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GemStone FAQ (v.1.0)


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Archive-name: databases/GemStone-FAQ
Posting-Frequency: monthly
Last-modified: Oct 26,1997
Version: 1.0
URL: http://www.ipass.net/~vmalik/gemstone.html

See reader questions & answers on this topic! - Help others by sharing your knowledge
____________________________________________________________________________

GemStone Frequently Asked Questions
Copyright =A9 1994 Vikas Malik
All Rights Reserved

This FAQ may be posted to any USENET newsgroup, on-line service, or BBS
as long as it is posted in its entirety and includes this copyright=
 statement.

This FAQ may not be distributed for financial gain.

This FAQ may not be included in commercial collections or compilations
without express permission from the author.
____________________________________________________________________________

Vikas Malik - vmalik@ipass.net
Knowledge Systems Corporation
____________________________________________________________________________

Contents

Q. What is GemStone?=20
Q. How do I spell GemStone?
Q. What is the Stone?
Q. What is a Gem?
Q. What is a Repository?
Q. What is the difference between a linked and RPC application?
Q. What is GemBuilder?
Q. What is GBSM?
Q. How do I log into GemStone programmatically?
Q. What are the two different types of transaction modes in GemStone?
Q. What is a connector?
Q. What are the different kinds of connectors?
Q. What is the difference between a global connector and a session=
 connector?
Q. Do I need to define a connector for every object in my application?
Q. What is a root object?
Q  What is a symbol list?
Q. What are the names of default symbol dictionaries of a GemStone user?
Q. How do I invoke a debugger in GemStone?
Q. What is the difference between the terms faulting and flushing?
Q. How do I remotely excute code in GemStone from Smalltalk side?
Q. What is a forwarder?
Q. How do I create a forwarder?
Q. What is the difference in results of sending the following messages to a=
=20
forwarder?
	aGSForwarder   name    and   aGSForwarder   fwname
Q. What is a replicate?
Q. What is a stub?
Q. How do I control the number of levels to replicate when updating an=
 object=20
from GemStone to Smalltalk?
Q. How do I unstub a stub?
Q. Can I pass a stub as an argument to a primitive method?
Q. How do I ensure that an object is never replicated to contain a stub down=
 to=20
a certain level?
Q. How do I convert a replicate into a stub?
Q. What is the result of sending a message to a stub?
Q. What is the difference between lazy and immediate fault policy?
Q. What do I mean by class history of a GemStone class?
Q. How do I remove a version of GemStone class?
Q. How do I find the latest version of a GemStone class?
Q. How do I migrate all the instances of a class to its latest version?
Q. How do I remove all the old versions of a class?
Q. What is the difference between the results of sending #asLocalObject and=
=20
#asLocalObjectCopy messages to  aGSObject?
Q. How do I mark a Smalltalk object as dirty?
Q. How do I mark objects dirty automatically without sending #markDirty in=
=20
setter methods?


Q. What is GemStone?
Ans. GemStone is an Object- Oriented database.

Q. How do I spell GemStone?
Ans. GemStone is always spelled with upper case S. Some smart recruiters=
 will=20
look for upper case S in your resume.

Q. What is the Stone?
Ans. The stone process handles locking and concurrent access to objects in=
 the=20
repository. Each repository is monitored by a single stone.

Q. What is a Gem?
Ans. Gem is the object server for user application. The Gem reads the
repository=20
as the application accesses objects, and it updates the repository when an
application=20
commits a transaction. A repository can have more than one Gem process.

Q. What is a Repository?
Ans. Repository stores GemStone classes and persistent objects.

Q. What is the difference between a linked and RPC application?
Ans. In a linked application, Gem is integarted with the application into a
single=20
process whereas in a RPC application, Gem runs as a separate process and
responds=20
to RPCs from the application.

