• VOT:1 Checking out objects with a NOLOCK
• VOT:2 vcopydb to duplicate a database
• VOT:3 Improving performance for selects
• VOT:4 Lock modes supported by Versant ODBMS
• VOT:5 Installing different versions of Versant on same machine
• VOT:6 Distributing logs and system volumes of different disks
• VOT:7 Backing up and restoring databases on different machines
• VOT:8 Createdb fails by starting numerous obe's
• VOT:9 Error SM_E_DEVREADERROR ( VERSANT error 2751 )
• VOT:10 Error SM_E_NOFREEBUFFERS (VERSANT error 2713 )
• VOT:11 Error LOCK_WAIT_TIMEOUT (VERSANT error 2903 )
• VOT:12 How does Versant handle schema evolution ?
• VOT:13 Guidelines for using raw devices
• VOT:14 Invocation of obe's in Windows/NT
• VOT:15 Starting and stopping the VERSANTD process on Windows/NT
• VOT:16 Restrictions in Release 4.0.x for VERSANT on Windows/NT
• VOT:17 Possible cause for VERSANTD not starting on Windows/NT
• VOT:18 Duplicating databases
• VOT:19 Collections classes in Versant

Q.  VOT:1 Checking out objects with NOLOCK

A.  If objects are checked out from a group database into a personal database with NOLOCK, the checked-out 
    is created in the personal database with a new LOID.  

Q.  VOT:2 vcopydb to duplicate a database

A.  vcopydb requires the dba of the source db to be the same as the target db.
    To allow a user who does not own the database to copy it would cause the 
    security scheme provided by VERSANT to break.


Q.  VOT:3 Improving performance for selects


A.  vstats provides hit ratio for the BackEnd cache.  If the hit ratio for the BackEnd cache 
    is not very high, increasing the max_page_buffs in the backend profile should increase
    the performance.  

Q. VOT:4 Lock modes supported by  Versant ODBMS 

A) Versant supports four short lock modes: read lock (RLOCK), update lock
   (ULOCK), write lock (WLOCK), and no lock (NLOCK).  Versant provides
   object level locking and the locks can be aquired implicitly and explicitly
   When the user begins a session on a Versant database, a default lock read
   lock is set.  This implicit lock is placed on any object obtained by 
   dereferencing a "link", or casts a "link" to a pointer.  Deleting an object
   places an implicit WLOCK on the object.  The user has the ability to 
   modify the default lock mode as well as to acquire a lock mode on an 
   object explictly.

   dom->set_default_lock(lockmode)		//sets  the default lock mode
   aObject->acquireslock(lockmode)		//explicitly sets the lock mode

Q.  VOT:5 Installing different versions of Versant on same machine 

A:   Versant does not recommend installing different versions of Versant on the same machine. 
     If the user is compelled to install different versions of Versant on the same machine,  the steps
     are outlined below 
     
     Assume:
     
     You wish to install 3.0.14 and 4.0.7 on Solaris 2.4 machine
     The database and applications will run on the same machine.
     Versant 3.0.14 is installed at /usr/local/versant3/3.0.14 
     Versant 4.0.7 is installed at /usr/local/versant4/4.0.7
 
     Step 1: Install 4.0.7 by following the installation documentation   The oscssd 
     entry in /etc/inetd.conf should point to  4.0.7/sun4/bin/ss.d.

     Step 2:  Change the environment variables that will be 
     used by the applications that run on this machine. Assume the 
     combinations of applications and databases.

	1.  Application: 3.0.14 Database: 3.0.14

  	    VERSANT_ROOT@localhost = /usr/local/versant3
	    VERSANT_REL@localhost = 3.0.14
	
            Always qualify the database names as dbname@localhost.

        2.  Application: 3.0.14 Database: 4.0.7
		
	    No special environment variables are necessary. Please note: 
            The 3.0.14 applications have to be linked with the two-process 
	    Versant library (liboscfe).

	3.  Application: 4.0.7 Database: 4.0.7

	    No special environment variables are necessary.

