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From David Van Couvering <da...@vancouvering.com>
Subject Re: Database corruption on crash during table creation
Date Tue, 06 Jul 2010 15:42:13 GMT
On Mon, Jul 5, 2010 at 11:52 PM, Kristian Waagan <Kristian.Waagan@sun.com>wrote:

> On 06.07.10 08:23, David Van Couvering wrote:
>
>> Hi, all.  I seem to have a repeatable issue where my database is getting
>> corrupted, and I can only assume it's happening when the table is getting
>> created, because I know Derby is great on handling crashes during normal
>> operation.
>>
>> First of all - is it true that a Derby database can get corrupted if the
>> VM goes down in the middle of a DML like CREATE TABLE?
>>
>> What I'm seeing is that upon restart, when I try to access the database, I
>> get the error "unable to create database FOO: the directory already exists."
>>  The directory contains what appears to be a Derby database, but apparently
>> not enough of one.
>>
>
> Hi David,
>
> It would be great if you can create a Jira and attach the contents of the
> database directory (or maybe just the output from find). Including a
> runnable repro would be even better :)
>

I'll see what I can do - the error was reported by another developer and I
don't know if he kept his environment around.


> Also:
>  o Can the issue be reproduced using ij only?
>

No, this happens using JDBC


>  o Is this reproducible when only a single process is accessing/modifying
> the database?
>
>
Yes, this is single process, even single-threaded (I am funneling all Derby
requests to a given database through a single thread).


> I believe there has been a few reports of the error message you mentioned,
> but so far no repro has been available.
>
> Having a forceCreate option requires some thought, it would be unfortunate
> if Derby deleted (i.e. misuse or exploit) a bunch of user/system files. This
> wouldn't be such a big deal if everyone tightened the Java security policy
> for Derby, but I'm not sure that's the case...
>
> Yes, I can see this being an issue...

If you have clarity on what you want here, e.g. do you *want* a forceCreate,
I might consider doing it in the engine.  Of course I'd have to go through
legal to even be allowed to contribute as a Symantec employee :)

David

>
> Regards,
> --
> Kristian
>
>
>
>> What I'm hoping for, is there a "forceCreate=true" kind of option when
>> opening a database that forces the creation of the database in the given
>> directory even if something is already there?
>>
>> Otherwise it appears my only option is to detect this specific error
>> ('directory already exists'), and then blow away what's there and try again.
>>  That's a chunk of work I'd rather not do, so I'm hoping you've already
>> addressed it (ahem :)).
>>
>> Thanks,
>>
>> David
>>
>> --
>> David W. Van Couvering
>>
>> http://www.linkedin.com/in/davidvc
>> http://davidvancouvering.blogspot.com
>> http://twitter.com/dcouvering
>>
>
>


-- 
David W. Van Couvering

http://www.linkedin.com/in/davidvc
http://davidvancouvering.blogspot.com
http://twitter.com/dcouvering

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