{"Entry":{"collection":"waitevent","key":"lwlock/BufferMapping","name":"BufferMapping","aliases":["BufferMapping","buffer_mapping"],"metadata":{"aliases":["BufferMapping","buffer_mapping"],"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":"buffer_mapping","to":"BufferMapping"},"reworded":null,"status":"changed","to":"13"}],"content_hash":"8b9beb3fa8232ecc7bcfcdec81f7ccb7fdf45194852bb5f9bbca63b373644c80","dossier":{"actions":{"en":["Correlate with buffer hit ratio and read volume by database and statement.","Look for a new scan, undersized cache, or concurrency jump.","Reduce concurrent scan fan-out or fix the access path before simply enlarging shared_buffers."],"zh":["按数据库与语句关联缓冲命中率和读取量。","检查是否出现新扫描、缓存过小或并发突增。","先降低并发扫描扇出或修正访问路径，再决定是否扩大 shared_buffers。"]},"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 = 'BufferMapping'\nORDER BY query_age DESC NULLS LAST;","title":"Sessions waiting on LWLock/BufferMapping","title_zh":"正在等待 LWLock/BufferMapping 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 = 'BufferMapping'\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":["shared_buffers","max_parallel_workers_per_gather"],"incident_pattern":{"en":"A plan regression launches many concurrent large scans; buffer-table partitions become hot while useful pages churn out of cache.","zh":"执行计划退化引发大量并发大扫描，缓冲映射分区变热，同时有用页面被挤出缓存。"},"mechanism":{"en":"The buffer manager hashes a relation/fork/block tag into a partition protected by BufferMappingLock. Lookup, insertion, eviction, and tag reassignment briefly take that partition lock; broad concurrent misses or buffer churn increase collisions.","zh":"缓冲区管理器把 relation/fork/block 标签哈希到由 BufferMappingLock 保护的分区。查找、插入、淘汰和重新分配标签都会短暂取得该分区锁；大规模并发未命中或缓冲区抖动会增加碰撞。"},"metrics":["waiting_sessions","wait_event_share","buffer_hit_ratio","blocks_read"],"normal":{"en":"Brief waits occur when pages enter or leave shared buffers.","zh":"页面进入或离开共享缓冲区时，短暂等待属于正常现象。"},"official_descriptions":{"13":"Waiting to associate a data block with a buffer in the buffer pool.","14":"Waiting to associate a data block with a buffer in the buffer pool.","15":"Waiting to associate a data block with a buffer in the buffer pool.","16":"Waiting to associate a data block with a buffer in the buffer pool.","17":"Waiting to associate a data block with a buffer in the buffer pool","18":"Waiting to associate a data block with a buffer in the buffer pool"},"record_kind":"event","source_locations":[{"commit":"724edf9bde9d356724ad384a2e196edc3c9f80f7","excerpt":"[LWTRANCHE_BUFFER_MAPPING] = \"BufferMapping\",","grep_pattern":"BufferMapping","grep_verified":true,"kind":"resource_path","line":152,"major":18,"path":"src/backend/storage/lmgr/lwlock.c","status":"dynamic_trigger","symbol":"BufferMapping","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/storage/lmgr/lwlock.c#L152","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":"BufferMapping\t\"Waiting to associate a data block with a buffer in the buffer pool.\"","grep_pattern":"BufferMapping","grep_verified":true,"kind":"catalog_definition","line":377,"major":18,"path":"src/backend/utils/activity/wait_event_names.txt","status":"dynamic_trigger","symbol":"BufferMapping","tag":"REL_18_6","url":"https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L377","version":"18.6"}],"source_status":"dynamic_trigger","trouble":{"en":"Sustained recurrence suggests a working set that churns through shared buffers, many parallel scans, or concentrated access mapping into a few partitions.","zh":"持续出现通常意味着工作集反复冲刷 shared buffers、大量并行扫描，或访问集中映射到少数分区。"}},"first_version":"9.6","has_dossier":true,"imported_at":"2026-09-27T17:57:32.88013+08:00","key":"lwlock/buffermapping","last_version":"20","name":"BufferMapping","position":210,"present_in":["9.6","10","11","12","13","14","15","16","17","18","19","20"],"slug":"buffer-mapping","source_rev":"english-manuals:726e1731f4a3ab5f1ffc2fad97ca932b2e943f4b9865973fa0e09075d62fceab","summary":"Waiting to associate a data block with a buffer in the buffer pool.","summary_zh":"","type":"LWLock","type_slug":"lwlock","type_variants":["LWLock","LWLockTranche"]}},"Definition":{"Collection":"waitevent","Key":"lwlock/BufferMapping","SourceDatabase":"center","Version":"18","SourceTable":"waitevent","SourceKey":"lwlock/buffermapping","SourceRevision":"english-manuals:726e1731f4a3ab5f1ffc2fad97ca932b2e943f4b9865973fa0e09075d62fceab","Facts":{"description":"Waiting to associate a data block with a buffer in the buffer pool.","description_zh":"","doc":{"anchor":"WAIT-EVENT-LWLOCK-TABLE","file":"monitoring-stats.html","lang":"en","sha256":"aa979eed08627fbf715a9d792094a162a73671db5af810f3ab2aad3e073d5722","slug":"18"},"lang":"en","name":"BufferMapping","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/BufferMapping","SourceDatabase":"pgweb","Version":"18","Locale":"zh-Hans","Title":"BufferMapping","Summary":"等待将数据块与缓冲池中的缓冲区关联。","BodyHTML":"\u003cp\u003e等待将数据块与缓冲池中的缓冲区关联。\u003c/p\u003e","SourceRevision":"2026-08-31@34d13c8","ContentHash":"8361bbfba66cc4cb336d6c6edc809debb8938abc9285074d12a10e0ed435ffc0","Payload":{"description_zh":"等待将数据块与缓冲池中的缓冲区关联。","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}