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On Thu, 20 Jun 2002, Bruce Momjian wrote:
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On Fri, 21 Jun 2002, Tom Lane wrote:
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On Thu, 2002-06-20 at 21:58, Bruce Momjian wrote:
> I was wondering, how does knowing the block is corrupt help MS SQL?
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On Sat, 2002-06-22 at 19:17, Bruce Momjian wrote:
> J. R. Nield wrote:
http://archives.postgresql.org
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-Subject: Re: [HACKERS] Index Scans become Seq Scans after VACUUM ANALYSE
- mlw
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-On Sat, 2002-06-22 at 19:17, Bruce Momjian wrote:
-> J. R. Nield wrote:
-> > One other point:
-> >
-> > Page pre-image logging is fundamentally the same as what Jim Grey's
-> > book[1] would call "careful writes". I don't believe they should be in
-> > the XLOG, because we never need to keep the pre-images after we're sure
-> > the buffer has made it to the disk. Instead, we should have the buffer
-> > IO routines implement ping-pong writes of some kind if we want
-> > protection from partial writes.
->
-> Ping-pong writes to where? We have to fsync, and rather than fsync that
-> area and WAL, we just do WAL. Not sure about a win there.
->
-
-The key question is: do we have some method to ensure that the OS
-doesn't do the writes in parallel?
-
-If the OS will ensure that one of the two block writes of a ping-pong
-completes before the other starts, then we don't need to fsync() at
-all.
-
-The only thing we are protecting against is the possibility of both
-writes being partial. If neither is done, that's fine because WAL will
-protect us. If the first write is partial, we will detect that and use
-the old data from the other, then recover from WAL. If the first is
-complete but the second is partial, then we detect that and use the
-newer block from the first write. If the second is complete but the
-first is partial, we detect that and use the newer block from the second
-write.
-
-So does anyone know a way to prevent parallel writes in one of the
-common unix standards? Do they say anything about this?
-
-It would seem to me that if the same process does both ping-pong writes,
-then there should be a cheap way to enforce a serial order. I could be
-wrong though.
-
-As to where the first block of the ping-pong should go, maybe we could
-reserve a file with nBlocks space for them, and write the information
-about which block was being written to the XLOG for use in recovery.
-There are many other ways to do it.
-
-;jrnield
-
---
-J. R. Nield
-
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On 23 Jun 2002, J. R. Nield wrote:
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> This should also allow us to disable completely the ping-pong writes
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On Sun, 23 Jun 2002, Tom Lane wrote:
Date: 23 Jun 2002 13:57:19 -0400
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On Sun, 2002-06-23 at 11:19, Tom Lane wrote:
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On 23 Jun 2002, J. R. Nield wrote:
Date: 23 Jun 2002 14:15:17 -0400
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On Sun, 2002-06-23 at 12:10, Curt Sampson wrote:
>
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J. R. Nield wrote:
> So since we have all this buffering designed especially to meet our
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Curt Sampson wrote:
> On 23 Jun 2002, J. R. Nield wrote:
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On Sun, 23 Jun 2002, Bruce Momjian wrote:
Date: 23 Jun 2002 21:29:23 -0400
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On Sun, 2002-06-23 at 15:36, Bruce Momjian wrote:
> Yes, I don't see writing to two files vs. one to be any win, especially
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J. R. Nield wrote:
> On Sun, 2002-06-23 at 15:36, Bruce Momjian wrote:
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On 23 Jun 2002, J. R. Nield wrote:
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> On Sun, 23 Jun 2002, Bruce Momjian wrote:
>> Yes, I don't see writing to two files vs. one to be any win, especially
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Tom Lane wrote:
> > On Sun, 23 Jun 2002, Bruce Momjian wrote:
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>> The only thing I've been able to think of that seems like it might
Date: 24 Jun 2002 16:49:42 -0400
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On Sun, 2002-06-23 at 23:40, Curt Sampson wrote:
> On 23 Jun 2002, J. R. Nield wrote:
Date: Mon, 24 Jun 2002 17:16:01 -0400
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> Also, postgreSQL can't recover from any other type of block corruption,
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J. R. Nield wrote:
> > This I don't quite understand. Assuming you're using a SCSI drive
Date: Mon, 24 Jun 2002 17:31:56 -0400
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>> Does anyone know what the major barriers to infinite log replay are in
regards, tom lane
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-Subject: Re: [HACKERS] Index Scans become Seq Scans after VACUUM ANALYSE
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->> Does anyone know what the major barriers to infinite log replay are in
->> PostgreSQL? I'm trying to look for everything that might need to be
->> changed outside xlog.c, but surely this has come up before. Searching
->> the archives hasn't revealed much.
-
-> This has been brought up. Could we just save WAL files and get replay?
-> I believe some things have to be added to WAL to allow this, but it
-> seems possible.
-
-The Red Hat group has been looking at this somewhat; so far there seem
-to be some minor tweaks that would be needed, but no showstoppers.
-
-> Somehow you would need a tar-type
-> backup of the database, and with a running db, it is hard to get a valid
-> snapshot of that.
-
-But you don't *need* a "valid snapshot", only a correct copy of
-every block older than the first checkpoint in your WAL log series.
-Any inconsistencies in your tar dump will look like repairable damage;
-replaying the WAL log will fix 'em.
-
- regards, tom lane
-
-
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Tom Lane wrote:
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-Subject: Re: [HACKERS] Index Scans become Seq Scans after VACUUM ANALYSE
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-On Mon, 2002-06-24 at 17:16, Tom Lane wrote:
-
-> I think you have been missing the point...
-Yes, this appears to be the case. Thanks especially to Curt for clearing
-things up for me.
-
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-J. R. Nield
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Date: 24 Jun 2002 20:28:00 -0400
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On Mon, 2002-06-24 at 17:16, Tom Lane wrote:
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On 24 Jun 2002, J. R. Nield wrote:
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On Mon, 24 Jun 2002, Tom Lane wrote:
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Curt Sampson wrote:
> On Mon, 24 Jun 2002, Tom Lane wrote:
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I have been experimenting with empirical tests of file system and device
level writes to determine the actual constraints in order to speed up the WAL
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> One of the things I was thinking about was whether we could use up those
projects / users / bernd / postgres.git / commitdiff