusterTime` in that `clusterTime` is a timestamp taken from the oplog entry associated with the database operation event. **New in version 6.0** |

## Behavior

### Document Pre- and Post-Images

Starting in MongoDB 6.0, you see a `fullDocumentBeforeChange` document with the fields before the document was changed (or deleted) if you perform these steps:

1. Enable the new `changeStreamPreAndPostImages` field for a collection using [`db.createCollection()`](https://www.mongodb.com/docs/manual/reference/method/db.createcollection.md#mongodb-method-db.createCollection), [`create`](https://www.mongodb.com/docs/manual/reference/command/create.md#mongodb-dbcommand-dbcmd.create), or [`collMod`.](https://www.mongodb.com/docs/manual/reference/command/collmod.md#mongodb-dbcommand-dbcmd.collMod)

2. Set `fullDocumentBeforeChange` to `"required"` or `"whenAvailable"` in [`db.collection.watch()`.](https://www.mongodb.com/docs/manual/reference/method/db.collection.watch.md#mongodb-method-db.collection.watch)

Example `fullDocumentBeforeChange` document in the change stream output:

```json
"fullDocumentBeforeChange" : {
   "_id" : ObjectId("599af247bb69cd89961c986d"),
   "userName" : "alice123",
   "name" : "Alice Smith"
}
```

For complete examples with the change stream output, see [Change Streams with Document Pre- and Post-Images.](https://www.mongodb.com/docs/manual/reference/method/db.collection.watch.md#std-label-db.collection.watch-change-streams-pre-and-post-images-example)

Pre- and post-images are not available for a [change stream event](https://www.mongodb.com/docs/manual/reference/change-events.md#std-label-change-stream-output) if the images were:

- Not enabled on the collection at the time of a document update or delete operation.

- Removed after the pre- and post-image retention time set in `expireAfterSeconds`.

  - The following example sets `expireAfterSeconds` to `100` seconds on an entire cluster:

    ```javascript
    use admin
    db.runCommand( {
       setClusterParameter:
          { changeStreamOptions: {
             preAndPostImages: { expireAfterSeconds: 100 }
          } }
    } )
    ```

    **Note:**

    The [`setClusterParameter`](https://www.mongodb.com/docs/manual/reference/command/setclusterparameter.md#mongodb-dbcommand-dbcmd.setClusterParameter) command is not supported in MongoDB Atlas clusters. For information on Atlas support for all commands, see [Unsupported Commands in Atlas Clusters.](https://www.mongodb.com/docs/atlas/unsupported-commands.md#std-label-unsupported-commands)

  - The following example returns the current `changeStreamOptions` settings, including `expireAfterSeconds`:

    ```javascript
    db.adminCommand( { getClusterParameter: "changeStreamOptions" } )
    ```

  - Setting `expireAfterSeconds` to `off` uses the default retention policy: pre- and post-images are retained until the corresponding change stream events are removed from the [oplog.](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-oplog)

  - If a change stream event is removed from the oplog, then the corresponding pre- and post-images are also deleted regardless of the `expireAfterSeconds` pre- and post-image retention time.

Additional considerations:

- Enabling pre- and post-images consumes storage space and adds processing time. Only enable pre- and post-images if you need them.

- Limit the change stream event size to less than 16 mebibytes. To limit the event size, you can:

  - Limit the document size to 8 megabytes. You can request pre- and post-images simultaneously in the [change stream output](https://www.mongodb.com/docs/manual/reference/change-events.md#std-label-change-stream-output) if other change stream event fields like `updateDescription` are not large.

  - Request only post-images in the change stream output for documents up to 16 mebibytes if other change stream event fields like `updateDescription` are not large.

  - Request only pre-images in the change stream output for documents up to 16 mebibytes if:

    - document updates affect only a small fraction of the document structure or content, *and*

    - do not cause a `replace` change event. A `replace` event always includes the post-image.

- To request a pre-image, you set `fullDocumentBeforeChange` to `required` or `whenAvailable` in [`db.collection.watch()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.watch.md#mongodb-method-db.collection.watch). To request a post-image, you set `fullDocument` using the same method.

- Pre-images are written to the [`config.system.preimages`](https://www.mongodb.com/docs/manual/reference/system-collections.md#mongodb-data-config.system.preimages) collection.

  - The `config.system.preimages` collection may become large. To limit the collection size, you can set `expireAfterSeconds` time for the pre-images as shown earlier.

  - To monitor the size of `config.system.preimages`, connect to a shard node on a sharded cluster or a [`mongod`](https://www.mongodb.com/docs/manual/reference/program/mongod.md#mongodb-binary-bin.mongod) node on a replica set. Then, run the following commands:

    ```javascript
    use config
    db.system.preimages.totalSize()
    db.system.preimages.stats()
    ```

    **Note:**

    You must have the [`collStats`](https://www.mongodb.com/docs/manual/reference/privilege-actions.md#mongodb-authaction-collStats) privilege action on the `config.system.preimages` collection to run these commands.

    To run these commands on an MongoDB Atlas deployment, you must have the [`atlasAdmin`](https://www.mongodb.com/docs/manual/reference/built-in-roles.md#mongodb-atlasrole-atlasAdmin) role.

  - Pre-images are removed asynchronously by a background process.

**Important: Backward-Incompatible Feature**

Starting in MongoDB 6.0, if you are using document pre- and post-images for [change streams](https://www.mongodb.com/docs/manual/reference/change-events.md#std-label-change-stream-output), you must disable [changeStreamPreAndPostImages](https://www.mongodb.com/docs/manual/reference/command/collmod.md#std-label-collMod-change-stream-pre-and-post-images) for each collection using the [`collMod`](https://www.mongodb.com/docs/manual/reference/command/collmod.md#mongodb-dbcommand-dbcmd.collMod) command before you can downgrade to an earlier MongoDB version.

**See also:**

- For change stream events and output, see [Change Stream Events.](https://www.mongodb.com/docs/manual/reference/change-events.md#std-label-change-stream-output)

- To watch a collection for changes, see [`db.collection.watch()`.](https://www.mongodb.com/docs/manual/reference/method/db.collection.watch.md#mongodb-method-db.collection.watch)

- For complete examples with the change stream output, see [Change Streams with Document Pre- and Post-Images.](https://www.mongodb.com/docs/manual/reference/method/db.collection.watch.md#std-label-db.collection.watch-change-streams-pre-and-post-images-example)

## Example

The following example illustrates a `delete` event:

```json
{
   "_id": { <Resume Token> },
   "operationType": "delete",
   "clusterTime": <Timestamp>,
   "wallTime": <ISODate>,
   "ns": {
      "db": "engineering",
      "coll": "users"
   },
   "documentKey": {
      "_id": ObjectId("599af247bb69cd89961c986d")
   }
}
```

The `fullDocument` document is omitted as the document no longer exists at the time the change stream cursor sends the `delete` event to the client.