DBCC CHECKDB explanation

Hello All,
I ran DBCC CHECKDB('myDatabase'). After
scanning all the tables it finally gave this message:
CHECKDB found 0 allocation errors and 0 consistency errors
in database 'myDatabase'.
DBCC execution completed. If DBCC printed error messages,
contact your system administrator.
Can anyone tell me what does it mean by allocation errors
and consistency errors? Actually I am preparing for MCDBA
exams and I wanted to understand the concepts fully.
Thanks in advance
AnandExample of allocation error:
The allocation structure (IAM page) states that object X uses page Y. SQL Server goes to page Y and
the page header states that page Y is owned by object Z!
Example of consistency error:
SQL Server follows a linked list for an index and when coming to a page it sees that the previous
page in that page header is not the same as the page where it came from.
--
Tibor Karaszi, SQL Server MVP
Archive at: http://groups.google.com/groups?oi=djq&as ugroup=microsoft.public.sqlserver
"Anand" <anand_r@.linuxmail.org> wrote in message news:118201c39237$75ab6810$a101280a@.phx.gbl...
> Hello All,
> I ran DBCC CHECKDB('myDatabase'). After
> scanning all the tables it finally gave this message:
> CHECKDB found 0 allocation errors and 0 consistency errors
> in database 'myDatabase'.
> DBCC execution completed. If DBCC printed error messages,
> contact your system administrator.
>
> Can anyone tell me what does it mean by allocation errors
> and consistency errors? Actually I am preparing for MCDBA
> exams and I wanted to understand the concepts fully.
> Thanks in advance
> Anand
>|||Thanks Tibor,
By the way when does this happen?
Regards
Anand
>--Original Message--
>Example of allocation error:
>The allocation structure (IAM page) states that object X
uses page Y. SQL Server goes to page Y and
>the page header states that page Y is owned by object Z!
>
>Example of consistency error:
>SQL Server follows a linked list for an index and when
coming to a page it sees that the previous
>page in that page header is not the same as the page
where it came from.
>--
>Tibor Karaszi, SQL Server MVP
>Archive at: http://groups.google.com/groups?oi=djq&as
ugroup=microsoft.public.sqlserver
>
>"Anand" <anand_r@.linuxmail.org> wrote in message
news:118201c39237$75ab6810$a101280a@.phx.gbl...
>> Hello All,
>> I ran DBCC CHECKDB('myDatabase'). After
>> scanning all the tables it finally gave this message:
>> CHECKDB found 0 allocation errors and 0 consistency
errors
>> in database 'myDatabase'.
>> DBCC execution completed. If DBCC printed error
messages,
>> contact your system administrator.
>>
>> Can anyone tell me what does it mean by allocation
errors
>> and consistency errors? Actually I am preparing for
MCDBA
>> exams and I wanted to understand the concepts fully.
>> Thanks in advance
>> Anand
>>
>
>.
>|||Theoretically it can be bug in SQL Server, writing the incorrect bits to disk. I don't know if any
such problems has appeared since 6.5. So, in practice, we are talking about HW problems, HW write
caching without battery backup and such things.
--
Tibor Karaszi, SQL Server MVP
Archive at: http://groups.google.com/groups?oi=djq&as ugroup=microsoft.public.sqlserver
"Anand" <anand_r@.linuxmail.org> wrote in message news:2a51e01c3923c$54b99f50$a601280a@.phx.gbl...
> Thanks Tibor,
> By the way when does this happen?
> Regards
> Anand
>
> >--Original Message--
> >Example of allocation error:
> >
> >The allocation structure (IAM page) states that object X
> uses page Y. SQL Server goes to page Y and
> >the page header states that page Y is owned by object Z!
> >
> >
> >Example of consistency error:
> >SQL Server follows a linked list for an index and when
> coming to a page it sees that the previous
> >page in that page header is not the same as the page
> where it came from.
> >
> >--
> >Tibor Karaszi, SQL Server MVP
> >Archive at: http://groups.google.com/groups?oi=djq&as
> ugroup=microsoft.public.sqlserver
> >
> >
> >"Anand" <anand_r@.linuxmail.org> wrote in message
> news:118201c39237$75ab6810$a101280a@.phx.gbl...
> >> Hello All,
> >> I ran DBCC CHECKDB('myDatabase'). After
> >> scanning all the tables it finally gave this message:
> >>
> >> CHECKDB found 0 allocation errors and 0 consistency
> errors
> >> in database 'myDatabase'.
> >> DBCC execution completed. If DBCC printed error
> messages,
> >> contact your system administrator.
> >>
> >>
> >> Can anyone tell me what does it mean by allocation
> errors
> >> and consistency errors? Actually I am preparing for
> MCDBA
> >> exams and I wanted to understand the concepts fully.
> >>
> >> Thanks in advance
> >> Anand
> >>
> >>
> >
> >
> >.
> >|||Thanks Tibor,
Do you have any reference url which can throw more
light on such things.