Q. VOT:6 Distributing logs and system volumes of different disks
 
A. Distributing the logical.log, physical.log, and system to different directories can be achieved
   by modifying the paths of the files in profile.be.  Make sure the directories specified have 
   access permissions.  If startdb gets an error "Unable to open volume", it means that the permissions
   were denied to one of the directories specified in profile.be.	  

 

Q. VOT:7 Backing up and restoring databases on different machines

A. Create a databese with the same name and database id number.  Do a restore to 
   restore the database.  If there are additional volumes for the database, the 
   absolute path is required.  The best approach is to create symbolic links to simulate
   the path.   


Q. VOT:8 Createdb fails by starting numerous obe's
   

A. The name set for VERSANT_DBID_NODE does not match the 
   actual name of the server where the database is being created.
  
   Type in hostname at the command prompt to see the
   name of the machine and change the VERSANT_DBID_NODE
   setting on the server to this name.

   Note:
      1. On OS/2, check the TCP/IP configuration notebook for the
         name of the machine as  the hostname utility returns the 
         name in lower case even though the name configured may be 
         in mixed case.

       
Q. VOT:9 Error SM_E_DEVREADERROR ( VERSANT error 2751 )

A: This error is thrown as a result of a UNIX read system call failing.

   VERSANT expects a certain no. of bytes to be read in and
   does not get back the expected number.

   Possible cause: Corrupted disk sector.

Q. VOT:10 Error  SM_E_NOFREEBUFFERS (VERSANT error 2713 )


A: This error could be due to several reasons:

   1. an object requires more pages in the SDA buffer cache than
   is available.

   2. an object requires more contiguous space from the SDA memory
   manager than is available and there isn't enough swap space to
   add the requested new shared memory segments.  

   Solution for both scenario would be to increase max_page_buffs
   in profile.be.

   The choice of the appropriate value for max_page_buffs depends on the 
   application.  With 128M RAM, I would at least use up 32M for the buffer 
   cache (max_page_buffs = 2048).

   Turning commit_flush on or increasing the commit frequency
   will not help in this situation.

   See also page 8-7 of "Concepts and Usage Manual" and page 2-18 of
   "System Manual" for release 4.

Q. VOT:11 Error LOCK_WAIT_TIMEOUT (VERSANT error 2903 )

A: If an application is browsing the database with a RLOCK and another application has its
   default lock mode to ULOCK.  If the application with the ULOCK deferences objects, Versant
   will place a ULOCK on the objects it deferences implicitly.  In this case, the application holding
   objects with RLOCK will block the user with ULOCK and application will throw a Error 2903.
   The Versant Browser places RLOCK's on objects as its default. 

  Another example of implicit locking is marking an object as dirty
  automatically obtains a write lock on the object.

  If you change the default lock to RLOCK, then the application should not 
  encounter lock wait timeout error while dereferencing objects that the
  browser is accessing.

  To determine the current default lock, use get_default_lock(); to change
  the default lock, use set_default_lock().

Q. VOT:12 How does Versant handle schema evolution ?

   As applications evolve and new versions of software need to be installed
   in deployed applications, database schemas have a need to be evolved. 
   Versant provides "on-line" schema evolution.  At no time the database needs
   to be stopped for schema evolution to take place.  Versant provides "lazy"
   schema evolution which allows for the database to be running in a 24x7 
   environment.  When the schema is evolved, the class object is evolved
   and not the instances.  As the instances of the evolved class are accessed,
   the instances are evolved.  

Q. VOT:13 Guidelines for using raw devices


A. The size of the system volume must be large enough to store all objects
   and classes expected to reside in  the database at any time.

   A guideline for setting the size of sysvol is
   guideline =  min_size + (1.25 * (avg_o_size + 40) * num_objects )

   The min_size = 1800K
   avg_o_size = avg size in bytes of objects in the database.
   num_objects = no of objects.
   You may specify raw device for the system vol.

