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Subject: GemStone FAQ (v.1.0)

This article was archived around: 21 May 2006 04:23:19 GMT

All FAQs in Directory: databases
All FAQs posted in: comp.lang.smalltalk
Source: Usenet Version


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