db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mamta Satoor" <msat...@gmail.com>
Subject Re: how should store get an object based on format id and collation id?
Date Sat, 14 Apr 2007 07:03:43 GMT
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
10.3but 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.
>
>
>
>

Mime
View raw message