BufferIO
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.
Additional Links​
PostgreSQL documentation - The Statistics Collector
habr.com - Locks in PostgreSQL: 4. Locks in memory
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