Subject RE: [firebird-support] Firebird Embedded corruptions
Author Marcos Herrera
Hi Dear Friends

I could resolve the issue, I copied the DLL in my machine and create an
alias in aliases.conf

Thanks for all



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*De:* [mailto:]
*Enviado el:* martes, 23 de septiembre de 2014 09:50 a.m.
*Asunto:* Re: [firebird-support] Firebird Embedded corruptions


Thanks for this and sorry for my slow response. Please see my comments

Best Regards

//Jan Flyborg

2014-09-19 21:13 GMT+02:00 Ann Harrison aharrison@...
[firebird-support] <>:

On Mon, Sep 15, 2014 at 7:41 AM, Jan Flyborg jan.persson@...
[firebird-support] <> wrote:

I just made another posting where I tried to describe three different
examples of things we have seen.

The first was a wrong page type, which sounds like a bug that was fixed in
a newer version in code that's common to all Firebird architectures. In
your case, the bad page was in an index (7). If you can find the index
with the bad page and recreate it, all will be well.

Just as an FYI, the page types are:

0 - undefined, normally an uninitialized page and indicates a
bad page pointer elsewhere;

1 - Database header page

2 - Page inventory page

3 - Transaction inventory page

4 - Pointer page

5 - Data page

6 - Index root page - contains information about each index on the
table, one per table

7 - Index (B-tree) page

8 - Blob data page

9 - Generator pages

That sounds very good and it seems like an upgrade to 2.5.3 will make sure
that we do not see this again.

The second problem (CCH_precedence: block marked. file: cch.cpp line:
4390) is more concerning - I don't remember having read a bug about it.
CCH is the cache handler. A "mark" is the sign that a page is about to be
changed. When Firebird is forced to write a page either as part of a
commit or to free space in the cache, it must write out any pages that the
page depends on first. That's a little obscure. Suppose that the page
you're about to write has a record with a back version, and the back
version is on a different page. To keep the database consistent, the page
with the back version must be on disk before the page that includes a
record that points to the back version. Firebird keeps a list of
precedence relationships and CCH goes through them before writing a page.
I think the error means that someone is currently writing to a page that's
on the precedence list. That should never happen. It's interesting that
the problem occurred during an alter index operation. However, the
database should be fine on disk and usable after you restart Firebird.
Page marks are entirely in memory. It's quite possible that I missed a bug
report and this problem was fixed in a later version.

If that is of any help for you, I was wrong in my original posting when I
said we were using 2.5.1 (I mean that the line numbers in the exception
might lead you to draw the wrong conclusion when I gave you the wrong
version). We are currently using 2.5.2 and nothing else.

The third problem is two records in a referencing table lack mates in the
referenced table, despite a referential constraint. I have no idea how
that happened, but it should be reasonably easy to fix in your database.

In another posting (later than yours) Fabiano is saying that these errors
are connected to bad memory chips and in the future we will instruct our
users who are having this problem to run memtest86 overnight to check that
the memory is physically OK. These constraints problems are actually the
most common that we see.

The first problem is what I would call a physical corruption - the
internal structure of the database is corrupt. The second is an in-memory
corruption - the disk database is OK, but the in-memory version is
damaged. The third is logical corruption - the database is physically
intact, but does not conform to the data rules..

Typically we fix our problems with a gfix -mend and then doing a backup
restore cycle. Usually some tables then still have problems (typically
foreign keys that refers to non existing primary keys), so if possible we
then remove the faulty records and then it works again.

Problem is that these are not my databases. I have normally no access to
them since they are running in a standalone installation at our customers
sites. Recently we have bundled our own homemade tool for repairing
databases that our customer can use when they are experiencing problems
(basically a graphical frontend for gfix), but sometimes this is not enough
and the databases has to be sent to us.

Gfix is pretty old and somewhat crude. IBFirstAid might give you better
help on physical corruptions. Checking that there is no non-conforming
data before creating constraints may help with logical corruption.

Yes that would probably be a better choice for us, but we cannot bundle
IBFirstAId together with our application. Will however download it and try
it on files to got sent to us.

Good luck (and my apologies for the late response)

No need for any apologies. I am very grateful for you taking your time to
help us.

Another thing, what do you say about the posting above where the theory is
that Volume Shadow Copy is interfering with the database? Have you heard
about that before?

And another last comment. We have bundled Firebird with very many
installations of our product and it might be the case that what we are
seeing are very rare problems, that no one else has experienced before. Do
you think we should post bug reports every time we see an exception or a
problem that you have not already been made aware of? I mean the second
problem in my list was new to you.


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