   The size of the log depends upon the no of transactions.  The guideline to 
   follow is

   plogvol
     guideline = 2 * (max_o_size + 1K) + 32K

     subsitute the size of the largest object in the database for max_o_size.

   llogvol 
      guideline = 32k + (2 * (max_o + 100)) * num_o_per_tr * num_tr

      substitute max_o = size in bytes of the largest object in the database.
                   num_o_per_tr = largest no of objects involved in the transaction.
                   num_tr = max no of concurrent transactions.

Q. VOT:14 Invocation of obe's in Windows/NT

A. VERSANT uses the Windows NT service mechanism to spawn obe's.
   The installation script on Windows/NT installs a NT service called VERSANTD
   and the executable that acts as the service provider is called 
   winverd.exe. The first time the service is started, it starts
   a process by running an executable called versantd.exe

   The versantd process  listens for traffic on the VERSANT related port 
   (identified by name oscssd)

   When there is traffic on this port,  inetd invokes the VERSANT daemon 
   ss.exe which in turn invokes the actual VERSANT server process called obe.

  (5019 can be changed to a different number).


Q. VOT:15 Starting and stopping the VERSANTD process on Windows/NT

   1. Go over to the control panel and select the services icon. If installed,
      VERSANTD should listed in the list of services. The type of
      startup should be Automatic. Press start to start the service if
      not started already.
   2. Use "net start versantd" to start the service from the NT command 
      prompt.

      If the service is not installed already, one can install it by typing in
    

           instsrv versantd \winverd.exe
  
      where  = c:\versant\4_0_7\nt\bin if
      VERSANT is installed in c:\versant and the VERSANT release is 4.0.7.


      The service can be started in either of the 2 ways shown above.
      To stop the VERSANTD process from the control panel,  select the services icon
      and use the stop button after selecting the versantd service from the
      list of services displayed.

      Another way to stop the service is by using 
          "net stop versantd"    from the NT command prompt.

Q.  VOT:16 Restrictions in Release 4.0.x for VERSANT on Windows/NT

A.  Long file names with spaces are not supported for the VERSANT
    release directory and database directories.
    
    Long user names with spaces are not supported.
    
    SYSTEM cannot be a valid user of a VERSANT database.

Q.  VOT:17 Possible cause for VERSANTD not starting on Windows/NT

A   The executable winverd.exe needs to know the location of
    the versantd.exe executable on the system as it needs to execute 
    this program as part of service startup.
 
    The location is established by a config. file with name vrxxyyzz.ini
    where xx=04, yy=00, zz=05 for Release 4.0.5
    and xx = 03, yy=00,zz=14 for Release 3.0.14.

    This file should be located in the Windows NT home directory
    ( usually c:\winnt35). 

    The file contains one line:

    VERSANT_ROOT  
    where VALUE_OF_VERSANT_ROOT = c:\versant if VERSANT is installed
    in c:\versant.

     
    If this file is not found, VERSANTD  will not start as VERSANT_ROOT is
    not known 

Q. VOT:18 Duplicating databases
A  There are many different ways of duplicating databases.  The first
   procedure is to make an identical copy of the database, that is the
   LOIDs in the two databases are the same.  There are two ways to
   accomplish this.  The first is to use vcopydb utility.  This copies 
   the contents of db1 into db2.  vcopydb assumes db2 has not been 
   created and makes a duplicate of the database.  The second mechanism
   is to write a program that selects all the object in the database and
   then does a 
   dom->migrateobj(selected_objects,primary_db,copy_to_db,O_MVSYNC).

   One of the advantages of using the migrateobj is that is allows the user
   to copy only certain classes, or even only certain instances.  
     

   The next copy database is for users that do not care about the LOIDs and
   want to copy the database logically.  Versant provides a utility vexport
   that creates an ASCII dump of the database.  Versant provides a utility,
   vimport that takes the ASCII file and create logical copies in a database.
   Please see 3-40 and 3-45 for usage of vexport and vimport.


Q.  VOT:19 Collections  in Versant 
A   All of Versants collections are logical collections.  When an object is 
    removed from the collection, the object is removed from the collection, 
    but not from the database.  It is the responsibility of the application 
    programmer to delete the physical object from the collection if they 
    want the behavior of a physical collection
     
 

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