DB-13: Understanding VSTs By Paul Guggenheim

Copyright © 2005 Paul Guggenheim & Associates 2 DB-13: Understanding VSTs 2 About PGA  Working in Progress since 1984 and training Progress programmers since 1986  Designed six comprehensive Progress courses covering all levels of expertise  Major consulting clients include Foxwoods Casino, Health Informatics, Bank One, Textron Fastening Systems, and American Academy of Orthopaedic Surgeons

Copyright © 2005 Paul Guggenheim & Associates 3 DB-13: Understanding VSTs 3 What are VSTs ?  VST stands for Virtual System Table.  VSTs provide 4GL access to information contained in the Progress Monitor (promon) utility.  VSTs are schema tables that are stored in memory.

Copyright © 2005 Paul Guggenheim & Associates 4 DB-13: Understanding VSTs 4 Why Use VSTs ?  VSTs may be easily integrated into existing Applications.  Some startup parameters may be updated through VSTs.  Statistical Database Performance Reporting can be easily accomplished.  The Databases can be constantly monitored from within the Application.  Additional information about locking conflicts may be provided to the end-user.

Copyright © 2005 Paul Guggenheim & Associates 5 DB-13: Understanding VSTs 5 Accessing VSTs  VSTs are metaschema tables  Automatically included in Version 9  Must enable them in Version 8 with the following command: proutil dbname –C enablevst  To look at in GUI Dictionary, select: View->Show Hidden Tables  To look at in CHUI Dictionary, enter VST table name

Copyright © 2005 Paul Guggenheim & Associates 6 DB-13: Understanding VSTs 6 Viewing VSTs  VSTs are records in the _file metaschema table  _file-number range for VSTs (9.1D): to  Two new tables were added to OpenEdge 10.  _Code-Feature  _Database-Feature  One new field is added to OpenEdge 10.  _server._server-pendconn

Copyright © 2005 Paul Guggenheim & Associates 7 DB-13: Understanding VSTs 7 VST Inquiry  In program vstinq.p, the VST schema may be viewed.

Copyright © 2005 Paul Guggenheim & Associates 8 DB-13: Understanding VSTs 8 VST Characteristics  Every VST has one field that ends in ‘id’.  This field serves as the VST’s unique index.  This field is sequentially numbered from 1.  Exception is _TxeLock where Id field is ?.

Copyright © 2005 Paul Guggenheim & Associates 9 DB-13: Understanding VSTs 9 VST Characteristics  Many VSTs pre-allocate records based upon startup parameters. For example: proserve school -n 3 -Mn 3 -L 250 -B 500 produces a –n of 4.  Progress adds an extra user for shutting down the database or promon.

Copyright © 2005 Paul Guggenheim & Associates 10 DB-13: Understanding VSTs 10 VST Characteristics  Let’s look at the _Trans table:

Copyright © 2005 Paul Guggenheim & Associates 11 DB-13: Understanding VSTs 11 VST Characteristics  The default initial values in most VST fields is unknown (?).  The –Mn value is 3.  One record for each server and the one record for the database broker is displayed.

Copyright © 2005 Paul Guggenheim & Associates 12 DB-13: Understanding VSTs 12 VST Characteristics  Let’s look at _UserLock table. It shows which locks a particular user currently holds.

Copyright © 2005 Paul Guggenheim & Associates 13 DB-13: Understanding VSTs 13 VST Characteristics  _UserLock-Id 1 is the broker, 2,3 and 4 are the servers, 5,6 and 7 are connected users and 8 is a promon session.  The formula for this table is: –n + -Mn + 2 –n + -Mn + 2 where –n is the startup number of users.  Since the –L is 250, Progress rounds it to the nearest multiple of 32 which is 256.

Copyright © 2005 Paul Guggenheim & Associates 14 DB-13: Understanding VSTs 14 VST Characteristics  The _Lock file will look like the following:

Copyright © 2005 Paul Guggenheim & Associates 15 DB-13: Understanding VSTs 15 Resolving Locking Conflicts  As a developer, you had 2 choices in resolving locking conflicts: Option 1: Let Progress handle it.

Copyright © 2005 Paul Guggenheim & Associates 16 DB-13: Understanding VSTs 16 Resolving Locking Conflicts  As a developer, you had two choices in resolving locking conflicts: Option 2: Handling locking conflicts in the procedure repeat: prompt-for student.student-id. prompt-for student.student-id. find student using student-id exclusive-lock no-wait no-error. find student using student-id exclusive-lock no-wait no-error. if available student then update sfirst-name slast-name. if available student then update sfirst-name slast-name. else if locked student then do: else if locked student then do: find student using student-id no-lock no-error. find student using student-id no-lock no-error. message "Student record is locked” skip message "Student record is locked” skip "Please wait until later." view-as alert-box. "Please wait until later." view-as alert-box. end. end. else else message "Student number does not exist" view-as alert-box. message "Student number does not exist" view-as alert-box.end.

