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Short Description

Waiting for I/O on a data page.

Additional Information

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 an disk IO has been issued and we are waiting for it to complete so it can be written into shared_buffer memory.

How to reduce this wait

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

  • 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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