複製作業會將交易從主要執行個體複製到一或多個唯讀備用資源。主要執行個體也稱為來源伺服器。來源伺服器可以是 Cloud SQL 主要執行個體，也可以是Google Cloud外部的伺服器，例如地端伺服器或在其他雲端執行的伺服器。如果來源伺服器不在 Google Cloud內，我們稱之為 Replication from an external server。
[[["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,["# Key terms\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\nTo use Cloud SQL effectively, you should understand some of the concepts on\nwhich it is built. This page provides an overview of key terms and concepts that\napply to Cloud SQL.\n\nFor an introduction to using Cloud SQL, see\n[Cloud SQL overview](/sql/docs/introduction).\n\nCloud SQL instance\n------------------\n\nA Cloud SQL instance corresponds to one virtual machine (VM).\nThe VM includes the database instance and accompanying software containers\nto keep the database instance up and running.\n\nDatabase instance\n-----------------\n\nA database instance is the set of software and files that operate the databases:\nMySQL, PostgreSQL or SQL Server.\n\nPublic and private IP\n---------------------\n\nIn Cloud SQL, public IP means that the instance is accessible through\nthe public internet. In contrast, instances using only private IP are not accessible through\nthe public internet, but are accessible through a\n[Virtual Private Cloud](https://cloud.google.com/vpc/docs/overview) (VPC).\nCloud SQL instances can have both a public and a private\nIP address.\n\nHigh availability\n-----------------\n\nCloud SQL instances using high availability (HA) provide greater\nreliability than non-HA instances.\n\nHA in Cloud SQL works by having two synchronized instances: a primary\ninstance and a standby instance. Each instance has exactly one VM. Each instance\nis in a different zone in the same region.\n\nFailover\n--------\n\nA failover is when Cloud SQL switches serving from the original primary\ninstance to the standby instance.\n\nAutofailover is a mechanism that automatically triggers failover when a\nCloud SQL instance didn't issue a heartbeat in the previous interval.\n\nStandby instances\n-----------------\n\nThe standby instance is used in high availability to replace the\nprimary instance when failover occurs. The standby instance doesn't appear in the\nGoogle Cloud console. When failover occurs, connections to the primary instance are\nautomatically transferred to the standby instance.\n\nClone\n-----\n\nWhen you clone a Cloud SQL instance, you create a new instance that is a\ncopy of the source instance, but is completely independent. After cloning is\ncomplete, changes to the source instance are not reflected in the clone, and\nchanges in the clone are not reflected in the source instance.\n\nReplication\n-----------\n\nReplication is the ability to create copies of a Cloud SQL instance or an\non-premises database, and offload work to the copies. The main reason for using\nreplication is to scale the use of data in a database without degrading\nperformance on the primary instance.\n\nRead replica\n------------\n\nThe read replica is an exact copy of the primary instance. Data and other\nchanges on the primary instance are updated in almost real time on the read\nreplica. Send your write transactions to the primary instance, and your read\nrequests to the read replica. The read replica processes queries, read requests,\nand analytics traffic, thus reducing the load on the primary instance.\n\nSource server\n-------------\n\nReplication copies transactions from a primary instance to one or more read\nreplicas. The primary instance is also called the source server. The source\nserver can be a Cloud SQL primary instance, or a server outside of\nGoogle Cloud, such as an on-premises server or a server running in a\ndifferent cloud. If the source server is outside of Google Cloud, we\ncall it `Replication from an external server`.\n\nCloud SQL Auth Proxy client\n---------------------------\n\nThe Cloud SQL Auth Proxy client is open source software maintained by Cloud SQL. It\nconnects to a companion process, the Cloud SQL Auth Proxy server, running on your\nCloud SQL instance. You run the Cloud SQL Auth Proxy client on your own servers. The\nCloud SQL Auth Proxy client can be used to establish a secure SSL/TLS connection to the\ndatabase instance, and/or to avoid having to open the firewall. Authentication\nis done through Identity and Access Management (IAM)."]]
