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I wrote:
> scott.marlowe wrote:
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> On Fri, 13 Sep 2002, Justin Clift wrote:
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Curt Sampson <cjs@cynic.net> writes:
> On Thu, 12 Sep 2002, Justin Clift wrote:
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On Wed, Sep 18, 2002 at 08:01:42PM -0400, Bruce Momjian wrote:
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-From mascarm@mascari.com Thu Sep 19 01:24:42 2002
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-Date: Thu, 19 Sep 2002 01:23:45 -0400
-From: Mike Mascari <mascarm@mascari.com>
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-To: Bruce Momjian <pgman@candle.pha.pa.us>
-cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-References: <200209190001.g8J01gG13849@candle.pha.pa.us>
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-Bruce Momjian wrote:
-> I am working with several groups getting the Win32 port ready for 7.4
-> and I have a few questions:
->
-> What is the standard workaround for the fact that rename() isn't atomic
-> on Win32? Do we need to create our own locking around the
-> reading/writing of files that are normally updated in place using
-> rename()?
-
-Visual C++ comes with the source to Microsoft's C library:
-
-rename() calls MoveFile() which will error if:
-
-1. The target file exists
-2. The source file is in use
-
-MoveFileEx() (not available on 95/98) can overwrite the target
-file if it exists. The Apache APR portability library uses
-MoveFileEx() to rename files if under NT/XP/2K vs. a sequence of :
-
-1. CreateFile() to test for target file existence
-2. DeleteFile() to remove the target file
-3. MoveFile() to rename the old file to new
-
-under Windows 95/98. Of course, some other process could create
-the target file between 2 and 3, so their rename() would just
-error out in that situation. I haven't tested it, but I recall
-reading somewhere that MoveFileEx() has the ability to rename an
-opened file. I'm 99% sure MoveFile() will fail if the source
-file is open.
-
->
-> Second, when you unlink() a file on Win32, do applications continue
-> accessing the old file contents if they had the file open before the
-> unlink?
->
-
-unlink() just calls DeleteFile() which will error if:
-
-1. The target file is in use
-
-CreateFile() has the option:
-
-FILE_FLAG_DELETE_ON_CLOSE
-
-which might be able to be used to simulate traditional unlink()
-behavior.
-
-Hope that helps,
-
-Mike Mascari
-mascarm@mascari.com
-
-
-
-
-
-
-
-
-
-
From pgsql-hackers-owner+M29091@postgresql.org Thu Sep 19 01:24:54 2002
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Bruce Momjian wrote:
> I am working with several groups getting the Win32 port ready for 7.4
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> On Wed, Sep 18, 2002 at 08:01:42PM -0400, Bruce Momjian wrote:
>
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Christopher Kings-Lynne wrote:
>>On Wed, Sep 18, 2002 at 08:01:42PM -0400, Bruce Momjian wrote:
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Mike Mascari wrote:
> Bruce Momjian wrote:
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-
-Bruce Momjian wrote:
-> > > Second, when you unlink() a file on Win32, do applications continue
-> > > accessing the old file contents if they had the file open before the
-> > > unlink?
-> > >
-> >
-> > unlink() just calls DeleteFile() which will error if:
-> >
-> > 1. The target file is in use
-> >
-> > CreateFile() has the option:
-> >
-> > FILE_FLAG_DELETE_ON_CLOSE
-> >
-> > which might be able to be used to simulate traditional unlink()
-> > behavior.
->
-> No, that flag isn't going to help us. I wonder what MoveFileEx does if
-> the target file exists _and_ is open by another user? I don't see any
-> loop in that Win32 rename() routine, and I looked at the Unix version of
-> apr_file_rename and its just a straight rename() call.
-
-This says that if the target is in use, it is overwritten:
-
- http://support.microsoft.com/default.aspx?scid=KB;EN-US;q140570&
-
-While I think that is good news, does it open the problem of other
-readers reading partial updates to the file and therefore seeing
-garbage. Not sure how to handle that, nor am I even sure how I would
-test it.
