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The locks collector exposes metrics about PostgreSQL locks held by database connections.

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Status

Default: Enabled

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Metrics

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pg_locks_count

Type: Gauge
Description: Number of locks currently held Labels:
  • datname - Database name
  • mode - Lock mode (see below)

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Lock Modes

The collector tracks all PostgreSQL lock modes:
  • accesssharelock - Acquired by SELECT statements
  • rowsharelock - Acquired by SELECT FOR UPDATE/SHARE
  • rowexclusivelock - Acquired by UPDATE, DELETE, INSERT
  • shareupdateexclusivelock - Acquired by VACUUM, CREATE INDEX CONCURRENTLY
  • sharelock - Acquired by CREATE INDEX
  • sharerowexclusivelock - Acquired by CREATE TRIGGER
  • exclusivelock - Blocks concurrent SELECT FOR UPDATE
  • accessexclusivelock - Acquired by DROP TABLE, TRUNCATE, VACUUM FULL, LOCK TABLE
  • sireadlock - Used by serializable transactions

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SQL Query

SELECT 
  pg_database.datname as datname,
  tmp.mode as mode,
  COALESCE(count, 0) as count 
FROM 
  (
    VALUES 
      ('accesssharelock'), 
      ('rowsharelock'), 
      ('rowexclusivelock'), 
      ('shareupdateexclusivelock'), 
      ('sharelock'), 
      ('sharerowexclusivelock'), 
      ('exclusivelock'), 
      ('accessexclusivelock'), 
      ('sireadlock')
  ) AS tmp(mode)
  CROSS JOIN pg_database 
  LEFT JOIN (
    SELECT 
      database, 
      lower(mode) AS mode, 
      count(*) AS count 
    FROM 
      pg_locks 
    WHERE 
      database IS NOT NULL 
    GROUP BY 
      database, 
      lower(mode)
  ) AS tmp2 ON tmp.mode = tmp2.mode 
  and pg_database.oid = tmp2.database 
ORDER BY 1

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PostgreSQL Versions

Supported: All versions

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Required Permissions

The monitoring user needs:
  • Access to pg_locks view
  • Access to pg_database catalog

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Example Output

pg_locks_count{datname="myapp",mode="accesssharelock"} 25
pg_locks_count{datname="myapp",mode="rowexclusivelock"} 3
pg_locks_count{datname="myapp",mode="accessexclusivelock"} 0

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Use Cases

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Detecting Lock Contention

High lock counts can indicate:
  • Long-running transactions
  • Lock contention and blocking queries
  • Connection pooling issues
  • DDL operations blocking queries

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Monitoring Patterns

# High exclusive locks
pg_locks_count{mode="accessexclusivelock"} > 5

# Total locks per database
sum by (datname) (pg_locks_count)

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