{"Entry":{"collection":"guc","key":"transaction_read_only","name":"transaction_read_only","aliases":[],"metadata":{"baseline":false,"boot_human":"Not specified","boot_val":null,"category":"Client Connection Defaults / Statement Behavior","category_zh":"","changed_in":[],"changes":[{"documentation_changed":false,"fields":{},"from":"8.4","status":"added","to":"9.0"},{"documentation_changed":true,"fields":{},"from":"9.5","status":"changed","to":"9.6"}],"content_hash":"533b3e60abd302cdb811d063c5934dd81cfd0d94119798af48baf3bf998cc4e8","context":"","default_changed_in":[],"default_history":[{"from":"9.0","to":"19","value":"off"}],"editorial":{"advice":{"olap":"For reporting, consider a read-only transaction and an isolation choice that matches snapshot requirements; use deferrability only with read-only serializable work.","oltp":"Choose transaction_read_only for correctness semantics first. Keep the common OLTP path explicit, then override only transactions whose consistency contract justifies different blocking or retry behavior.","small":"Do not change transaction_read_only as a generic speed tweak. Higher isolation or long snapshots can amplify contention and vacuum pressure on a small node."},"mechanism":["transaction_read_only sets the current transaction's read-only status. It reflects the current transaction, begins from default_transaction_read_only, and must be set before operations that conflict with read-only mode.","transaction_read_only is session-settable but represents the current transaction; PostgreSQL restricts changes after the transaction has acquired a snapshot or performed conflicting work.","The default_* variables seed the corresponding transaction_* state. Isolation, read-only status, deferrability, retries, and snapshot lifetime must be designed together."],"pitfalls":["Changing transaction_read_only in one session and assuming role defaults, database defaults, or other pooled sessions changed with it.","Changing transaction semantics as a performance experiment and silently weakening an application's consistency contract.","Letting a pooled session retain transaction-related state because checkout or rollback/reset handling is incomplete.","Changing transaction_read_only globally without a rollback plan and a client or operational compatibility test."],"references":[{"title":"PostgreSQL 19 Beta 4: transaction_read_only","url":"https://www.postgresql.org/docs/19/runtime-config-client.html#GUC-TRANSACTION-READ-ONLY"},{"title":"PostgreSQL 19 release notes","url":"https://www.postgresql.org/docs/19/release-19.html"}],"related":["default_transaction_isolation","transaction_isolation","default_transaction_read_only","default_transaction_deferrable","transaction_deferrable"],"summary":"transaction_read_only is the PostgreSQL setting that defines the current transaction's read-only status."},"enumvals":[],"first_version":"9.0","group":"Client Connection Defaults","group_slug":"client","imported_at":"2026-09-27T17:57:32.23402+08:00","intro_commit":{},"key":"transaction_read_only","last_version":"20","max_val":"","min_val":"","name":"transaction_read_only","position":436,"present_in":["9.0","9.1","9.2","9.3","9.4","9.5","9.6","10","11","12","13","14","15","16","17","18","19","20"],"short_desc":"This parameter reflects the current transaction's read-only status.","short_desc_zh":"","source_rev":"english-manuals:bfd568fc8a9d915c53797166602b57c3df1db3a78725c09edbcea1df653f6dcf","unit":"","vartype":"bool"}},"Definition":{"Collection":"guc","Key":"transaction_read_only","SourceDatabase":"center","Version":"18","SourceTable":"guc","SourceKey":"transaction_read_only","SourceRevision":"english-manuals:bfd568fc8a9d915c53797166602b57c3df1db3a78725c09edbcea1df653f6dcf","Facts":{"boot_val":"off","category":"Client Connection Defaults / Statement Behavior","context":"user","description":"This parameter reflects the current transaction's read-only status. At the beginning of each transaction, it is set to the current value of default_transaction_read_only. Any subsequent attempt to change it is equivalent to a SET TRANSACTION command.","doc":{"anchor":"GUC-TRANSACTION-READ-ONLY","file":"runtime-config-client.html","lang":"en","sha256":"6be6cc70f29eca4695dc43b2b2b94c75b7e0eaaa2c00273d7a98488917a7edb7","slug":"18"},"documented":true,"enumvals":null,"extra_desc":null,"lang":"en","max_val":null,"metadata_version":"18","min_val":null,"name":"transaction_read_only","short_desc":"Sets the current transaction's read-only status.","source":"pg-settings-source-snapshot","unit":null,"vartype":"bool"},"ManualEvidence":{"doc":{"anchor":"GUC-TRANSACTION-READ-ONLY","file":"runtime-config-client.html","lang":"en","sha256":"6be6cc70f29eca4695dc43b2b2b94c75b7e0eaaa2c00273d7a98488917a7edb7","slug":"18"}},"MeasuredEvidence":{"metadata_version":"18"}},"Text":{"Collection":"guc","Key":"transaction_read_only","SourceDatabase":"pgweb","Version":"18","Locale":"zh-Hans","Title":"transaction_read_only","Summary":"","BodyHTML":"\u003cp\u003e此参数反映当前事务的只读状态。在每个事务的开始，它被设置为\u003ca href=\"/docs/18/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-READ-ONLY\" rel=\"nofollow\"\u003edefault_transaction_read_only\u003c/a\u003e的当前值。任何后续更改它的尝试都等同于\u003ca href=\"/docs/18/sql-set-transaction.html\" title=\"SET TRANSACTION\" rel=\"nofollow\"\u003e\u003cspan\u003eSET TRANSACTION\u003c/span\u003e\u003c/a\u003e命令。\u003c/p\u003e","SourceRevision":"2026-09-11@29c86d9","ContentHash":"8bad35ef36745dbc8b4cd7bc8756d7de2692a833c20c722a6c21148658be816a","Payload":{"carried_from":"","carry_reason":"","doc_html":"\u003cp\u003e此参数反映当前事务的只读状态。在每个事务的开始，它被设置为\u003ca href=\"/docs/18/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-READ-ONLY\"\u003edefault_transaction_read_only\u003c/a\u003e的当前值。任何后续更改它的尝试都等同于\u003ca href=\"/docs/18/sql-set-transaction.html\" title=\"SET TRANSACTION\"\u003e\u003cspan class=\"refentrytitle\"\u003eSET TRANSACTION\u003c/span\u003e\u003c/a\u003e命令。\u003c/p\u003e","doc_same_as":""}},"RequestedLocale":"zh-Hans","Fallback":false,"Versions":["10","11","12","13","14","15","16","17","18","19","20","9.0","9.1","9.2","9.3","9.4","9.5","9.6"],"Locales":["en","zh-Hans"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}