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To: pgsql-docs@lists.postgresql.org
Cc: splarv@ya.ru
Subject: vm.overcommit_ratio
Date: Thu, 26 Dec 2024 07:44:33 +0000
Message-ID: <173519907373.680.4776998956524739143@wrigleys.postgresql.org> (raw)
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/16/kernel-resources.html
Description:
PostgreSQL documentation point to kernel documentation for info about
vm.overcommit_ratio. But kernel documentation slightly incorrect, so may be
write slightly more here. Kernel documentation said:
The total address space commit
for the system is not permitted to exceed swap + a
configurable amount (default is 50%) of physical RAM.
Where 50% is the default for vm.overcommit_ratio. But really not "physical
RAM" is taken in case when using hugepage memory (common practice for
postgresql). For instance I have 1TiB physical memory and 800 GiB is
reserved for hugepage (1GiB pagesize). "50% of physical RAM" will be not 500
GiB, as expected, but roughly 100GiB=0.5*(1000-800), and commit limit will
be 100GiB+swap size.
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To: pgsql-docs@postgresql.org
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Subject: Re: vm.overcommit_ratio
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