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Planet PostgreSQL0 Hot0 comments6 min read
All Your GUCs in a Row: notify_buffers
A deep benchmark-driven investigation of PostgreSQL's notify_buffers GUC, which sizes the SLRU cache behind the LISTEN/NOTIFY queue. Testing across PostgreSQL 18.6 and 19 beta 4 shows the default 128kB cache (16 buffers) almost never causes measurable slowdowns, with misses costing only about two microseconds more than hits. The only workload where the setting moved throughput noticeably (around 10%) was near-maximum-size payloads filling a queue page every commit. The real bottleneck for slow NOTIFY turns out to be cluster-wide commit locking and, through PostgreSQL 18, every commit signaling all listeners in a database regardless of channel - a problem PostgreSQL 19 fixes by waking only relevant listeners. The piece also notes that since the February 2026 minor releases, VACUUM advancing datfrozenxid now scans the whole notify queue as part of a fix for prior 'could not access status of transaction' errors.
Source: https://postgr.es/p/9x2. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.
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