By mapping the WAL files by each backend in to its address
space using "mmap" system call , there will be big
improvements in performance from the following point of view:
1. Each backend directly writes in to the address
space which is obtained by maping the WAL files.
this saves the write system call at the end of
every transaction which transfres 8k of
data from user space to kernel.
2. since every transaction does not modify all the 8k
content of WAL page , so by issuing the
fsync , the kernel only transfers only the
kernel pages which are modified , which is 4k for
linux so fsync time is saved by twice.
Any comments ?.
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