-
---
- Bruce Momjian | http://candle.pha.pa.us
- pgman@candle.pha.pa.us | (610) 359-1001
- + If your life is a hard drive, | 13 Roberts Road
- + Christ can be your backup. | Newtown Square, Pennsylvania 19073
-
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-From: Bruce Momjian <pgman@candle.pha.pa.us>
-Message-ID: <200209200250.g8K2ofr29042@candle.pha.pa.us>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-In-Reply-To: <200209192024.g8JKO1g10337@candle.pha.pa.us>
-To: Bruce Momjian <pgman@candle.pha.pa.us>
-Date: Thu, 19 Sep 2002 22:50:41 -0400 (EDT)
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Bruce Momjian wrote:
> > > Second, when you unlink() a file on Win32, do applications continue
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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From mascarm@mascari.com Fri Sep 20 00:02:33 2002
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Bruce Momjian wrote:
> Bruce Momjian wrote:
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Mike Mascari wrote:
> I read the article and did not come away with that conclusion.
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Bruce Momjian wrote:
> Mike Mascari wrote:
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-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
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- <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-References: <200209200405.g8K45RV12655@candle.pha.pa.us> <3D8AA4B2.8090507@mascari.com>
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-
-Mike Mascari wrote:
-> Bruce Momjian wrote:
->
->> Mike Mascari wrote:
->>
->>> I will do some testing with concurrency and let you know. But don't
->>> get your hopes up. This is one of the many advantages that
->>> TABLESPACEs have when more than one relation is stored in a single
->>> DATAFILE. There was Oracle for MS-DOS, after all..
->>
->>
->>
->> I was focusing on handling of pg_pwd and other config file that are
->> written by various backend while other backends are reading them. The
->> actual data files should be OK because we have an exclusive lock when we
->> are adding/removing them.
->>
->
-> OK. So you want to test:
->
-> 1. Process 1 opens "foo"
-> 2. Process 2 opens "foo"
-> 3. Process 1 renames "foo" to "bar"
-> 4. Process 2 can safely read from its open file handle
-
-Actually, looking at the pg_pwd code, you want to determine a
-way for:
-
-1. Process 1 opens "foo"
-2. Process 2 opens "foo"
-3. Process 1 creates "bar"
-4. Process 1 renames "bar" to "foo"
-5. Process 2 can continue to read data from the open file handle
-and get the original "foo" data.
-
-Is that correct?
-
-Mike Mascari
-mascarm@mascari.com
-
-
From pgsql-hackers-owner+M29180@postgresql.org Fri Sep 20 01:02:47 2002
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Mike Mascari wrote:
> Bruce Momjian wrote:
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Mike Mascari wrote:
> Actually, looking at the pg_pwd code, you want to determine a
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Bruce Momjian wrote:
> Mike Mascari wrote:
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-
-On Fri, 20 Sep 2002, Mike Mascari wrote:
-
-> Bruce Momjian wrote:
-> > Mike Mascari wrote:
-> >
-> >>Actually, looking at the pg_pwd code, you want to determine a
-> >>way for:
-> >>
-> >>1. Process 1 opens "foo"
-> >>2. Process 2 opens "foo"
-> >>3. Process 1 creates "bar"
-> >>4. Process 1 renames "bar" to "foo"
-> >>5. Process 2 can continue to read data from the open file handle
-> >>and get the original "foo" data.
-> >
-> >
-> > Yep, that's it.
-> >
->
-> So far, MoveFileEx("foo", "bar", MOVEFILE_REPLACE_EXISTING)
-> returns "Access Denied" when Process 1 attempts the rename. But
-> I'm continuing to investigate the possibilities...
-
-Does a sequence like
-Process 1 opens "foo"
-Process 2 opens "foo"
-Process 1 creates "bar"
-Process 1 renames "foo" to <something>
- - where something is generated to not overlap an existing file
-Process 1 renames "bar" to "foo"
-Process 2 continues reading
-let you do the replace and keep reading (at the penalty that
-you've now got to have a way to know when to remove the
-various <something>s)
-
-
-
-From pgsql-hackers-owner+M29183@postgresql.org Fri Sep 20 01:50:47 2002
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On Fri, 20 Sep 2002, Mike Mascari wrote:
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-
-Stephan Szabo wrote:
-> On Fri, 20 Sep 2002, Mike Mascari wrote:
->>Bruce Momjian wrote:
->>>Mike Mascari wrote:
->>>>Actually, looking at the pg_pwd code, you want to determine a
->>>>way for:
->>>>
->>>>1. Process 1 opens "foo"
->>>>2. Process 2 opens "foo"
->>>>3. Process 1 creates "bar"
->>>>4. Process 1 renames "bar" to "foo"
->>>>5. Process 2 can continue to read data from the open file handle
->>>>and get the original "foo" data.
->>>
->>>
->>>Yep, that's it.
