Re: McKoi db error

[Geert Bevin <gbevin at uwyn dot com>]

Hi Tom,

thanks for the info.

> I don't know what the McKoi db is, but cool.

McKoi db is a similar db to Hsql except that it strives for SQL92 
completeness and usage in a server invironment as well as for embedded. 
It's supposed to perform quite well in both areas.

> The error message in question comes from java.io.ObjectInputStream.
> Unfortunately for you, our serialization support isn't as well-tested
> as other parts of libgcj.  So you've probably run into a serialization
> bug of some kind.
>
> The only real option is to debug the library and find out what has
> gone wrong.

I also contacted the McKoi developers and they gave me some pointers 
where the start looking. I thus spent the entire day tracing this 
problem and I found a solution and an additional problem. First of all I 
think both McKoi and gcj are at fault. The Serializable interface 
documents that when the serialization requires special handling both the 
readObject and writeObject methods should be implemented. Apparently 
most jdk implementation provide the default implementation if either one 
isn't implemented, but gcj apparently takes the other route. When adding 
the following method to the Expression and TObject classes of McKoi db, 
the initial problem disappears.

private void writeObject(java.io.ObjectOutputStream out)
throws IOException
{
    out.defaultWriteObject();
}

These errors occur during the creation of the initial structure of the 
database and more specifically during the creation of the views. This 
procedure continues now quite a bit further than before, but I 
encountered a similar error. At first I thought it was the same issue 
but now I'm doubting. Again I get the following error :

read view plan
> com.mckoi.database.Database ( lvl: 40 )
  java.lang.Error: IO Error: Unknown marker on stream: 0
   at 
com.mckoi.database.ViewDef.deserializeFromBlob(com.mckoi.database.global.ByteLongObject) 
(/home/gbevin/mckoi-sql/src/lib-com-mckoi.so)
   at com.mckoi.database.DatabaseConnection.getViewDef(int) 
(/home/gbevin/mckoi-sql/src/lib-com-mckoi.so)
   at 
com.mckoi.database.DatabaseConnection$ViewInternalTableInfo.getDataTableDef(int) 
(/home/gbevin/mckoi-sql/src/lib-com-mckoi.so)
 ...

But, after hours of searching I couldn't replicate the problem in 
memory. Then I decided to check what the bytes are that are available 
after serialization and what the ones are that are available for 
deserialization. I came to the constatation that they are very 
different. In fact after 109 bytes, the rest of the byte array that is 
provided to the deserialization method is filled with bytes that are 
equal to 0! Therefore it's of course impossible to deserialize correctly.
Is there something known about the IO of the current 3.3 branch? I find 
this a very strange problem and am a bit lost when thinking about how to 
find a solution. I also asked the McKoi developers for additional help.

Any pointers are very appreciated !

Thanks for the help,

Geert

--
Geert Bevin             Uwyn
"Use what you need"     Lambermontlaan 148
http://www.uwyn.com     1030 Brussels
gbevin at uwyn dot com         Tel & Fax +32 2 245 41 06

PGP Fingerprint : 4E21 6399 CD9E A384 6619  719A C8F4 D40D 309F D6A9
Public PGP key  : available at servers pgp.mit.edu, wwwkeys.pgp.net