#PostgreSQL writes to disk, it executes one of the system fsync calls (fsync or fdatasync) to flush that data to disk. By
default, the cache on hard disks and disk controllers are assumed to be
volatile: when power fails, data written there will be lost. Since that
can result in filesystem and/or database corruption when it happens,
fsync in Linux issues a write barrier that forces all data onto physical
disk. That will flush the write cache on both RAID and drive write
caches.
#syscalls
https://avidandrew.com/understanding-disk-cache-writeback-ext4.html
avidandrew.comUnderstanding Disk Caches, The Journal, Barriers, and Writeback Using QEMU/KVM and EXT4 - Avid AndrewThere are multiple layers of caching involved when writing a file before it makes it to permanent storage on your disk. This becomes even more complicated with a virtual machine which has its own set of caches. Let's explore how exactly writes make it safely to your disk, both on a physical server and a VM.
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