->>>
->>
->>So far, MoveFileEx("foo", "bar", MOVEFILE_REPLACE_EXISTING)
->>returns "Access Denied" when Process 1 attempts the rename. But
->>I'm continuing to investigate the possibilities...
->
->
-> Does a sequence like
-> Process 1 opens "foo"
-> Process 2 opens "foo"
-> Process 1 creates "bar"
-> Process 1 renames "foo" to <something>
-> - where something is generated to not overlap an existing file
-> Process 1 renames "bar" to "foo"
-> Process 2 continues reading
-> let you do the replace and keep reading (at the penalty that
-> you've now got to have a way to know when to remove the
-> various <something>s)
-
-Yes! Indeed that does work.
-
-Mike Mascari
-mascarm@mascari.com
-
-
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From mascarm@mascari.com Fri Sep 20 02:04:41 2002
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Stephan Szabo wrote:
> On Fri, 20 Sep 2002, Mike Mascari wrote:
mascarm@mascari.com
-From sszabo@megazone23.bigpanda.com Fri Sep 20 02:14:23 2002
-Return-path: <sszabo@megazone23.bigpanda.com>
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- for <pgman@candle.pha.pa.us>; Fri, 20 Sep 2002 02:14:21 -0400 (EDT)
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-Date: Thu, 19 Sep 2002 23:14:14 -0700 (PDT)
-From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
-To: Mike Mascari <mascarm@mascari.com>
-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-In-Reply-To: <3D8ABA3F.6030002@mascari.com>
-Message-ID: <20020919230827.A36505-100000@megazone23.bigpanda.com>
-MIME-Version: 1.0
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-
-On Fri, 20 Sep 2002, Mike Mascari wrote:
-
-> Stephan Szabo wrote:
-> > On Fri, 20 Sep 2002, Mike Mascari wrote:
-> >>So far, MoveFileEx("foo", "bar", MOVEFILE_REPLACE_EXISTING)
-> >>returns "Access Denied" when Process 1 attempts the rename. But
-> >>I'm continuing to investigate the possibilities...
-> >
-> >
-> > Does a sequence like
-> > Process 1 opens "foo"
-> > Process 2 opens "foo"
-> > Process 1 creates "bar"
-> > Process 1 renames "foo" to <something>
-> > - where something is generated to not overlap an existing file
-> > Process 1 renames "bar" to "foo"
-> > Process 2 continues reading
-> > let you do the replace and keep reading (at the penalty that
-> > you've now got to have a way to know when to remove the
-> > various <something>s)
->
-> Yes! Indeed that does work.
-
-Thinking back, I think that may still fail on Win95 (using MoveFile).
-Once in the past I had to work on (un)installers for Win* and I
-vaguely remember Win95 being more strict than Win98 but that may just
-have been with moving the executable you're currently running.
-
-
From pgsql-hackers-owner+M29185@postgresql.org Fri Sep 20 02:14:29 2002
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On Fri, 20 Sep 2002, Mike Mascari wrote:
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-Date: Fri, 20 Sep 2002 03:13:26 -0400
-From: Mike Mascari <mascarm@mascari.com>
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-To: Stephan Szabo <sszabo@megazone23.bigpanda.com>
-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
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-Stephan Szabo wrote:
-> On Fri, 20 Sep 2002, Mike Mascari wrote:
->>
->>Yes! Indeed that does work.
->
->
-> Thinking back, I think that may still fail on Win95 (using MoveFile).
-> Once in the past I had to work on (un)installers for Win* and I
-> vaguely remember Win95 being more strict than Win98 but that may just
-> have been with moving the executable you're currently running.
-
-Well, here's the test:
-
-foo.txt contains "This is FOO!"
-bar.txt contains "This is BAR!"
-
-Process 1 opens foo.txt
-Process 2 opens foo.txt
-Process 1 sleeps 7.5 seconds
-Process 2 sleeps 15 seconds
-Process 1 uses MoveFile() to rename "foo.txt" to "foo2.txt"
-Process 1 uses MoveFile() to rename "bar.txt" to "foo.txt"
-Process 1 uses DeleteFile() to remove "foo2.txt"
-Process 2 awakens and displays "This is FOO!"
-
-On the filesystem, we then have:
-
-foo.txt containing "This is BAR!"
-
-The good news is that this works fine under NT 4 using just
-MoveFile(). The bad news is that it requires the files be opened
-using CreateFile() with the FILE_SHARE_DELETE flag set. The C
-library which ships with Visual C++ 6 ultimately calls
-CreateFile() via fopen() but with no opportunity through the
-standard C library routines to use the FILE_SHARE_DELETE flag.
