From: | Rébeli-Szabó Tamás <t(at)rblst(dot)info> |
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To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | How to calculate shared memory size |
Date: | 2020-09-15 14:12:39 |
Message-ID: | cdaa511e1909ef15b2d8f86aa4330a9b@rblst.info |
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Lists: | pgsql-general |
Hello all,
I want to do a proper calculation of the number of huge pages needed for
PostgreSQL to start.
For that I need to know how much shared memory will be allocated at
startup.
Looking at the shared memory calculation in the source (ipci.c), I can
see that two terms stand out:
size = add_size(size, BufferShmemSize()); ---> shared_buffers
size = add_size(size, XLOGShmemSize()); --> 1/32 * shared_buffers, but
max WAL segment size
However, if I only use those two terms (shared buffers + WAL segment
size) for my calculation, the result will be off by a lot, especially
with bigger shared buffers (e.g. 32 GB).
What are any other major terms (in the order of 10 megabytes or more)
that I need to take into account to get a better result?
Regards,
tamas
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