{"Entry":{"collection":"waitevent","key":"lwlock/MultiXactMemberSLRU","name":"MultiXactMemberSLRU","aliases":["MultiXactMemberControlLock","MultiXactMemberSLRU"],"metadata":{"aliases":["MultiXactMemberControlLock","MultiXactMemberSLRU"],"changed_in":["10","13"],"changes":[{"from":"9.6","moved":{"from":"LWLockNamed","to":"LWLock"},"renamed":null,"reworded":null,"status":"changed","to":"10"},{"from":"12","moved":null,"renamed":{"from":"MultiXactMemberControlLock","to":"MultiXactMemberSLRU"},"reworded":{"from":"Waiting to read or update multixact member mappings.","to":"Waiting to access the multixact member SLRU cache."},"status":"changed","to":"13"}],"content_hash":"86421e3578d45e768dc25eba9014ca4966a7b4bea18ab4539e1bb6d259a330a2","dossier":{"actions":{"en":["Find statements and tables creating many shared row locks.","Check multixact age and autovacuum progress.","Reduce lock fan-out and unblock multixact freeze; investigate member SLRU I/O if paired with buffer waits."],"zh":["找出制造大量共享行锁的语句与表。","检查 multixact 年龄与 autovacuum 进度。","降低锁扇出并解除 multixact 冻结阻塞；若同时出现 buffer 等待，再查 member SLRU I/O。"]},"diagnostic_sql":[{"id":"sessions","min_version":"13","sql":"SELECT pid, backend_type, usename, datname, application_name,\n       state, now() - query_start AS query_age,\n       now() - xact_start AS xact_age,\n       wait_event_type, wait_event,\n       pg_blocking_pids(pid) AS blocking_pids,\n       left(query, 160) AS query\nFROM pg_stat_activity\nWHERE wait_event_type = 'LWLock'\n  AND wait_event = 'MultiXactMemberSLRU'\nORDER BY query_age DESC NULLS LAST;","title":"Sessions waiting on LWLock/MultiXactMemberSLRU","title_zh":"正在等待 LWLock/MultiXactMemberSLRU 的会话"},{"id":"cohort","min_version":"13","sql":"SELECT wait_event, count(*) AS waiting_sessions,\n       count(*) FILTER (WHERE state = 'active') AS active_waiters,\n       max(now() - query_start) AS oldest_query\nFROM pg_stat_activity\nWHERE wait_event_type = 'LWLock'\nGROUP BY wait_event\nORDER BY waiting_sessions DESC, wait_event;","title":"Current LWLock cohort","title_zh":"当前 LWLock 等待分布"},{"id":"lock_objects","min_version":"13","sql":"SELECT a.pid, l.locktype, l.mode, l.granted, l.fastpath,\n       d.datname, n.nspname, c.relname,\n       l.page, l.tuple, l.virtualxid, l.transactionid,\n       l.classid, l.objid, l.objsubid\nFROM pg_stat_activity AS a\nLEFT JOIN pg_locks AS l ON l.pid = a.pid\nLEFT JOIN pg_database AS d ON d.oid = l.database\nLEFT JOIN pg_class AS c\n  ON c.oid = l.relation\n AND l.database = (\n       SELECT oid FROM pg_database WHERE datname = current_database()\n     )\nLEFT JOIN pg_namespace AS n ON n.oid = c.relnamespace\nWHERE a.wait_event_type = 'LWLock'\n  AND a.wait_event = 'MultiXactMemberSLRU'\nORDER BY a.pid, l.granted, l.locktype, l.mode;","title":"Lock and relation context for these sessions","title_zh":"这些会话的锁与关系上下文"}],"emission":{"status":"active","verified_release":"18.6"},"gucs":["autovacuum_multixact_freeze_max_age","vacuum_multixact_freeze_table_age"],"incident_pattern":{"en":"A high-fan-out foreign-key workload locks many parent rows while a long transaction delays multixact cleanup, driving member-cache contention.","zh":"高扇出的外键负载锁住大量父表行，同时长事务推迟 multixact 清理，最终引发 member 缓存竞争。"},"mechanism":{"en":"This lock protects the SLRU cache for pg_multixact/members, which stores the transaction members of multitransaction IDs used by shared row locks. Concurrent row-lock creation and old member lookups meet here.","zh":"此锁保护 pg_multixact/members 的 SLRU 缓存；这里保存共享行锁使用的 multitransaction ID 成员事务。并发行锁创建与旧成员查询会在这里相遇。"},"metrics":["waiting_sessions","wait_event_share","oldest_multixact_age","multixact_member_io"],"normal":{"en":"Brief waits occur in workloads that use SELECT FOR SHARE/KEY SHARE or create multixacts through foreign-key checks.","zh":"使用 SELECT FOR SHARE/KEY SHARE，或因外键检查创建 multixact 的负载中会短暂出现。"