-And the FILE_SHARE_DELETE flag cannot be used under Windows
-95/98 (Bad Parameter). Which means, on those platforms, there
-still doesn't appear to be a solution. Under NT/XP/2K,
-AllocateFile() will have to modified to call CreateFile()
-instead of fopen(). I'm not sure about ME, but I suspect it
-behaves similarly to 95/98.
-
-Mike Mascari
-mascarm@mascari.com
-
-
-
-
-
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From mascarm@mascari.com Fri Sep 20 03:14:03 2002
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Stephan Szabo wrote:
> On Fri, 20 Sep 2002, Mike Mascari wrote:
-From tgl@sss.pgh.pa.us Fri Sep 20 10:28:40 2002
-Return-path: <tgl@sss.pgh.pa.us>
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- Fri, 20 Sep 2002 10:27:52 -0400 (EDT)
-To: Stephan Szabo <sszabo@megazone23.bigpanda.com>
-cc: Mike Mascari <mascarm@mascari.com>, Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-In-Reply-To: <20020919224718.H36366-100000@megazone23.bigpanda.com>
-References: <20020919224718.H36366-100000@megazone23.bigpanda.com>
-Comments: In-reply-to Stephan Szabo <sszabo@megazone23.bigpanda.com>
- message dated "Thu, 19 Sep 2002 22:50:36 -0700"
-Date: Fri, 20 Sep 2002 10:27:52 -0400
-Message-ID: <16067.1032532072@sss.pgh.pa.us>
-From: Tom Lane <tgl@sss.pgh.pa.us>
-Status: OR
-
-Stephan Szabo <sszabo@megazone23.bigpanda.com> writes:
-> ... let you do the replace and keep reading (at the penalty that
-> you've now got to have a way to know when to remove the
-> various <something>s)
-
-That is the hard part. Mike's description omitted one crucial step:
-
-6. The old "foo" goes away when the last open file handle for it is
-closed.
-
-I doubt there is any practical way for Postgres to cause that to happen
-if the OS itself does not have any support for it.
-
- regards, tom lane
-
From pgsql-hackers-owner+M29205@postgresql.org Fri Sep 20 10:36:48 2002
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Stephan Szabo <sszabo@megazone23.bigpanda.com> writes:
> ... let you do the replace and keep reading (at the penalty that
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I don't think we are not going to be supporting Win9X so there isn't an
> Process 1 uses DeleteFile() to remove "foo2.txt"
> Process 2 awakens and displays "This is FOO!"
>
-> On the filesystem, we then have:
->
-> foo.txt containing "This is BAR!"
->
-> The good news is that this works fine under NT 4 using just
-> MoveFile(). The bad news is that it requires the files be opened
-> using CreateFile() with the FILE_SHARE_DELETE flag set. The C
-> library which ships with Visual C++ 6 ultimately calls
-> CreateFile() via fopen() but with no opportunity through the
-> standard C library routines to use the FILE_SHARE_DELETE flag.
-> And the FILE_SHARE_DELETE flag cannot be used under Windows
-> 95/98 (Bad Parameter). Which means, on those platforms, there
-> still doesn't appear to be a solution. Under NT/XP/2K,
-> AllocateFile() will have to modified to call CreateFile()
-> instead of fopen(). I'm not sure about ME, but I suspect it
-> behaves similarly to 95/98.
->
-> Mike Mascari
-> mascarm@mascari.com
->
->
->
->
->
-> ---------------------------(end of broadcast)---------------------------
-> TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
->
-
---
- Bruce Momjian | http://candle.pha.pa.us
- pgman@candle.pha.pa.us | (610) 359-1001
- + If your life is a hard drive, | 13 Roberts Road
- + Christ can be your backup. | Newtown Square, Pennsylvania 19073
-
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-
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-
-From mascarm@mascari.com Fri Sep 20 10:57:31 2002
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-Date: Fri, 20 Sep 2002 10:57:00 -0400
-From: Mike Mascari <mascarm@mascari.com>
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-To: Bruce Momjian <pgman@candle.pha.pa.us>
-cc: Stephan Szabo <sszabo@megazone23.bigpanda.com>,
- PostgreSQL-development
- <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-References: <200209201431.g8KEVMg13344@candle.pha.pa.us>
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-
-Bruce Momjian wrote:
-> I don't think we are not going to be supporting Win9X so there isn't an
-> issue there. We will be supporting Win2000/NT/XP.
