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Short Description

Waiting for I/O on a data page.

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

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