},"official_descriptions":{"13":"Waiting to access the multixact member SLRU cache.","14":"Waiting to access the multixact member SLRU cache.","15":"Waiting to access the multixact member SLRU cache.","16":"Waiting to access the multixact member SLRU cache.","17":"Waiting to access the multixact member SLRU cache","18":"Waiting to access the multixact member SLRU cache"},"record_kind":"event","source_locations":[{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"[LWTRANCHE_MULTIXACTMEMBER_SLRU] = \"MultiXactMemberSLRU\",","grep_pattern":"MultiXactMemberSLRU","grep_verified":true,"kind":"resource_path","line":174,"major":18,"path":"src/backend/storage/lmgr/lwlock.c","status":"dynamic_trigger","symbol":"MultiXactMemberSLRU","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/storage/lmgr/lwlock.c#L174","version":"18.6"},{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"pgstat_report_wait_start(PG_WAIT_LWLOCK | lock-\u003etranche);","grep_pattern":"pgstat_report_wait_start","grep_verified":true,"kind":"generic_reporter","line":739,"major":18,"path":"src/backend/storage/lmgr/lwlock.c","status":"dynamic_trigger","symbol":"pgstat_report_wait_start","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/storage/lmgr/lwlock.c#L739","version":"18.6"},{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"MultiXactMemberSLRU\t\"Waiting to access the multixact member SLRU cache.\"","grep_pattern":"MultiXactMemberSLRU","grep_verified":true,"kind":"catalog_definition","line":399,"major":18,"path":"src/backend/utils/activity/wait_event_names.txt","status":"dynamic_trigger","symbol":"MultiXactMemberSLRU","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L399","version":"18.6"}],"source_status":"dynamic_trigger","trouble":{"en":"Sustained contention points to heavy shared row locking, multixact churn, lagging freeze, or slow pg_multixact storage.","zh":"持续竞争指向大量共享行锁、multixact 抖动、冻结落后，或 pg_multixact 存储缓慢。"}},"first_version":"9.6","has_dossier":true,"imported_at":"2026-09-27T17:57:32.92449+08:00","key":"lwlock/multixactmemberslru","last_version":"20","name":"MultiXactMemberSLRU","position":232,"present_in":["9.6","10","11","12","13","14","15","16","17","18","19","20"],"slug":"multi-xact-member-slru","source_rev":"english-manuals:e65cb993b4ecd947f05f6858812a3e20b4fb4da683e3e8c1310542c824bcc1e9","summary":"Waiting to access the multixact member SLRU cache.","summary_zh":"","type":"LWLock","type_slug":"lwlock","type_variants":["LWLock","LWLockNamed"]}},"Definition":{"Collection":"waitevent","Key":"lwlock/MultiXactMemberSLRU","SourceDatabase":"center","Version":"18","SourceTable":"waitevent","SourceKey":"lwlock/multixactmemberslru","SourceRevision":"english-manuals:e65cb993b4ecd947f05f6858812a3e20b4fb4da683e3e8c1310542c824bcc1e9","Facts":{"description":"Waiting to access the multixact member SLRU cache.","description_zh":"","doc":{"anchor":"WAIT-EVENT-LWLOCK-TABLE","file":"monitoring-stats.html","lang":"en","sha256":"aa979eed08627fbf715a9d792094a162a73671db5af810f3ab2aad3e073d5722","slug":"18"},"lang":"en","name":"MultiXactMemberSLRU","source":"english-manual","type":"LWLock","zh_from":""},"ManualEvidence":{"doc":{"anchor":"WAIT-EVENT-LWLOCK-TABLE","file":"monitoring-stats.html","lang":"en","sha256":"aa979eed08627fbf715a9d792094a162a73671db5af810f3ab2aad3e073d5722","slug":"18"}},"MeasuredEvidence":{}},"Text":{"Collection":"waitevent","Key":"lwlock/MultiXactMemberSLRU","SourceDatabase":"pgweb","Version":"18","Locale":"zh-Hans","Title":"MultiXactMemberSLRU","Summary":"等待访问多事务成员 SLRU 缓存。","BodyHTML":"\u003cp\u003e等待访问多事务成员 SLRU 缓存。\u003c/p\u003e","SourceRevision":"2026-08-31@34d13c8","ContentHash":"c696bde04a50e8dd58d37e62bd6c2f8fbee6db8048b1a0586063aa2c5c313f99","Payload":{"description_zh":"等待访问多事务成员 SLRU 缓存。","zh_from":"doc"}},"RequestedLocale":"zh-Hans","Fallback":false,"Versions":["10","11","12","13","14","15","16","17","18","19","20","9.6"],"Locales":["en","zh-Hans"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}