{"Entry":{"collection":"waitevent","key":"lwlock/WALBufMapping","name":"WALBufMapping","aliases":["WALBufMapping","WALBufMappingLock"],"metadata":{"aliases":["WALBufMapping","WALBufMappingLock"],"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":"WALBufMappingLock","to":"WALBufMapping"},"reworded":null,"status":"changed","to":"13"}],"content_hash":"a1e52c1d8e7e9bcdb79aa0bc85e77dce165cda29d1271c96211dfe61b6ba3b3b","dossier":{"actions":{"en":["Correlate with WAL bytes, WAL writes, and checkpoint timing.","Check whether wal_buffers is repeatedly exhausted during bursts.","Smooth write bursts and fix WAL device latency before tuning buffer size."],"zh":["关联 WAL 字节量、WAL 写入与检查点时间。","检查写突发期间 wal_buffers 是否反复耗尽。","先平滑写突发并解决 WAL 设备延迟，再调整缓冲区大小。"]},"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 = 'WALBufMapping'\nORDER BY query_age DESC NULLS LAST;","title":"Sessions waiting on LWLock/WALBufMapping","title_zh":"正在等待 LWLock/WALBufMapping 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 = 'WALBufMapping'\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":["wal_buffers","checkpoint_timeout","max_wal_size"],"incident_pattern":{"en":"A bulk load saturates WAL generation while the WAL device stalls, forcing frequent WAL buffer remapping.","zh":"批量导入把 WAL 生成推到极限，同时 WAL 设备发生停顿，导致频繁的 WAL 缓冲页重映射。"},"mechanism":{"en":"WALBufMappingLock coordinates the mapping between WAL page numbers and the finite wal_buffers slots. A backend needs it when advancing to or replacing a WAL buffer page.","zh":"WALBufMappingLock 协调 WAL 页号与有限 wal_buffers 槽位之间的映射。后端推进到新 WAL 页或替换缓冲页时需要取得此锁。"},"metrics":["waiting_sessions","wait_event_share","wal_bytes","wal_write_time"],"normal":{"en":"Short waits appear as WAL generation advances through buffer pages.","zh":"WAL 生成推进并跨越缓冲页时会短暂出现。"},"official_descriptions":{"13":"Waiting to replace a page in WAL buffers.","14":"Waiting to replace a page in WAL buffers.","15":"Waiting to replace a page in WAL buffers.","16":"Waiting to replace a page in WAL buffers.","17":"Waiting to replace a page in WAL buffers","18":"Waiting to replace a page in WAL buffers"},"record_kind":"event","source_locations":[{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"LWLockAcquire(WALBufMappingLock, LW_EXCLUSIVE);","grep_pattern":"WALBufMapping","grep_verified":true,"kind":"resource_path","line":1999,"major":18,"path":"src/backend/access/transam/xlog.c","status":"dynamic_trigger","symbol":"WALBufMapping","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/access/transam/xlog.c#L1999","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":"WALBufMapping\t\"Waiting to replace a page in WAL buffers.\"","grep_pattern":"WALBufMapping","grep_verified":true,"kind":"catalog_definition","line":319,"major":18,"path":"src/backend/utils/activity/wait_event_names.txt","status":"dynamic_trigger","symbol":"WALBufMapping","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L319","version":"18.6"}],"source_status":"dynamic_trigger","trouble":{"en":"Sustained contention suggests WAL generation is turning over buffers faster than the write path advances, often during write bursts or checkpoints.","zh":"持续竞争说明 WAL 生成换页速度超过写路径推进速度，常见于写突发或检查点期间。"}},"first_version":"9.6","has_dossier":true,"imported_at":"2026-09-27T17:57:33.075768+08:00","key":"lwlock/walbufmapping","last_version":"20","name":"WALBufMapping","position":283,"present_in":["9.6","10","11","12","13","14","15","16","17","18","19","20"],"slug":"wal-buf-mapping","source_rev":"english-manuals:42c560b9b7347809550e27387803de423d1d9eabe62cae895d850308de5e5ff7","summary":"Waiting to replace a page in WAL buffers.","summary_zh":"","type":"LWLock","type_slug":"lwlock","type_variants":["LWLock","LWLockNamed"]}},"Definition":{"Collection":"waitevent","Key":"lwlock/WALBufMapping","SourceDatabase":"center","Version":"18","SourceTable":"waitevent","SourceKey":"lwlock/walbufmapping","SourceRevision":"english-manuals:42c560b9b7347809550e27387803de423d1d9eabe62cae895d850308de5e5ff7","Facts":{"description":"Waiting to replace a page in WAL buffers.","description_zh":"","doc":{"anchor":"WAIT-EVENT-LWLOCK-TABLE","file":"monitoring-stats.html","lang":"en","sha256":"aa979eed08627fbf715a9d792094a162a73671db5af810f3ab2aad3e073d5722","slug":"18"},"lang":"en","name":"WALBufMapping","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/WALBufMapping","SourceDatabase":"pgweb","Version":"18","Locale":"zh-Hans","Title":"WALBufMapping","Summary":"等待在WAL缓冲区中替换一个页面。","BodyHTML":"\u003cp\u003e等待在WAL缓冲区中替换一个页面。\u003c/p\u003e","SourceRevision":"2026-08-31@34d13c8","ContentHash":"049f9d0367ca926d0863cd3b299a10ef27cb802b69595eb6af4380daee1db5d5","Payload":{"description_zh":"等待在WAL缓冲区中替换一个页面。","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}