Q. What is GemBuilder?
Ans. GemBuilder is a set of classes and primitives installed in client
smalltalk=20
image to facilitate working with the two object spaces (Smalltalk-Client &=
=20
GemStone-Server).=20

Q. What is GBSM?
Ans. GBSM is global that refers to the sole instance of GbsSessionManager
class.=20
GBSM manages all known GemStone sessions and keeps track of the current=
 session.

Q. How do I log into GemStone programmatically?
Ans. 	GBSM   loginWithParameters: aGbsSessionParameters.
	or
	aGbsSessionParameters login.

Q. What are the two different types of transaction modes in GemStone?
Ans. 1. Automatic transaction mode: A new transaction begins automatically=
 when=20
one commits or aborts a transaction.
2. Manual transaction mode: Transactions begin as a result of explicit=
 request.

Q. What is a connector?
Ans. A connector connects a GemStone object and a client smalltalk object
when a=20
session logs in to the database.

Q. What are the different kinds of connectors?
Ans. 1. Name connector connects a smalltalk object with a GemStone object=
 based=20
on their names (which can be different).
2. Fast connector keeps a direct reference to a smalltalk object and a=
 GemStone=20
object id. This makes the connection fast because no resolution is=
 necessary.

Q. What is the difference between a global connector and a session=
 connector?
Ans. A global connector connects two objects whenever any session is logged=
 in=20
whereas a session connector connects two objects only when a specific=
 session=20
is logged in.

Q. Do I need to define a connector for every object in my application?
Ans No, because a connector connects not only the immediate object but also=
 all=20
those objects that can be reached from it. Define connectors for only the=
 root=20
objects of the persistent subsystems.

Q.What is a root object?
Ans. Root objects of an application are the persistent objects from which=
 all=20
other persistent objects can be reached. The most common kinds of root
objects are
(i) Global variables
(ii) Class variables
(iii) Class instance variables

Q What is a symbol list?
Ans. A symbol list is an array of symbol dictionaries. Symbol list is used=
 in=20
compilation of GemStone code, in order to resolve references to objects by
name.=20
Each GemStone user has a symbol list. Only objects named in symbol=
 dictionaries=20
in a user=92s symbol list are visible to that user.

Q. What are the names of default symbol dictionaries of a GemStone user?
Ans. Globals, UserGlobals, Published and UserClasses.

Q. How do I invoke a debugger in GemStone?
Ans. Insert    self pause.    in a GemStone method.

Q. What is the difference between the terms faulting and flushing?
Ans. The term faulting refers to moving modified GemStone objects into the
client=20
Smalltalk , either creating a client Smalltalk replicate or updating an
existing=20
replicate. The term flushing refers to moving modified client Smalltalk=
 objects=20
into GemStone.

Q. How do I remotely excute code in GemStone from Smalltalk side?
Ans. 	aGSSession   excute: aString
	aString contains GemStone smalltalk code.

	aGSObject   remotePerform: aSelector.

Q. What is a forwarder?
Ans. A forwarder is a client smalltalk object whose state and behavior are
actually=20
in GemStone. The forwarder knows which GemStone object it represents, and
responds=20
to all messages by passing them to appropriate GemStone object. Forwarders=
 are=20
implemented by class GSForwarder. Its gsObj instance variable points to the
proxy=20
representing the GemStone object.

GSForwarder implements #doesNotUnderstand: as following.
#doesNotUnderstand: aMessage

	^gsObj=20
		remotePerform: aMessage selector
		withArgs: aMessage arguments

Q. How do I create a forwarder?
Ans. 1. aGSConnector   postConnectAction: #forwader
2.  aGSSession   fwat: anObject
3.  by implementing  class method #instancesAreForwarders to specify all
instances=20
of a class are forwarders.
4.  by sending #asForwarder message to an instance of GSObject class.

Q. What is the difference in results of sending the following messages to a
forwarder?
	aGSForwarder   name    and   aGSForwarder   fwname.
Ans.   aGSForwarder    name   returns a replicate.
       aGSForwarder    fwname   returns a forwarder.