Regards
Anand
>--Original Message--
>Theoretically it can be bug in SQL Server, writing the
incorrect bits to disk. I don't know if any
>such problems has appeared since 6.5. So, in practice, we
are talking about HW problems, HW write
>caching without battery backup and such things.
>--
>Tibor Karaszi, SQL Server MVP
>Archive at: http://groups.google.com/groups?oi=djq&as
ugroup=microsoft.public.sqlserver
>
>"Anand" <anand_r@.linuxmail.org> wrote in message
news:2a51e01c3923c$54b99f50$a601280a@.phx.gbl...
>> Thanks Tibor,
>> By the way when does this happen?
>> Regards
>> Anand
>>
>> >--Original Message--
>> >Example of allocation error:
>> >
>> >The allocation structure (IAM page) states that object
X
>> uses page Y. SQL Server goes to page Y and
>> >the page header states that page Y is owned by object
Z!
>> >
>> >
>> >Example of consistency error:
>> >SQL Server follows a linked list for an index and when
>> coming to a page it sees that the previous
>> >page in that page header is not the same as the page
>> where it came from.
>> >
>> >--
>> >Tibor Karaszi, SQL Server MVP
>> >Archive at: http://groups.google.com/groups?oi=djq&as
>> ugroup=microsoft.public.sqlserver
>> >
>> >
>> >"Anand" <anand_r@.linuxmail.org> wrote in message
>> news:118201c39237$75ab6810$a101280a@.phx.gbl...
>> >> Hello All,
>> >> I ran DBCC CHECKDB('myDatabase'). After
>> >> scanning all the tables it finally gave this message:
>> >>
>> >> CHECKDB found 0 allocation errors and 0 consistency
>> errors
>> >> in database 'myDatabase'.
>> >> DBCC execution completed. If DBCC printed error
>> messages,
>> >> contact your system administrator.
>> >>
>> >>
>> >> Can anyone tell me what does it mean by allocation
>> errors
>> >> and consistency errors? Actually I am preparing for
>> MCDBA
>> >> exams and I wanted to understand the concepts fully.
>> >>
>> >> Thanks in advance
>> >> Anand
>> >>
>> >>
>> >
>> >
>> >.
>> >
>
>.
>|||I'm sure that there exists web sites with such info, but I haven't searched for such myself. I'm
sure that you find such by doing a bit of web-searching.
--
Tibor Karaszi, SQL Server MVP
Archive at: http://groups.google.com/groups?oi=djq&as ugroup=microsoft.public.sqlserver
"Anand" <anand_r@.linuxmail.org> wrote in message news:0f6301c3923e$aeacbe50$a301280a@.phx.gbl...
> Thanks Tibor,
> Do you have any reference url which can throw more
> light on such things.
> Regards
> Anand
> >--Original Message--
> >Theoretically it can be bug in SQL Server, writing the
> incorrect bits to disk. I don't know if any
> >such problems has appeared since 6.5. So, in practice, we
> are talking about HW problems, HW write
> >caching without battery backup and such things.
> >
> >--
> >Tibor Karaszi, SQL Server MVP
> >Archive at: http://groups.google.com/groups?oi=djq&as
> ugroup=microsoft.public.sqlserver
> >
> >
> >"Anand" <anand_r@.linuxmail.org> wrote in message
> news:2a51e01c3923c$54b99f50$a601280a@.phx.gbl...
> >> Thanks Tibor,
> >> By the way when does this happen?
> >>
> >> Regards
> >> Anand
> >>
> >>
> >> >--Original Message--
> >> >Example of allocation error:
> >> >
> >> >The allocation structure (IAM page) states that object
> X
> >> uses page Y. SQL Server goes to page Y and
> >> >the page header states that page Y is owned by object
> Z!
> >> >
> >> >
> >> >Example of consistency error:
> >> >SQL Server follows a linked list for an index and when
> >> coming to a page it sees that the previous
> >> >page in that page header is not the same as the page
> >> where it came from.
> >> >
> >> >--
> >> >Tibor Karaszi, SQL Server MVP
> >> >Archive at: http://groups.google.com/groups?oi=djq&as
> >> ugroup=microsoft.public.sqlserver
> >> >
> >> >
> >> >"Anand" <anand_r@.linuxmail.org> wrote in message
> >> news:118201c39237$75ab6810$a101280a@.phx.gbl...
> >> >> Hello All,
> >> >> I ran DBCC CHECKDB('myDatabase'). After
> >> >> scanning all the tables it finally gave this message:
> >> >>
> >> >> CHECKDB found 0 allocation errors and 0 consistency
> >> errors
> >> >> in database 'myDatabase'.
> >> >> DBCC execution completed. If DBCC printed error
> >> messages,
> >> >> contact your system administrator.
> >> >>
> >> >>
> >> >> Can anyone tell me what does it mean by allocation
> >> errors
> >> >> and consistency errors? Actually I am preparing for
> >> MCDBA
> >> >> exams and I wanted to understand the concepts fully.
> >> >>
> >> >> Thanks in advance
> >> >> Anand
> >> >>
> >> >>
> >> >
> >> >
> >> >.
> >> >
> >
> >
> >.
> >