+> On the filesystem, we then have:
>
-> I don't understand FILE_SHARE_DELETE. I read the description at:
+> foo.txt containing "This is BAR!"
>
-> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/createfile.asp
+> The good news is that this works fine under NT 4 using just
+> MoveFile(). The bad news is that it requires the files be opened
+> using CreateFile() with the FILE_SHARE_DELETE flag set. The C
+> library which ships with Visual C++ 6 ultimately calls
+> CreateFile() via fopen() but with no opportunity through the
+> standard C library routines to use the FILE_SHARE_DELETE flag.
+> And the FILE_SHARE_DELETE flag cannot be used under Windows
+> 95/98 (Bad Parameter). Which means, on those platforms, there
+> still doesn't appear to be a solution. Under NT/XP/2K,
+> AllocateFile() will have to modified to call CreateFile()
+> instead of fopen(). I'm not sure about ME, but I suspect it
+> behaves similarly to 95/98.
>
-> but I don't understand it:
+> Mike Mascari
+> mascarm@mascari.com
+>
+>
+>
+>
+>
+> ---------------------------(end of broadcast)---------------------------
+> TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
>
-> FILE_SHARE_DELETE - Windows NT/2000/XP: Subsequent open operations on
-> the object will succeed only if delete access is requested.
-
-I think that's a rather poor description. I think it just means
-that if the file is opened once via CreateFile() with
-FILE_SHARE_DELETE, then any subsequent CreateFile() calls will
-fail unless they too have FILE_SHARE_DELETE. In other words, if
-one of us can delete this file while its open, any of us can.
-
-Mike Mascari
-mascarm@mascari.com
-
+--
+ Bruce Momjian | http://candle.pha.pa.us
+ pgman@candle.pha.pa.us | (610) 359-1001
+ + If your life is a hard drive, | 13 Roberts Road
+ + Christ can be your backup. | Newtown Square, Pennsylvania 19073
+---------------------------(end of broadcast)---------------------------
+TIP 6: Have you searched our list archives?
+http://archives.postgresql.org
From pgsql-hackers-owner+M29208@postgresql.org Fri Sep 20 11:30:26 2002
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Bruce Momjian wrote:
> I don't think we are not going to be supporting Win9X so there isn't an
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Mike Mascari wrote:
> Bruce Momjian wrote:
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-Date: Fri, 20 Sep 2002 08:10:19 -0700 (PDT)
-From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
-To: Mike Mascari <mascarm@mascari.com>
-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-In-Reply-To: <3D8B373C.7060102@mascari.com>
-Message-ID: <20020920080949.H40440-100000@megazone23.bigpanda.com>
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-
-On Fri, 20 Sep 2002, Mike Mascari wrote:
-
-> Bruce Momjian wrote:
-> > I don't think we are not going to be supporting Win9X so there isn't an
-> > issue there. We will be supporting Win2000/NT/XP.
-> >
-> > I don't understand FILE_SHARE_DELETE. I read the description at:
-> >
-> > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/createfile.asp
-> >
-> > but I don't understand it:
-> >
-> > FILE_SHARE_DELETE - Windows NT/2000/XP: Subsequent open operations on
-> > the object will succeed only if delete access is requested.
->
-> I think that's a rather poor description. I think it just means
-> that if the file is opened once via CreateFile() with
-> FILE_SHARE_DELETE, then any subsequent CreateFile() calls will
-> fail unless they too have FILE_SHARE_DELETE. In other words, if
-> one of us can delete this file while its open, any of us can.
-
-The question is, what happens if two people have the file open
-and one goes and tries to delete it? Can the other still read
-from it?
-
-
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From sszabo@megazone23.bigpanda.com Fri Sep 20 11:29:09 2002
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On Fri, 20 Sep 2002, Mike Mascari wrote:
from it?
-From JanWieck@Yahoo.com Fri Sep 20 11:36:53 2002
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- PostgreSQL-development <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
-References: <20020919230827.A36505-100000@megazone23.bigpanda.com> <3D8ACA96.80504@mascari.com>
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-Mike Mascari wrote:
-
-> instead of fopen(). I'm not sure about ME, but I suspect it
-> behaves similarly to 95/98.
-
-I just checked with Katie and the good news (tm) is that the Win32 port
-we did here at PeerDirect doesn't support 95/98 and ME anyway. It does
-support NT4, 2000 and XP. So don't bother.
