Data Dictionary Cache question

[Yip Ng <yi...@gmail.com>]

Hi

   I am looking through the data dictionary code and I am wondering why the
system needs to clear *ALL* the data dictionary caches (table descriptors,
etc.) at startWriting(), what is the reason behind this?  Wouldn't clearing
just the "affected" descriptor(s) in the DDL's constant action enough?

Yip

Re: Data Dictionary Cache question

[Mamta Satoor <ms...@gmail.com>]

Yip,

My guess is that startWriting clears all the data dictionary caches so
that individual sql statement implementations don't have to worry about
dealing with keeping the cache clean. Because if a statement missed cleaning
the cache (like it happened for ALTER TABLE ADD COLUMN) then we could end up
with bugs like DERBY-1847. So, I guess for code maintainability, Derby might
have chosen to cleanup all the caches. I don't know why this logic is not
applied to permission cache though. startWriting() does not cleanup the
permission cache and looks like it is expected to be done by the inidividual
sql statements whereever necessary.

But like I said, this is just a theory I deducted from the current
implementation. Someone else might have more concrete answer.
Mamta

On 9/25/06, Yip Ng <yi...@gmail.com> wrote:
>
> Hi
>
>    I am looking through the data dictionary code and I am wondering why
> the system needs to clear *ALL* the data dictionary caches (table
> descriptors, etc.) at startWriting(), what is the reason behind this?
> Wouldn't clearing just the "affected" descriptor(s) in the DDL's constant
> action enough?
>
> Yip
>
>