Re: Question about softupgrade mode ..

[TomohitoNakayama <to...@basil.ocn.ne.jp>]

Hello.

Daniel John Debrunner wrote:

> I think your proposal should be modified a little and take advantage of
> the current implementation of DefaultInfoImpl.
> 
> 1) Continue to store NULL in the COLUMNDEFAULT column of SYSCOLUMNS for
> GENERATED ALWAYS, means there is no default option. This makes sense,
> this column is not applicable for GENERATED ALWAYS
> 
> 2) For GENERATED BY DEFAULT store a non-NULL value in the COLUMNDEFAULT
> column of SYSCOLUMNS, using the an instance of the DefaultInfoImpl
> class. This class has a spare field in its stored format that is
> currently always zero, this is very useful to add meaning or
> functionality to its stored form. So I would propose
> 
>    - existing defaults continue as they are, the extra field becomes
>     a status field and a value of zero means a regular default.
> 
>    - GENERATED BY DEFAULT store a one (1) in that field and null
> references for the defaultText and defaultValue. So a 1 means that the
> default is a generated by default column.
> 
> 3) Add methods and fields as needed to DefaultInfo and DefaultInfoImpl
> 
> e.g. in DefaultInfo
> 
>       static final int DEFAULT_CLAUSE = 0; // regular DEFAULTur 
>       static final int GENERATED_DEFAULT = 1;
> 
>       /**
>           Return default type of column, one of DEFAULT_CLAUSE or
> GENERATED_DEFAULT
>       */
>       int getDefaultType()
> 
> 4) Only upgrade code (apart from testing) needed is the soft upgrade
> check to disallow GENERATED BY DEFAULT when running in soft upgrade mode.
> 
> 

I think this approach is very reasonable.

//I didn't know that we can use the spare field in the stored format ..
//I thought it was kind of terminator...

Aside from cleaning up, I would go on this way in DERBY-167.

Thanks a lot !

Best regards.

/*

         Tomohito Nakayama
         tomonaka@basil.ocn.ne.jp
         tomohito@rose.zero.ad.jp

         Naka
         http://www5.ocn.ne.jp/~tomohito/TopPage.html

*/
----- Original Message ----- 
From: "Daniel John Debrunner" <dj...@debrunners.com>
To: "Derby Development" <de...@db.apache.org>
Sent: Saturday, April 30, 2005 1:34 AM
Subject: Re: Question about softupgrade mode ..


> TomohitoNakayama wrote:
> 
>> Hello.
>> 
> 
>>> I think adding extra information to the DefaultInfo is the correct way
>>> and is the way the system was designed. The column's definition is
>>> through the interface DefaultInfo, thus allowing different object
>>> implementations to be stored in the column, representing additional
>>> information as needed.
>> 
>> 
>> Thinking freely in these days,
>> I came to thought it would be worth to rollback to first phase of
>> desicion aboout solution1-3.
> 
> I think you are close to a good solution for implementing GENERATED BY
> DEFAULT.
> 
> You other e-mails say that currently for GENERATED ALWAYS that no
> information is stored in the COLUMNDEFAULT column of SYSCOLUMNS, I
> assume that means a NULL.
> 
> Then you propose that you always store information in the COLUMNDEFAULT
> column for GENERATED ALWAYS and GENERATED BY DEFAULT, but this has some
> issues related to upgrade.
> 
> I think your proposal should be modified a little and take advantage of
> the current implementation of DefaultInfoImpl.
> 
> 1) Continue to store NULL in the COLUMNDEFAULT column of SYSCOLUMNS for
> GENERATED ALWAYS, means there is no default option. This makes sense,
> this column is not applicable for GENERATED ALWAYS
> 
> 2) For GENERATED BY DEFAULT store a non-NULL value in the COLUMNDEFAULT
> column of SYSCOLUMNS, using the an instance of the DefaultInfoImpl
> class. This class has a spare field in its stored format that is
> currently always zero, this is very useful to add meaning or
> functionality to its stored form. So I would propose
> 
>    - existing defaults continue as they are, the extra field becomes
>     a status field and a value of zero means a regular default.
> 
>    - GENERATED BY DEFAULT store a one (1) in that field and null
> references for the defaultText and defaultValue. So a 1 means that the
> default is a generated by default column.
> 
> 3) Add methods and fields as needed to DefaultInfo and DefaultInfoImpl
> 
> e.g. in DefaultInfo
> 
>       static final int DEFAULT_CLAUSE = 0; // regular DEFAULT
>       static final int GENERATED_DEFAULT = 1;
> 
>       /**
>           Return default type of column, one of DEFAULT_CLAUSE or
> GENERATED_DEFAULT
>       */
>       int getDefaultType()
> 
> 4) Only upgrade code (apart from testing) needed is the soft upgrade
> check to disallow GENERATED BY DEFAULT when running in soft upgrade mode.
> 
> 
> Dan.
> 
> 
> 
> 
> 
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>


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