{"Entry":{"collection":"waitevent","key":"lwlock/MultiXactMemberBuffer","name":"MultiXactMemberBuffer","aliases":["MultiXactMemberBuffer","multixact_member"],"metadata":{"aliases":["MultiXactMemberBuffer","multixact_member"],"changed_in":["10","13"],"changes":[{"from":"9.6","moved":{"from":"LWLockTranche","to":"LWLock"},"renamed":null,"reworded":null,"status":"changed","to":"10"},{"from":"12","moved":null,"renamed":{"from":"multixact_member","to":"MultiXactMemberBuffer"},"reworded":{"from":"Waiting for I/O on a multixact_member buffer.","to":"Waiting for I/O on a multixact member SLRU buffer."},"status":"changed","to":"13"}],"content_hash":"db619cab1db0d1a1b0fd3bd970012431badc513dbf30db2b971bc8b1e433f5fc","dossier":{"actions":{"en":["Repeat the snapshot and isolate one hot tranche.","Correlate it with the protected resource and current workload phase.","Reduce the specific contention source; adding concurrency can make a shared-memory hotspot worse."],"zh":["重复采样并锁定一个热点 tranche。","把它与受保护资源及当前负载阶段关联。","降低具体竞争源；增加并发可能让共享内存热点更糟。"]},"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 = 'MultiXactMemberBuffer'\nORDER BY query_age DESC NULLS LAST;","title":"Sessions waiting on LWLock/MultiXactMemberBuffer","title_zh":"正在等待 LWLock/MultiXactMemberBuffer 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 = 'MultiXactMemberBuffer'\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":"","zh":""},"mechanism":{"en":"`pgstat_report_wait_start` at `src/backend/storage/lmgr/lwlock.c:739` is the grep-verified reporting path. The public identity/resource is mapped at `src/backend/storage/lmgr/lwlock.c:144`. The instrumented operation is: Waiting for I/O on a multixact member SLRU buffer. LWLockAcquire could not immediately take the lightweight-lock tranche displayed as MultiXactMemberBuffer. The generic LWLock reporter publishes the tranche name while the backend sleeps on the internal shared-memory resource.","zh":"`pgstat_report_wait_start` 位于 `src/backend/storage/lmgr/lwlock.c:739`，是经 grep 核验的报告路径。公共身份/资源映射位于 `src/backend/storage/lmgr/lwlock.c:144`。探针覆盖的操作是：等待 multixact member SLRU buffer 上的 I/O。LWLockAcquire 无法立即取得显示为 MultiXactMemberBuffer 的轻量级锁 tranche；后端在内部共享内存资源上休眠时，通用 LWLock 报告器发布该 tranche 名称。"},"metrics":["waiting_sessions","wait_event_share","oldest_multixact_age"],"normal":{"en":"A brief sample is normal around short internal critical sections.","zh":"短暂内部临界区周围的零星样本属于正常。"},"official_descriptions":{"13":"Waiting for I/O on a multixact member SLRU buffer.","14":"Waiting for I/O on a multixact member SLRU buffer.","15":"Waiting for I/O on a multixact member SLRU buffer.","16":"Waiting for I/O on a multixact member SLRU buffer.","17":"Waiting for I/O on a multixact member SLRU buffer","18":"Waiting for I/O on a multixact member SLRU buffer"},"record_kind":"event","source_locations":[{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"[LWTRANCHE_MULTIXACTMEMBER_BUFFER] = \"MultiXactMemberBuffer\",","grep_pattern":"MultiXactMemberBuffer","grep_verified":true,"kind":"resource_path","line":144,"major":18,"path":"src/backend/storage/lmgr/lwlock.c","status":"dynamic_trigger","symbol":"MultiXactMemberBuffer","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/storage/lmgr/lwlock.c#L144","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":"MultiXactMemberBuffer\t\"Waiting for I/O on a multixact member SLRU buffer.\"","grep_pattern":"MultiXactMemberBuffer","grep_verified":true,"kind":"catalog_definition","line":369,"major":18,"path":"src/backend/utils/activity/wait_event_names.txt","status":"dynamic_trigger","symbol":"MultiXactMemberBuffer","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L369","version":"18.6"}],"source_status":"dynamic_trigger","trouble":{"en":"Investigate when the same tranche affects at least 10% of active foreground sessions in three consecutive one-second samples; treat 25% or waits beyond five seconds as urgent.","zh":"若同一 tranche 在连续三次一秒采样中影响至少 10% 的活动前台会话，应当调查；达到 25% 或持续超过五秒按紧急处理。"}},"first_version":"9.6","has_dossier":true,"imported_at":"2026-09-27T17:57:32.922303+08:00","key":"lwlock/multixactmemberbuffer","last_version":"20","name":"MultiXactMemberBuffer","position":231,"present_in":["9.6","10","11","12","13","14","15","16","17","18","19","20"],"slug":"multi-xact-member-buffer","source_rev":"english-manuals:d8ce3918d14b058d490a3f815e23ae1cfe6284ac3580ef2db4df0075174ef8be","summary":"Waiting for I/O on a multixact member SLRU buffer.","summary_zh":"","type":"LWLock","type_slug":"lwlock","type_variants":["LWLock","LWLockTranche"]}},"Definition":{"Collection":"waitevent","Key":"lwlock/MultiXactMemberBuffer","SourceDatabase":"center","Version":"18","SourceTable":"waitevent","SourceKey":"lwlock/multixactmemberbuffer","SourceRevision":"english-manuals:d8ce3918d14b058d490a3f815e23ae1cfe6284ac3580ef2db4df0075174ef8be","Facts":{"description":"Waiting for I/O on a multixact member SLRU buffer.","description_zh":"","doc":{"anchor":"WAIT-EVENT-LWLOCK-TABLE","file":"monitoring-stats.html","lang":"en","sha256":"aa979eed08627fbf715a9d792094a162a73671db5af810f3ab2aad3e073d5722","slug":"18"},"lang":"en","name":"MultiXactMemberBuffer","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/MultiXactMemberBuffer","SourceDatabase":"pgweb","Version":"18","Locale":"zh-Hans","Title":"MultiXactMemberBuffer","Summary":"等待多事务成员 SLRU 缓冲区上的 I/O。","BodyHTML":"\u003cp\u003e等待多事务成员 SLRU 缓冲区上的 I/O。\u003c/p\u003e","SourceRevision":"2026-08-31@34d13c8","ContentHash":"314455044616ec552ba0f74ce3b2d987d80556d00aed0d29b7c1b442b413a0e7","Payload":{"description_zh":"等待多事务成员 SLRU 缓冲区上的 I/O。","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}