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Short Description

Waiting to read or write a data page in memory.

Detailed Description

The server process is waiting for a lightweight lock (LWLock). LWLocks are similar to latches in other database systems. Most such locks protect a particular data structure in shared memory. There is no order to the granting of LWLocks and in a high concurrency system this can cause contention. In this case a we are waiting for access to a shared memory buffer.

How to reduce this wait

This is a very common wait as it forms part of any query.

  • Check for unused or duplicate indexes and remove if possible and use Partial Indexes if possible.
  • Watch out for foreign keys with comparatively few parent rows. The parent rows will have read locks applied whilst child operations take place.
  • Consider partitioning the
  • Compare with your baseline to see if this is exceptional or normal workload.
  • Check for many processes accessing the same resources concurrently.
  • Ensure the execution path of your query is efficient as possible.

PostgreSQL documentation - 27.2. The Statistics Collector - Locks in PostgreSQL: 4. Locks in memory

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