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Add /dev/zero mention for anon mmap().
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Bruce Momjian
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@ -482,3 +482,96 @@ TIP 6: Have you searched our list archives?
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http://archives.postgresql.org
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From pgsql-hackers-owner+M23388@postgresql.org Mon Jun 3 17:54:43 2002
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Return-path: <pgsql-hackers-owner+M23388@postgresql.org>
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Received: [from pobox.mot.com (pobox.mot.com [129.188.137.100]) by motgate3.mot.com (motgate3 2.1) with ESMTP id OAA22235; Mon, 3 Jun 2002 14:52:44 -0700 (MST)]
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Mon, 3 Jun 2002 16:52:57 -0500 (CDT)
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Message-ID: <0e0a01c20b49$26e90a00$22c30191@comm.mot.com>
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From: "Igor Kovalenko" <Igor.Kovalenko@motorola.com>
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To: "Bruce Momjian" <pgman@candle.pha.pa.us>
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cc: "Tom Lane" <tgl@sss.pgh.pa.us>, "mlw" <markw@mohawksoft.com>,
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"Marc G. Fournier" <scrappy@hub.org>, <pgsql-hackers@postgresql.org>
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References: <200206030047.g530lZi21901@candle.pha.pa.us>
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Subject: Re: [HACKERS] HEADS UP: Win32/OS2/BeOS native ports
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Date: Mon, 3 Jun 2002 16:53:51 -0500
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Status: OR
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That's what Apache does. Note, on most platforms MAP_ANON is equivalent to
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mmmap-ing /dev/zero. Solaris for example does not provide MAP_ANON but using
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fd=open(/dev/zero)
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mmap(fd, ...)
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close(fd)
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works just fine.
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----- Original Message -----
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From: "Bruce Momjian" <pgman@candle.pha.pa.us>
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To: "Igor Kovalenko" <Igor.Kovalenko@motorola.com>
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Cc: "Tom Lane" <tgl@sss.pgh.pa.us>; "mlw" <markw@mohawksoft.com>; "Marc G.
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Fournier" <scrappy@hub.org>; <pgsql-hackers@postgresql.org>
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Sent: Sunday, June 02, 2002 7:47 PM
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Subject: Re: [HACKERS] HEADS UP: Win32/OS2/BeOS native ports
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> Igor Kovalenko wrote:
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> > It does not have to be anonymous. POSIX also defines shm_open(same
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arguments
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> > as open) API which will create named object in whatever location
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corresponds
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> > to shared memory storage on that platform (object is then grown to
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needed
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> > size by ftruncate() and the fd is then passed to mmap). The object will
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> > exist in name space and can be detected by subsequent calls to
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shm_open()
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> > with same name. It is not really different from doing open(), but more
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> > portable (mmap() on regular files may not be supported).
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>
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> Actually, I think the best shared memory implemention would be
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> MAP_ANON | MAP_SHARED mmap(), which could be called from the postmaster
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> and passed to child processes.
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>
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> While all our platforms have mmap(), many don't have MAP_ANON, but those
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> that do could use it. You need MAP_ANON to prevent the shared memory
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> from being written to a disk file.
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>
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> --
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> Bruce Momjian | http://candle.pha.pa.us
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> pgman@candle.pha.pa.us | (610) 853-3000
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> + If your life is a hard drive, | 830 Blythe Avenue
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> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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>
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