I spent some time on points 1(using Monitor to get dvd directly) and 3(optimized allocation, caching some of the work.) which requires us to solve the problem of how to get the InstanceGetter to return the correct DVD for character types. Let me first briefly describe how the InstanceGetter works for DVDs currently.
 
 
***********description on InstanceGetter for DVD********
I think the code dealing with getting an InstanceGetter for a DVD from a formatid is currently isolated in BaseMonitor.classFromIdentifier(int fmtId). BaseMonitor has a class level field called rc2 which is an array of same length as  StoredFormatIds.TwoByte. The elements in rc2 will be InstanceGetters. Every time BaseMonitor.classFromIdentifier(int fmtId) is called, the method first checks if there is already an InstanceGetter in the rc2 array for the passed format id. If yes, then it simply returns that cached InstanceGetter from rc2. But if this is the first time this method is being called for the passed format id, then we first get the name of the InstanceGetter from RegisteredFormatIds using the format id passed to the method. (For DVDs, the name of that InstanceGetter would be org.apache.derby.iapi.types.DTSClassInfo). Using that name from RegisteredFormatIds, we create a Class object(for DVDs, that Class object would be DTSClassInfo) and check if that Class is of type FormatableInstanceGetter. If yes, then we create an instance of that Class object(for DVDs, this will return an object of type DTSClassInfo) and set the format id on it. And as a last step, we cache this FormatableInstanceGetter in the rc2 array for future. So, in future, if BaseMonitor.classFromIdentifier(int fmtId) gets called for the same fmtId, we can simply return the cached InstanceGetter from rc2.
************************************************************
 
This current code will work fine for non-character type DVDs in Derby 10.3 but it won't work for character type DVDs. For example for the format id corresponding to SQL type CHAR, we want to return DVD of type either SQLChar or CollatorSQLChar, depending on the value of collation type. But existing code will always return SQLChar. What we want is for one format id to represent 2 DVDs and the deciding factor is the collation type. In order to support this, I am proposing following changes to the logic above so that we can have InstanceGetter return the correct DVD, even for character types.
 
**********************************changes proposed to InstanceGetter******************
For collation sensitive format ids (those corresponding to character types), I am proposing to create a new InstanceGetter class called CollationSensitiveDTSClassInfo which will extend DTSClassInfo . We will change RegisteredFormatIds.TwoByte for such format ids to use org.apache.derby.iapi.types.CollationSensitiveDTSClassInfo. We will also need to remove the code for collation sensitive format ids from DTSClassInfo since they will be handled in the new InstanceGetter, which is CollationSensitiveDTSClassInfo.This new InstanceGetter class will have two additional fields called collatorForDVD and collationType. And it will have 2 setter methods, namely, setRuleBasedCollator and setCollationType. The public Object getNewInstance() method on this InstanceGetter will have code like following (Note that, I will need to add a new constructor on CollatorSQL.. classes to take just the RuleBasedCollator.)

               switch (fmtId) {
                /* Wrappers */
                case StoredFormatIds.SQL_CHAR_ID:
                      if (collationType == StringDataValue.UCS_BASIC)
                           return new SQLChar();
                      else
                           return new CollatorSQLChar(collatorForDVD);
                case StoredFormatIds.SQL_VARCHAR_ID:
                      if (collationType == StringDataValue.UCS_BASIC )
                           return new SQLVarchar();
                      else
                           return new CollatorSQLVarchar(collatorForDVD);
                case StoredFormatIds.SQL_LONGVARCHAR_ID:
                      if (collationType == StringDataValue.UCS_BASIC)
                           return new SQLLongvarchar();
                      else
                           return new CollatorSQLLongvarchar(collatorForDVD);
                case StoredFormatIds.SQL_CLOB_ID:
                      if (collationType == StringDataValue.UCS_BASIC)
                           return new SQLClob();
                      else
                           return new CollatorSQLClob(collatorForDVD);
                default: return null;
               }
The collatorForDVD will need to be set on this new InstanceGetter only the first time around when it is created. If user has requested territory based collation, then collatorForDVD will be set to the Collator that is derived from the database's territory. If user wants UCS_BASIC collation, then collatorForDVD will be set to JVM's default Collator. The collationType is subject to change depending on if store is looking for character types belonging to system tables (such types will always have collation type of UCS_BASIC) or for character types belonging to non-system tables (such types will have the collation type of UCS_BASIC/TERRITORY_BASED depending on what user has requested for the database). Based on this, the logic for DVF.instanceGetterFromIdentifiers(fmtId, collationType) will look as follows

DVF will have a class level field called instanceGettersForFormatIds which will be an array of same length as  StoredFormatIds.TwoByte. The elements in instanceGettersForFormatIds will be InstanceGetters. Every time DVF.instanceGetterFromIdentifiers (int fmtId, int collationType) will be called, the method will first check if there is already an InstanceGetter in the instanceGettersForFormatIds array for the passed format id. If yes, then it will check if the instanceGetter is of type CollationSensitiveDTSClassInfo and if yes, then it will set the collationType on that InstanceGetter to the collationType passed to instanceGetterFromIdentifiers method and it will return that InstanceGetter. If the InstanceGetter is not CollationSensitiveDTSClassInfo, then it will simply return the InstanceGetter obtained from the instanceGettersForFormatIds array.

