Technologies/PostgreSQL/postgresql.blocks_hit

PostgreSQLMetric

postgresql.blocks_hit

Buffer cache hits

Dimensions:None

Available on:Native (1)

Datadog (1)

Interface Metrics (2)

Native

blks_hit

Number of buffer hits (blocks found in cache)

Dimensions:None

Datadog

postgresql.queries.shared_blks_hit

Total number of shared block cache hits per query_signature, db, and user. (DBM only)

Dimensions:None

Sources

blks_hitgithub.com

postgresql.queries.shared_blks_hitgithub.com

Technical Annotations (21)

Configuration Parameters (3)

shared_buffers

size of PostgreSQL buffer cache in memory

effective_cache_sizerecommended: 50-75% of total RAM

planner estimate of OS and PostgreSQL cache

enable_seqscanrecommended: false

Session-level override to force index usage when sequential scans perform poorly

CLI Commands (7)

SELECT sum(blks_hit) * 100.0 / sum(blks_hit + blks_read) as buffer_hit_ratio FROM pg_stat_database;diagnostic

SELECT relname, heap_blks_hit * 100.0 / nullif(heap_blks_hit + heap_blks_read, 0) as hit_ratio FROM pg_statio_user_tables WHERE heap_blks_read > 0 ORDER BY hit_ratio;

diagnostic

SELECT pg_reload_conf();remediation

SELECT round(blks_hit*100/(blks_hit+blks_read), 2) AS cache_hit_ratio FROM pg_stat_database WHERE datname = current_database();

diagnostic

ALTER SYSTEM SET shared_buffers = '16GB';remediation

EXPLAINdiagnostic

set enable_seqscan = false;remediation

Technical References (11)

shared_bufferscomponentpg_stat_databasecomponentpg_statio_user_tablescomponentOS Page CachecomponentCache Hit Ratioconceptdead tuplesconceptbuffer hitsconceptshared bufferscomponentpg_buffercachecomponentpg_prewarmcomponentcache hit ratioconcept

Related Insights (10)

Cache hit ratio below optimal causes excessive disk I/Owarning

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Low buffer hit ratio indicates insufficient shared_buffers or cache pressurewarning

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Insufficient shared_buffers causes excessive disk reads and slow querieswarning

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Insufficient shared_buffers limits PostgreSQL cache effectivenesswarning

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Cache hit ratio below 99% indicates undersized shared_buffers or high disk I/Owarning

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Slow queries caused by dead tuples, invalid queries, or misconfigurationwarning

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Insufficient shared_buffers causes excessive disk I/Owarning

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Sequential scans load entire table into shared buffers memory areainfo

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Cold buffer cache causes dramatic sequential scan performance degradationwarning

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Cache hit ratio below 99% indicates insufficient shared_buffers memorywarning

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