Docs Home → MongoDB Manual

Hidden Indexes隐藏索引

On this page

New in version 4.4.

Hidden indexes are not visible to the query planner and cannot be used to support a query.隐藏索引对查询计划器不可见，不能用于支持查询。

By hiding an index from the planner, users can evaluate the potential impact of dropping an index without actually dropping the index. 通过向计划器隐藏索引，用户可以在不实际删除索引的情况下评估删除索引的潜在影响。If the impact is negative, the user can unhide the index instead of having to recreate a dropped index.如果影响是负面的，用户可以取消隐藏索引，而不必重新创建已删除的索引。

Behavior行为

Apart from being hidden from the planner, hidden indexes behave like unhidden indexes. 除了对计划器隐藏之外，隐藏索引的行为与未隐藏索引类似。For example:例如：

  • If a hidden index is a unique index, the index still applies its unique constraint to the documents.如果隐藏索引是唯一索引，则该索引仍将其唯一约束应用于文档。

  • If a hidden index is a TTL index, the index still expires documents.如果隐藏索引是TTL索引，则该索引仍然会使文档过期。

  • Hidden indexes are included in listIndexes and db.collection.getIndexes() results.listIndexes和db.collection.getIndexes()结果中包含隐藏索引。

  • Hidden indexes are updated upon write operations to the collection and continue to consume disk space and memory. 隐藏索引会在对集合执行写入操作时更新，并继续消耗磁盘空间和内存。As such, they are included in various statistics operations, such as db.collection.stats() and $indexStats.因此，它们包含在各种统计操作中，例如db.collection.stats()和$indexStats。

  • Hiding an unhidden index or unhiding a hidden index resets its $indexStats. 隐藏未隐藏的索引或取消隐藏隐藏的索引会重置其$indexStats。Hiding an already hidden index or unhiding an already unhidden index does not reset the $indexStats.隐藏已隐藏的索引或取消隐藏已取消隐藏的索引不会重置$indexStats。

Restrictions限制

Examples实例

Create a Hidden Index创建隐藏索引

To create a hidden index, use the db.collection.createIndex() method with the hidden option set to true.要创建hidden索引，请使用db.collection.createIndex()方法，并将hidden选项设置为true。

Note

To use the hidden option with db.collection.createIndex(), you must have featureCompatibilityVersion set to 4.4 or greater. 要在db.collection.createIndex()中使用hidden选项，必须将featureCompatibilityVersion设置为4.4或更高版本。However, once hidden, the index remains hidden even with featureCompatibilityVersion set to 4.2 on MongoDB 4.4 binaries.然而，一旦隐藏，即使在MongoDB 4.4二进制文件中将featureCompatibilityVersion设置为4.2，索引也会保持隐藏状态。

For example, the following operation creates a hidden ascending index on the borough field:例如，以下操作在borough字段上创建一个隐藏的升序索引：

db.addresses.createIndex(
   { borough: 1 },
   { hidden: true }
);

To verify, run db.collection.getIndexes() on the addresses collection:若要验证，请对addresses集合运行db.collection.getIndexes()：

db.addresses.getIndexes()

The operation returns the following information:该操作返回以下信息：

[
   {
      "v" : 2,
      "key" : {
         "_id" : 1
      },
      "name" : "_id_"
   },
   {
      "v" : 2,
      "key" : {
         "borough" : 1
      },
      "name" : "borough_1",
      "hidden" : true
   }
]

The index option hidden is only returned if the value is true.只有当值为true时，才会返回hidden的索引选项。

Hide an Existing Index隐藏现有索引

Note

To hide an existing index, you can use the collMod command or mongosh helper db.collection.hideIndex().要隐藏现有索引，可以使用collModd命令或mongosh助手db.collection.hideIndex()。

For example, create an index without hiding:例如，创建一个不隐藏的索引：

db.restaurants.createIndex( { borough: 1, ratings: 1 } );

To hide the index, you can specify either:要隐藏索引，可以指定以下任一项：

  • the index key specification document to the db.collection.hideIndex() method:db.collection.hideIndex()方法的索引键规范文档：

    db.restaurants.hideIndex( { borough: 1, ratings: 1 } ); // Specify the index key specification document指定索引键规范文档

  • the index name to the db.collection.hideIndex() method:

    db.restaurants.hideIndex( "borough_1_ratings_1" );  // Specify the index name指定索引名称

To verify, run db.collection.getIndexes() on the restaurants collection:要进行验证，请在restaurants集合上运行db.collection.getIndexes()：

db.restaurants.getIndexes()

The operation returns the following information:该操作返回以下信息：

[
   {
      "v" : 2,
      "key" : {
         "_id" : 1
      },
      "name" : "_id_"
   },
   {
      "v" : 2,
      "key" : {
         "borough" : 1,
         "ratings" : 1
      },
      "name" : "borough_1_ratings_1",
      "hidden" : true
   }
]

The index option hidden is only returned if the value is true.只有当值为true时，才会返回hidden的索引选项。

Unhide an Existing Index取消隐藏现有索引

To unhide a hidden index, you can use the collMod command or mongosh helper db.collection.unhideIndex(). 要取消隐藏索引，可以使用collMod命令或mongosh助手db.collection.unhideIndex()。You can specify either:您可以指定以下任一项：

To verify, run db.collection.getIndexes() on the restaurants collection:要进行验证，请在restaurants集合上运行db.collection.getIndexes()：

db.restaurants.getIndexes()

The operation returns the following information:该操作返回以下信息：

[
   {
      "v" : 2,
      "key" : {
         "_id" : 1
      },
      "name" : "_id_"
   },
   {
      "v" : 2,
      "key" : {
         "borough" : 1,
         "ratings" : 1
      },
      "name" : "borough_1_ratings_1"
   }
]

The index option hidden no longer appears as part of the borough_1_ratings_1 index since the field is only returned if the value is true.hidden的索引选项不再显示为borough_1_ratings_1索引的一部分，因为只有当值为true时才会返回该字段。

Because indexes are fully maintained while hidden, the index is immediately available for use once unhidden.因为索引在隐藏时是完全维护的，所以一旦取消隐藏，索引就可以立即使用。