In the case, DVF.instanceGetterFromIdentifiers(int fmtId, int collationType) does not find InstanceGetter cached for the passed format id in instanceGettersForFormatIds array, then it will first get the name of the InstanceGetter from RegisteredFormatIds using the format id passed to the method. (For non-character DVDs, the name of that InstanceGetter would be org.apache.derby.iapi.types.DTSClassInfo. For character DVDs, the name of that InstanceGetter would be org.apache.derby.iapi.types.CollationSensitiveDTSClassInfo). Using that name from RegisteredFormatIds, we will create a Class object(for DVDs, that Class object would be DTSClassInfo/CollationSensitiveDTSClassInfo) and will check if that Class is of type  FormatableInstanceGetter. If yes, then we create an instance of that Class object(for non-character DVDs, this will return an object of type DTSClassInfo. For character DVDs, this will return an object of type CollationSensitiveDTSClassInfo) and set the format id on it. For non-character DVDs, as a last step, we will cache this FormatableInstanceGetter in the instanceGettersForFormatIds array for future. But for character DVDs, we will set the collationType and RuleBasedCollator on the InstanceGetter AND then save it in instanceGettersForFormatIds.

As usual, I might have provided lot of information but hopefully it will help understand the logic clearly. I will start looking at implementing this but if anyone has any feedback on the logic, I will appreciate that.

thanks,
Mamta

On 4/12/07, Mike Matrigali <mikem_app@sbcglobal.net > wrote:


Mamta Satoor wrote:
> Mike, the following code will be part of DataValueFactory and hence it
> will be part of the interface. Please let me know if I am not very clear
> with what I am proposing or if you forsee problems with this logic.
> if (dvd instanceof StringDataValue)
>               dvd = dvd.getValue(dvf.getCharacterCollator(type));

My comment isn't really the logic, I think we are just not talking about
the same area.  I think the code above belongs hidden behind the new
interfaces in the implementation logic of the data factory and data
types, not an example of what callers of the datatype should be doing.
>
> Also, in the following line below
> "I'll look at building/using DataFactory interface.  It will be some"
> you mean DataValueFactory interface, right?
>
> Mamta

Yes I meant DataValueFactory interface.  Let's work together on getting
the DataValueFactory interface right.

So far I have uncovered to basic ways store creates "empty" objects.
Note that store really only needs "empty" objects, ie. it is going
to initialize the state of these objects from disk by calling each
objects readExternal() method.  But we have decided to not store
the collation info as state in the object so somehow we need to get
that info into the empty objects.

The ways store currently creates these objects:

1) using Monitor to get dvd directly:
   dvd = Monitor.newInstanceFromIdentifier (format id)

   o I think this use is best implemented as Mamta suggests, just
     providing a non-static interface on the DataValueFactory.
     something like:

     DataValueFactory dvf = somehow cache and pass this around store;
     dvd = dvf.newInstance(format id, collation id);

     at this point dvd can be used to correctly compare against other
     dvd's in possible collate specific ways.

2) using existing dvd's class to get a new "empty" dvd that matches it
   (which is why it does not call clone).
   dvd = dvd.getClass().newInstance()

   o less sure about this one.  Seems like we need a new dvd interface
     that does the equivalent thing.  I believe the original code got
     here because the original store code did not deal with DVD's it
     just got objects, so could not make dvd calls.  There is a
     getNewNull() interface, anyone know if there is any runtime work
     that would be saved over this by creating a
     getNewEmpty() interface?

    dvd = dvd.getNewEmpty();

    at this point dvd can be used to correctly compare against other
     dvd's in possible collate specific ways.

3) optimized allocation, caching some of the work.  This is used
   where one query may generate large number of rows - for instance
   hash table scan and sorter calls.  Here the idea is to do some
   part of the work once leaving an InstanceGetter which then can
   repeatedly give back new objects in the most optimized way:

   called once:
   InstanceGetter = Monitor.classFromIdentifier(format id)

   called many times:
   dvd = InstanceGetter.getNewInstance()

   o something like the following would be the direct conversion.  Note
     that implementation of the Instance getter is probably more complex
     now.  It can't just remember a single class and call new instance
     on it.  It has to cache some info on what class to create and what
     collation to set in it.

   called once
   DataValueFactory dvf = somehow cache and pass this around store;
   InstanceGetter =
         dvf.instanceGetterFromIdentifiers(format id, collation id)

   called many times:
   dvd = InstanceGetter.getNewInstance()

again at this point dvd can be used to correctly compare against other
     dvd's in possible collate specific ways.



All 3 of these uses have to be replaced to allow store to create
"correct" types which can be used in possible string comparisons.