PostgreSQL on Linux: what is cached?

By Franck Pachot

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In a recent tweet I wanted to highlight the importance of knowing what you measure with pgbench, because looking at “Transactions per second” without knowing if you are in shared buffer cache hits, or filesystem cache hit, or storage cache hit, or physical read… is just meaningless:

When you run the #postgres builtin pgbench, you should know:
– the size of the dataset on disk, about 15MB x scale
– the size of accessed shared_buffers (I see about 90% of size for a select-only workload)
– the size cached by the filesystem (looks like I have 2x here

• buff/cache
• Cache
• free
• linux
• Postgres
• postgresql
• shared