-
-
-Jan
-
---
-
-#======================================================================#
-# It's easier to get forgiveness for being wrong than for being right. #
-# Let's break this rule - forgive me. #
-#================================================== JanWieck@Yahoo.com #
-
From pgsql-hackers-owner+M29216@postgresql.org Fri Sep 20 11:45:47 2002
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Mike Mascari wrote:
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Stephan Szabo wrote:
> On Fri, 20 Sep 2002, Mike Mascari wrote:
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-Date: Fri, 20 Sep 2002 11:54:52 -0400
-From: Mike Mascari <mascarm@mascari.com>
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-To: Stephan Szabo <sszabo@megazone23.bigpanda.com>
-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL-development
- <pgsql-hackers@postgresql.org>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
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-Stephan Szabo wrote:
-> On Fri, 20 Sep 2002, Mike Mascari wrote:
->
->
->>I think that's a rather poor description. I think it just means
->>that if the file is opened once via CreateFile() with
->>FILE_SHARE_DELETE, then any subsequent CreateFile() calls will
->>fail unless they too have FILE_SHARE_DELETE. In other words, if
->>one of us can delete this file while its open, any of us can.
->
->
-> The question is, what happens if two people have the file open
-> and one goes and tries to delete it? Can the other still read
-> from it?
-
-Yes. I just tested it and it worked. I'll test Bruce's scenario
-as well:
-
-foo contains: "FOO"
-bar contains: "BAR"
-
-1. Process 1 opens "foo"
-2. Process 2 opens "foo"
-3. Process 1 calls MoveFile("foo", "foo2");
-4. Process 3 opens "foo" <- Successful?
-5. Process 1 calls MoveFile("bar", "foo");
-6. Process 4 opens "foo" <- Successful?
-7. Process 1 calls DeleteFile("foo2");
-8. Process 1, 2, 3, 4 all read from their respective handles.
-
-I think the thing to worry about is a race condition between the
-two MoveFile() attempts. A very ugly hack would be to loop in a
-CreateFile() in an attempt to open "foo", giving up if the error
-is not a NOT EXISTS error code.
-
-Mike Mascari
-mascarm@mascari.com
-
-
-From mascarm@mascari.com Fri Sep 20 12:29:18 2002
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-Date: Fri, 20 Sep 2002 12:27:32 -0400
-From: Mike Mascari <mascarm@mascari.com>
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-To: PostgreSQL-development <pgsql-hackers@postgresql.org>
-cc: Stephan Szabo <sszabo@megazone23.bigpanda.com>,
- Bruce Momjian
- <pgman@candle.pha.pa.us>
-Subject: Re: [HACKERS] Win32 rename()/unlink() questions
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-I wrote:
-> Stephan Szabo wrote:
- >>
->> The question is, what happens if two people have the file open
->> and one goes and tries to delete it? Can the other still read
->> from it?
->
-> Yes. I just tested it and it worked. I'll test Bruce's scenario as well:
->
-> foo contains: "FOO"
-> bar contains: "BAR"
->
-> 1. Process 1 opens "foo"
-> 2. Process 2 opens "foo"
-> 3. Process 1 calls MoveFile("foo", "foo2");
-> 4. Process 3 opens "foo" <- Successful?
-> 5. Process 1 calls MoveFile("bar", "foo");
-> 6. Process 4 opens "foo" <- Successful?
-> 7. Process 1 calls DeleteFile("foo2");
-> 8. Process 1, 2, 3, 4 all read from their respective handles.
-
-Process 1: "FOO"
-Process 2: "FOO"
-Process 3: Error - File does not exist
-Process 4: "BAR"
-
-Its interesting in that it allows for Unix-style rename() and
-unlink() behavior, but with a race condition. Without Stephan's
-two MoveFile() trick and the FILE_SHARE_DELETE flag, however,
-the result would be Access Denied. Are the places in the backend
-that use rename() and unlink() renaming and unlinking files that
-are only opened for a brief moment by other backends?
-
-Mike Mascari
-mascarm@mascari.com
-
-
From pgsql-hackers-owner+M29230@postgresql.org Fri Sep 20 13:12:45 2002
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I wrote:
> Stephan Szabo wrote:
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Mike Mascari wrote:
> Its interesting in that it allows for Unix-style rename() and
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Mike Mascari wrote:
> > foo contains: "FOO"
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It is good that moving the file out of the way works, but it doesn't
Date: Fri, 20 Sep 2002 11:50:17 -0400
Message-ID: <16739.1032537017@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I think we may be best just looping on MoveFileEx() until is succeeds.
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Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
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