[[["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)。"],[[["\u003cp\u003eThis API supports first-generation runtimes and is relevant when upgrading to corresponding second-generation runtimes, with a migration guide available for those updating to App Engine Go 1.12+.\u003c/p\u003e\n"],["\u003cp\u003eDatastore queries have two consistency levels: strongly consistent queries, which provide the freshest results but may take longer, and eventually consistent queries, which are faster but may return stale results.\u003c/p\u003e\n"],["\u003cp\u003eAncestor queries are strongly consistent by default but can be made eventually consistent, whereas non-ancestor queries are always eventually consistent.\u003c/p\u003e\n"],["\u003cp\u003eFetching an entity by key is a strongly consistent operation.\u003c/p\u003e\n"],["\u003cp\u003eFurther learning resources are available on specifying query returns, restrictions, cursors, and the basic syntax of Datastore queries.\u003c/p\u003e\n"]]],[],null,["# Data Consistency in Datastore Queries\n\n| This API is supported for first-generation runtimes and can be used when [upgrading to corresponding second-generation runtimes](/appengine/docs/standard/\n| go\n| /services/access). If you are updating to the App Engine Go 1.12+ runtime, refer to the [migration guide](/appengine/migration-center/standard/migrate-to-second-gen/go-differences) to learn about your migration options for legacy bundled services.\n\nData consistency levels\n-----------------------\n\nDatastore queries can deliver their results at either of two consistency\nlevels:\n\n- [*Strongly consistent*](https://en.wikipedia.org/wiki/Strong_consistency) queries guarantee the freshest results, but may take longer to complete.\n- [*Eventually consistent*](https://en.wikipedia.org/wiki/Eventual_consistency) queries generally run faster, but may occasionally return stale results.\n\nIn an eventually consistent query, the indexes used to gather the results are also accessed with eventual consistency. Consequently, such queries may sometimes return entities that no longer match the original query criteria, while strongly consistent queries are always transactionally consistent.\n\nDatastore query data consistency\n--------------------------------\n\nQueries return their results with different levels of consistency guarantee, depending on the nature of the query:\n\n- [Ancestor queries](/appengine/docs/legacy/standard/go111/datastore/queries#ancestor_queries) (those within an [entity group](./#Go_Ancestor_paths) ) are strongly consistent by default, but can instead be made eventually consistent by setting the Datastore read policy (see below).\n- Non-ancestor queries are always eventually consistent.\n\nFetching an entity by key, which is also called \"lookup by key\", is strongly\nconsistent.\n\nWhat's next?\n------------\n\n- [Learn how to specify what a query returns and further control query results](/appengine/docs/legacy/standard/go111/datastore/retrieving-query-results).\n- Learn the [common restrictions](/appengine/docs/legacy/standard/go111/datastore/query-restrictions) for queries on Datastore.\n- Learn about [query cursors](/appengine/docs/legacy/standard/go111/datastore/query-cursors), which allow an application to retrieve a query's results in convenient batches.\n- Learn the [basic syntax and structure of queries](/appengine/docs/legacy/standard/go111/datastore/queries) for Datastore."]]