Copyright © 2005 Paul Guggenheim & Associates 17 DB-13: Understanding VSTs 17 Resolving Locking Conflicts  Problem with Option 1:  User has to undo their transaction.  The stop key, unless trapped, forces the user to the beginning of the application.  Problem with Option 2:  User doesn’t know who has locked the record…UNTIL VSTs!

Copyright © 2005 Paul Guggenheim & Associates 18 DB-13: Understanding VSTs 18 Resolving Locking Conflicts  Adding the statements below now provides the user with additional information about who has the record locked: find first _lock where _lock-recid = integer(recid(student)) no-error. message "Student record is locked by user:" _lock-name skip "Please wait until later." view-as alert-box. "Please wait until later." view-as alert-box.

Copyright © 2005 Paul Guggenheim & Associates 19 DB-13: Understanding VSTs 19 Record Locking Inquiries  For each user, Progress provides up to 512 locked records for display and lookup.

Copyright © 2005 Paul Guggenheim & Associates 20 DB-13: Understanding VSTs 20 Record Locking Inquiries  In lockinq.p, we start with the _UserLock table to show available users in a browse.  For each user selected there is another browse that shows the locked records for that user, it’s table name, RECID and lock flags.  To accomplish this, a temp-table is built storing the RECID and chain number from the corresponding array fields in the _UserLock table.

Copyright © 2005 Paul Guggenheim & Associates 21 DB-13: Understanding VSTs 21 Record Locking Inquiries  In lockinq.p, we start with the _UserLock table to show available users in a browse.  The second query is opened using this RECID and chain number to read the _Lock record to get the table number.  The table number is then used to read the _file metaschema table to get the table name for the browse.

Copyright © 2005 Paul Guggenheim & Associates 22 DB-13: Understanding VSTs 22 Record Locking Inquiries  In lockinq.p, we start with the _UserLock table to show available users in a browse.  For each locked record selected, the table name and RECID are passed to the getfieldvalues procedure which dynamically creates a query for that record.  It then calls the procedure showtable which displays the field names and values for that locked record using the tfld temp-table.

Copyright © 2005 Paul Guggenheim & Associates 23 DB-13: Understanding VSTs 23 Record Locking Inquiries

Copyright © 2005 Paul Guggenheim & Associates 24 DB-13: Understanding VSTs 24 4GL User Disconnect  The next program, disuser.p, allows someone to disconnect a user from within the 4GL.  The program uses the _connect and _myconnection VSTs.

Copyright © 2005 Paul Guggenheim & Associates 25 DB-13: Understanding VSTs 25 4GL User Disconnect  The next program, disuser.p, allows someone to disconnect a user from within the 4GL.  The _connect table is used for the query and browse for connected users.  The _connect-usr values that are unknown and the previously disconnected users (connect-disconnect = 1) are filtered out.  The _myconnection table is used to prevent someone from disconnecting themselves.  This table was added to V9 to make it easy to identify which connection is the current session.

Copyright © 2005 Paul Guggenheim & Associates 26 DB-13: Understanding VSTs 26 4GL User Disconnect  The next program, disuser.p, allows someone to disconnect a user from within the 4GL.  The actual user disconnection is performed by the _mprshut command using a temporary command text file as standard input.  Because a disconnection may take a few seconds, a pause of 15 seconds executes before re-opening the query. The _connect-disconnect field will be 1 when the disconnected process is finished.

Copyright © 2005 Paul Guggenheim & Associates 27 DB-13: Understanding VSTs 27 DB Area Statistics  The _DBStatus and the _AreaStatus VSTs supply useful information about the database and database areas.

Copyright © 2005 Paul Guggenheim & Associates 28 DB-13: Understanding VSTs 28 DB Area Statistics  In program dbareastat.p, the size of the bi is monitored along with the total number of locks, the highest number of locks and highwater marks for database areas.  In V9, the multi-volume bi size is reported by dividing the high water mark blocks by the bi block size.

Copyright © 2005 Paul Guggenheim & Associates 29 DB-13: Understanding VSTs 29 Record Requests  Promon provides a tremendous amount of database and performance statistics.  By using VSTs, this data can be processed any way desired.

Copyright © 2005 Paul Guggenheim & Associates 30 DB-13: Understanding VSTs 30 Record Requests  For example, the program userio.p shows the amount of activity for requests vs. record reads per user and in summary.  The _UserIO table provides information on a per user basis for reading and writing to the database, before- image and after-image files. This information may be found on the Block Access screen (3) in promon.  The _ActSummary table provides summary information and some of its data may be found on the Activity screen (5) in promon.  Some useful information provided by _ActSummary is the number of checkpoints and database buffers flushed.

Copyright © 2005 Paul Guggenheim & Associates 31 DB-13: Understanding VSTs 31 Record Requests

Copyright © 2005 Paul Guggenheim & Associates 32 DB-13: Understanding VSTs 32 Table Statistics  Table statistics are available through VSTs but not through promon.  Statistics on the number of times a table was read, updated, created and deleted are kept.  Note that data that is undone does not reduce the corresponding statistic.  Unfortunately, there is nothing in VSTs that link user access to specific records in tables.  For example, to show which records were read by a given user would be useful for security or for application troubleshooting purposes.