Q. What is a replicate?
Ans. A replicate is a Smalltalk copy of a GemStone object. Messages sent to=
=20
replicates require no communication with GemStone for processing.

Q. What is a stub?
Ans. A stub is an empty placeholder that knows nothing except which object=
 it=20
represents in GemStone. It is implemented by GSObjectStub class.=20

Q. How do I control the number of levels to replicate when updating an=
 object=20
from GemStone to Smalltalk?
Ans. By implementing #defaultGStoSTLevel method of GSSession class. A level=
 of=20
0 means no limit, replicate the entire object. A level of 2 means retrieve=
 root=20
object and each object it references . Objects at level 3 are converted into
stubs.

Q. How do I unstub a stub?
Ans. By sending #fault message to a stub.

Q. Can I pass a stub as an argument to a primitive method?
Ans. No.

Q. How do I ensure that an object is never replicated to contain a stub down=
 to=20
a certain level?
Ans. Implement class method #noStubLevel. Its return value should be an=
 integer=20
specifying the number of levels to replicate.

Q. How do I convert a replicate into a stub?
Ans. By sending #stubYourself message to replicate.

Q. What is the result of sending a message to a stub?
Ans. It replicates the GemStone object it represents as a Smalltalk object,
then=20
become that object and forwards the message. GSObjectStub implements
#doesNotUnderstand:=20
as following.

#doesNotUnderstand: aMessage
	^self fault=20
		perform: aMessage selector
		withArguments: aMessage arguments.

Q. What is the difference between lazy and immediate fault policy?
Ans. In lazy faultPolicy a change initiated in GemStone causes Smalltalk
replicate=20
to be turned into a stub whereas in immediate faultPolicy a chage initiated
in GemStone=20
replicates  the client Smalltalk immediately.

Q. What do I mean by class history of a GemStone class?
Ans.  GemStone supports multiple versions of a class. It keeps track of=
 these=20
versions in a class history object. Sending #classHistory message to a class=
=20
returns its class history.

Q. How do I remove a version of GemStone class?
Ans=20
	aClassHistory  removeVersion: aClass

Q. How do I find the latest version of a GemStone class?
Ans  aClass classHistory last.

Q. How do I migrate all the instances of a class to its latest version?
Ans.  aClass migrateInstancesTo: aClass classHistory last.

Q. How do I remove all the old versions of a class?
Ans.=20
	1 to: ( aClass classHistory size - 1)
			do: [ :each |=20
				aClass classHistory removeVersion: ( aClass classHistory at: each)].

Q. What is the difference between the results of sending #asLocalObject and=
=20
#asLocalObjectCopy messages to  aGSObject?
Ans. #asLocalObject returns a replicate. #asLocalObjectCopy returns a local
deep=20
copy of the GemStone object repesented by the receiver. This resultant=
 object=20
doesn=92t maintain the transparency between Smalltalk and GemStone.

Q. How do I mark a Smalltalk object as dirty?
Ans    anObject markDirty. It is generally included in the setter methods=
 for=20
the object.=20

Q. How do I mark objects dirty automatically without sending #markDirty in=
=20
setter methods?
Ans 	aClass  markDirtyOnInstVarAssign  marks the objects of aClass dirty on=
=20
assignment of instance variables.
	aClass  markDirtyOnAtPut  marks the objects of aClass dirty if they receive=
=20
#at:put: messages.
*********************************************************************

         _________
         \        \
          \        \               ___    __
           \        \              \  \  / |
           /\        \              \  \/  |
         O/  \ *****  \____________  \ /   |
     \ /   ############## ***+++^^^^^^^\   \
      X **################***+++^^^^^^^ \   \
     / \   ############## ***+++^^^^^    \___\
               / \       \          \o
             O/   \       \
                   \       \
                    \       \
                     \       \
                      \_______\    =20
                                  =20


 		I'D  RATHER  BE  FLYING  !!!

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