建立或擴充讀取集區時，您必須等待與讀取集區相關聯的先前建立集區、縮減或擴充作業完成。這項限制適用於與相同主要執行個體相關聯的任何其他讀取集區。如要擴充與相同主要執行個體相關聯的多個讀取集區，請先等待與第一個讀取集區相關聯的擴充作業完成，再開始擴充下一個讀取集區。如果您發出並行要求，可能會收到下列錯誤：Operation failed because another operation was already in progress.。
[[["容易理解","easyToUnderstand","thumb-up"],["確實解決了我的問題","solvedMyProblem","thumb-up"],["其他","otherUp","thumb-up"]],[["難以理解","hardToUnderstand","thumb-down"],["資訊或程式碼範例有誤","incorrectInformationOrSampleCode","thumb-down"],["缺少我需要的資訊/範例","missingTheInformationSamplesINeed","thumb-down"],["翻譯問題","translationIssue","thumb-down"],["其他","otherDown","thumb-down"]],["上次更新時間：2025-09-04 (世界標準時間)。"],[],[],null,["# About read pools\n\n\u003cbr /\u003e\n\n[MySQL](/sql/docs/mysql/about-read-pools \"View this page for the MySQL database engine\") \\| PostgreSQL \\| SQL Server\n\n\u003cbr /\u003e\n\n|\n| **Preview**\n|\n|\n| This feature is subject to the \"Pre-GA Offerings Terms\" in the General Service Terms section\n| of the [Service Specific Terms](/terms/service-terms#1).\n|\n| You can process personal data for this feature as outlined in the\n| [Cloud Data Processing\n| Addendum](/terms/data-processing-addendum), subject to the obligations and restrictions described in the agreement under\n| which you access Google Cloud.\n|\n| Pre-GA features are available \"as is\" and might have limited support.\n|\n| For more information, see the\n| [launch stage descriptions](/products#product-launch-stages).\n\nCloud SQL read pools support load balancing for your large read workloads.\n\nWhat are read pools?\n--------------------\n\nA *read pool* is a collection of read replica instances used to distribute\nyour large read workloads. These workloads can be redirected from the primary\ninstance to the read pool to reduce load on the primary instance.\n\nEach read replica in the read pool is called a *read pool node*.\n\nYou can scale your read pool in several ways:\n\n- **Scale in or out**: scale load balancing capacity horizontally by modifying the number of read pool nodes in the read pool. Each read pool supports between 1 and 20 read pool nodes.\n- **Scale up or down**: scale load balancing capacity vertically by modifying the machine type associated with a read pool node. Once defined, configuration is uniformly applied across each read pool node in the read pool.\n\nWhen you modify read pool node settings such as storage, connectivity, or\ndatabase configuration flags, the changes are automatically applied uniformly\nacross each read pool node in the read pool.\n\nThe read pool is accessible through a *single read endpoint* with\nan immutable IP address. Connections made through the endpoint are\nautomatically redirected to one of the read pool nodes. When you want the\nread pool to scale in or scale out, applications that were previously\nconnected to this single read endpoint don't need to be reconfigured, even\nthough you can create new read pool nodes in the read pool or delete previous\nones.\n\nEach read pool node also has its own IP address. While not\nrecommended as an efficient approach for accessing your data, you can use\nthese IP addresses to troubleshoot individual read pool node performance.\n\nFor more information on how to retrieve the connection information for the\nread pool or the read pool nodes (either IP addresses or a connection string),\nsee\n[View read pool information](/sql/docs/postgres/create-read-pool#view-read-pool).\n\nThe following characteristics apply:\n\n- Read pool nodes of the read pool always reside in the same region, as specified by the user. Google Cloud alternates read pool node residency among all zones in the region.\n- A primary instance can have one or more read pools.\n- The following operations incur sub-second downtime:\n - Scaling out or in (adding or removing read pool nodes).\n - Scaling up or down (changing the machine type of the nodes in the pool).\n - Converting an existing zonal read replica to a read pool.\n- A read pool receives maintenance before its primary instance, similar to read replicas. Like read replicas, read pools receive maintenance during the primary instance's maintenance window.\n- Each read pool node has the same metrics available as a Cloud SQL read replica.\n- When using `gcloud` or the Google Cloud console to describe the details of a project, the read pool name is listed, individual read pool node names are not.\n\nLimitations\n-----------\n\nThe following limitations apply:\n\n- Read pools are only available for [Cloud SQL Enterprise Plus edition](/sql/docs/postgres/editions-intro) instances on the [new network architecture](/sql/docs/postgres/upgrade-cloud-sql-instance-new-network-architecture#check-single-instance). The primary instance associated with a read pool must also be a Cloud SQL Enterprise Plus edition instance.\n- Traffic is served from read pool nodes based on whether the database is healthy, but regardless of how high replication lag on that read pool node is. Traffic can be served from a lagging read pool node even if another read pool node is available that isn't lagging. A database is considered healthy if the database process is up and can answer queries, but there is no requirement on how fresh the data being served is.\n- No guarantee is made about a single logical session connecting to multiple read pool nodes in the read pool. It's possible for later requests in a session to connect to a read pool node that has a lower replication position (LSN) than the read pool node that served an earlier request, which can cause the state of the database to appear to go back in time.\n- The following types of updates aren't supported:\n - While read pools still receive Cloud SQL maintenance updates, you can't update your read pool to a new major database version.\n - Starting or stopping nodes of the read pool\n- In addition to operations that aren't supported on read replicas, the following operations aren't supported on read pools:\n - promote replica\n - restart\n - import\n - export\n - failover\n - re-encrypt\n - clone\n- The following features can't be used with a read pool:\n - Private Service Connect\n - SSL/TLS certificates with shared CA or customer-managed CA\n- A read pool can't replicate to another instance, for example, a cascading replica or another read pool.\n- A read pool must replicate directly from a primary instance. It can't be a cascading replica.\n- If you want to convert a regional read replica to a read pool, then you must first convert the regional read replica to a zonal read replica.\n- When creating or scaling a read pool, you must wait for previous create pool, scale in, or scale out operations associated with the read pool to finish. This restriction applies to any other read pool associated with the same primary instance. If you want to scale multiple read pools associated with the same primary instance, then you must wait for scaling operations associated with the first read pool to finish before you start scaling the next read pool. If you issue concurrent requests, then you might receive the following error: `Operation failed because another operation was already in progress.`.\n- Only a zonal replica located in the same region as the primary can be converted for use in a read pool.\n- You can't add or remove read pool nodes from the read pool while you're changing their machine type at the same time.\n- If your application must connect to a dedicated read replica---for example, because of secondary indexes present on a specific read replica---create a Cloud SQL read replica and use it instead.\n- You can't query specific users and databases associated with a read pool. Since Cloud SQL Studio relies on data provided by users and databases, Cloud SQL Studio isn't supported with read pools.\n\nWhat's next\n-----------\n\n- [Create and manage read pools](/sql/docs/postgres/create-read-pool)"]]