Copyright © 2005 Paul Guggenheim & Associates 33 DB-13: Understanding VSTs 33 Table Statistics  The program tablestat.p is used show the tables with the highest number of reads.  The Refresh button may be pressed to show the latest data.  Tablestat.p uses the _TableStat VST.

Copyright © 2005 Paul Guggenheim & Associates 34 DB-13: Understanding VSTs 34 Buffer Status  One of the most important parameters to set is the database buffers parameter, –B.  Setting it too high can waste memory and could cause swapping.  Setting it too low can cause increased disk access and performance degradation.  The _BuffStatus VST can be used to measure the effectiveness of the –B parameter.

Copyright © 2005 Paul Guggenheim & Associates 35 DB-13: Understanding VSTs 35 Buffer Status  In buffstat.p, the program opens the _bfstatus record in the query and displays it to the screen when the Refresh button is pressed.  This is the same information that is shown in promon under R&D->1 (Status Displays)-> 7 (Buffer Status).

Copyright © 2005 Paul Guggenheim & Associates 36 DB-13: Understanding VSTs 36 Buffer Status  In buffstat.p, the program opens the _bfstatus record in the query and displays it to the screen when the Refresh button is pressed.  With the –B set at 500, notice that the total buffers is 502.  One extra buffer is for the Database Master Block.  The 2 nd block included is called the Index Anchor Block and is not used in V9.

Copyright © 2005 Paul Guggenheim & Associates 37 DB-13: Understanding VSTs 37 Buffer Status  If a long report is run, such as: for each registration: end. then the unused buffers become filled from the report.

Copyright © 2005 Paul Guggenheim & Associates 38 DB-13: Understanding VSTs 38 Setting Read Only Buffers  Question: How do we prevent all the buffers being used up by a report? Answer: Set the read only buffers on the client.  Two ways to do this: 1.At startup using the –Bp parameter 2.Updating the _MyConn-NumSeqBuffers field in the _MyConnection VST.

Copyright © 2005 Paul Guggenheim & Associates 39 DB-13: Understanding VSTs 39 Setting Read Only Buffers  Read only buffers (ROBs) are new to V9. The –Bp parameter specifies the number of read-only blocks a client may have.  ROBs are part of the total –B buffer pool, so that the remaining buffers are available for modified buffers.  Once a client has ROBs allocated to them, a large report’s records will stay confined to the ROBs.

Copyright © 2005 Paul Guggenheim & Associates 40 DB-13: Understanding VSTs 40 Setting Read Only Buffers  We will start a session with a –Bp = 64.  We will run a series of reports from the editor: for each student no-lock for each registration no-lock  The used buffers increases slightly, but then remains fixed.

Copyright © 2005 Paul Guggenheim & Associates 41 DB-13: Understanding VSTs 41 Setting Read Only Buffers  Next, we run updrobuf.p, and set the read only buffers equal to 0.  We then run the reports and notice that the used buffers equal to the total buffers.  The used buffers is a high water mark. It will not go down even though the buffers may be re-used.

Copyright © 2005 Paul Guggenheim & Associates 42 DB-13: Understanding VSTs 42 Customizing PRO*Tools Toolbar  A convenient place to put the VST programs you created is on the PRO*Tools Toolbar.

Copyright © 2005 Paul Guggenheim & Associates 43 DB-13: Understanding VSTs 43 Customizing PRO*Tools Toolbar  It is fairly easy to add your own tools to this toolbar.  Right-mouse-click on the toolbar and select Menu Bar. A pull-down menu bar will appear on the toolbar.  Select File->Customize… then press the Add button to add your program.  Select Run Persistent, Display on palette and supply an image.  Select “yes” to override protools.dat so that your tools will show up on every session.

Copyright © 2005 Paul Guggenheim & Associates 44 DB-13: Understanding VSTs 44 Customizing PRO*Tools Toolbar  Make sure that the PROPATH environment variable contains the directory where your VST programs are located.  Two include files are required in order to be compatible with the PRO*Tools toolbar.  _adetool.i – contains a single internal procedure called ADEPersistent, which prevents the Progress Editor from removing the instance when running other programs.  _runonce.i – prevents multiple instances of the tool to be run at the same time.

Copyright © 2005 Paul Guggenheim & Associates 45 DB-13: Understanding VSTs 45 Customizing PRO*Tools Toolbar  Each option also contains its own dynamic window and is parented to the PGA toolbar window.

Copyright © 2005 Paul Guggenheim & Associates 46 DB-13: Understanding VSTs 46 Acknowledgements  I would like to thank Dan Foreman for writing the Virtual System Tables Guide. It was very helpful in creating this presentation.

Copyright © 2005 Paul Guggenheim & Associates 47 DB-13: Understanding VSTs 47 Summary  VSTs provide 4GL access to information contained in promon.  Many useful reports and tools may be created.