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dbcc error 806 with page 538976256

3 posts in General Discussion Last posting was on 2010-01-19 16:37:12.0Z
John Flynn Posted on 2010-01-18 20:48:55.0Z
From: "John Flynn" <jflynn@miqs.com>
Newsgroups: sybase.public.ase.general
Subject: dbcc error 806 with page 538976256
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Hi.

Within the past week I've had six separate occurrences of a particular dbcc
tablealloc error, on five different ASE servers. They all have something in
common, they are all on logical page 538976256. They look like this:

Msg 806, Level 16, State 1:
Line 1:
Could not find virtual page for logical page 538976256 in database 'xyz'.

My dbcc's run once a week. In one particular database, the error happened
one week on one table, then the next week it happened on a different table.
The same day, it happened on four completely different databases (on four
different physical machines). But they all shared the logical page number of
538976256.

This seems extremely weird to me. Is there something special about that page
number? Since I personally installed all those servers, could I have done
something wrong the same way every time? Or, does this smell like an ASE
bug? Does anyone know anything about this? My servers are all on ASE 15.0.2
ESD #6.

Thanks.
- John.


Bret Halford Posted on 2010-01-18 23:03:30.0Z
From: Bret Halford <bret@sybase.com>
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Subject: Re: dbcc error 806 with page 538976256
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On 1/18/2010 1:48 PM, John Flynn wrote:
> Hi.
>
> Within the past week I've had six separate occurrences of a particular dbcc
> tablealloc error, on five different ASE servers. They all have something in
> common, they are all on logical page 538976256. They look like this:
>
> Msg 806, Level 16, State 1:
> Line 1:
> Could not find virtual page for logical page 538976256 in database 'xyz'.
>
> My dbcc's run once a week. In one particular database, the error happened
> one week on one table, then the next week it happened on a different table.
> The same day, it happened on four completely different databases (on four
> different physical machines). But they all shared the logical page number of
> 538976256.
>
> This seems extremely weird to me. Is there something special about that page
> number? Since I personally installed all those servers, could I have done
> something wrong the same way every time? Or, does this smell like an ASE
> bug? Does anyone know anything about this? My servers are all on ASE 15.0.2
> ESD #6.
>
> Thanks.
> - John.

Hi John,

538976256 decimal is 0x20202000 hex, which is a somewhat more
interesting value than your average random value.

The first thought that comes to mind is that 0x20 is an ASCII space, so
I might suspect something like a null-terminated string of spaces is
overwriting the page number somewhere, somehow.

When I search our infobase for this number, I do get one known CR
543053 that was for checkalloc with fix hitting error 806
with this number. The details of the bug indicate it was due to
a new variable in the code that in some cases wasn't initialized.
It isn't clear to me why the value wouldn't be more random, but
the test case showed the same value popping up several times. So I
think it is fairly likely you are hitting this CR.

CR 543053 is fixed in 15.03 ESD #1. I recommend applying the current
15.0.3 rollup or 15.5.

Cheers,
-bret


John Flynn Posted on 2010-01-19 16:37:12.0Z
From: "John Flynn" <jflynn@miqs.com>
Newsgroups: sybase.public.ase.general
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Bret Halford wrote:
> 538976256 decimal is 0x20202000 hex, which is a somewhat more
> interesting value than your average random value.
>
> The first thought that comes to mind is that 0x20 is an ASCII space,
> so I might suspect something like a null-terminated string of spaces
> is overwriting the page number somewhere, somehow.

Yes, I noticed that too. At first I assumed it was probably equal to "the
number of pages allocated to my database", which might plausibly be a
"semi-round" number (since I tend to like nice even powers-of-two). But that
didn't seem to pan out mathematically. The thing with the spaces never even
occurred to me.

> When I search our infobase for this number, I do get one known CR
> 543053 that was for checkalloc with fix hitting error 806
> with this number. The details of the bug indicate it was due to
> a new variable in the code that in some cases wasn't initialized.
> It isn't clear to me why the value wouldn't be more random, but
> the test case showed the same value popping up several times. So I
> think it is fairly likely you are hitting this CR.

The most puzzling thing is why this has popped up in 5 of my servers all in
the same week. These servers have all been stabilized on the same ASE
release for several months. It's as if the glitch is date-related.

> CR 543053 is fixed in 15.03 ESD #1. I recommend applying the current
> 15.0.3 rollup or 15.5.

Thanks very much, that sounds like a great idea.

- John.