From: J Lumby <johnlumby@hotmail.com>
To: Peng Yu <pengyu.ut@gmail.com>
Cc: Peng Yu via Libc-help <libc-help@sourceware.org>,
Florian Weimer <fweimer@redhat.com>
Subject: Re: What is the point of IPC_PRIVATE of shmget?
Date: Mon, 12 Apr 2021 14:17:46 -0400 [thread overview]
Message-ID: <DM6PR06MB5562DAA98DFFCC08B96C9831A3709@DM6PR06MB5562.namprd06.prod.outlook.com> (raw)
In-Reply-To: <CABrM6wmFq3Nqs-5uQ3TEaHCrzrPABeUsS6pFcTxpf6fyLMJ23Q@mail.gmail.com>
For the (common) case of parent process which forks children and wants
all to be able to access common memory, another alternative is to use
mmap. postgresql used to use shmget but since V9.3 has switched most
shared memory areas to mmap. Here is why:
from src/backend/port/sysv_shmem.c
* This works around the problem that many
* systems have very low limits on the amount of System V shared memory
* that can be allocated. Even a limit of a few megabytes will be enough
* to run many copies of PostgreSQL without needing to adjust system
settings.
Cheers, John
On 4/12/21 1:23 PM, Peng Yu via Libc-help wrote:
>> Oh, it can be shared if the process forks. With malloc, you'd lose the
>> sharing.
> OK. This makes much more sense now.
>
next prev parent reply other threads:[~2021-04-12 18:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 15:54 Peng Yu
2021-04-12 16:06 ` tomas
2021-04-12 16:07 ` Florian Weimer
2021-04-12 16:12 ` Peng Yu
2021-04-12 16:14 ` Florian Weimer
2021-04-12 16:18 ` Florian Weimer
2021-04-12 17:23 ` Peng Yu
2021-04-12 18:17 ` J Lumby [this message]
2021-04-12 17:55 ` Manfred
2021-04-12 19:05 ` Peng Yu
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