Mamta Satoor wrote:
Hi Dan,
The problem we are trying to solve is provide a way to Store so that it
can call a method (say it's called
getInstanceGetterForFormatIDandCollationType) on DVF with format id &
collation type and get an InstanceGetter for that combination.
Why use InstanceGetter here?
Like Mike
mentioned in his earlier mail (in this same thread, dated April 12th,
2nd mail from Mike) with point 3), Store will call this method once and
call getInstance on that InstanceGetter multiple times to get the right
DVD. If we don't change the InstanceGetter as I suggested, then that
would mean that we will be creating 2 DVD objects for every character
DVD through Store code. The worst part is we will be doing this
unnecessary creation of 2 DVDs even for databases which want default
collation. The 2 DVD creation I am talking about are first, through
InstanceGetter, we will get say SQLChar. Then at the time of actual
collation comparison, it will have to call something like
StringDataValue.getCollationValue(int collationType) to get another DVD
to make sure that the collation is being performed with write DVD.
It doesn't have to return another DVD, it can return itself if it is of
the correct type, thus no additional overhead for UCS_BASIC collation.
Thus this switch would happen once for the first collation, not every
collation, and of course not happen at all if no collation is involved.
What I am suggesting does not make InstanceGetter complicated. It is
pretty simple implementation. All I am proposing is to have special
InstanceGetter class for collation sensitive DVDs. This new
InstanceGetter class will have RuleBasedCollator (which will be set the
first time this InstanceGetter is created for the given database through
the DVF) and it will have collation type(this collation type will always
be set to whatever collation type the
getInstanceGetterForFormatIDandCollationType was called with. This
collation type will determine which kind of DVD to generate ie one with
default collation or one with terriotry based collation). You mentioned
in your mail that "I got a little lost in the details". Please let me
know where it was unclear and I can try to explain it better.
Could you show an example of how the store will be calling the code you
are describing? Maybe that would help me out.
As for your question about "does it take account of the fact that the
registered format ids are system wide and there can be databases with
different default collations in the same system?" My understanding is
that there is one DVF per database and these InstanceGetters will be
saved on DVF and hence I do not forsee any problems in having multiple
databases with different collations in same Derby system.
Dan.
