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How to debug "Increase -L" error,record locking,transactions

900531-hjb01

INTRODUCTION: Date Last Modified: 6/26/90
=============

This Product Services Technical Support Knowledgebase entry details the
causes and corrective measures to take if you encounter PROGRESS errors
915 or 429. It explains record locking and scoping issues as related
to the size of PROGRESS transactions.


PROGRESS ERROR NUMBER: PROGRESS ERROR TEXT:
====================== ====================

429 (before version SYSTEM ERROR: Record Lock table is too
5 PROGRESS) small, Increase -L parameter


915 (version 5 PROGRESS Locktable overflow lock table size =
and above) (number)


POSSIBLE CAUSE OF ERROR:
========================

The application is locking more records than the server startup
parameter (-L) currently allows. If you do not specify -L as a startup
parameter on the PROGRESS SERVER (proserve command), PROGRESS sets the
default number of locks to 500.


The most likely reasons that PROGRESS is locking a large number of
records are:

1) The transaction is very large.

-OR-

2) The records are being held SHARE-LOCKed after the transaction
because the record scope has not ended.


DOES ERROR INDICATE CORRUPTION: IF SO, WHAT TYPE:
=============================== =================

NO N/A


CORRECTIVE MEASURES:
===================

Increasing the -L startup parameter on the PROGRESS SERVER (proserve
command) gets around the problem, but more records remain locked thus
creating a greater likelihood of other users attempting to access
locked records.


Running the procedure in single-user bypasses PROGRESS record-locking.
If your process involves a large transaction and you do not want to
exclude active users from updating locked records, consider running the
process in single-user, batch, or both at a time when users are not
actively updating records.


Making transactions smaller within your procedure locks fewer records
and avoids having to increase the lock table (-L) startup parameter.
One method of lowering the scope of your transaction is to put a DO
TRANSACTION: block directly around the statement that updates the
record. If the scope of the record you are updating is higher than the
scope of the transaction, however, PROGRESS holds on to a SHARE-LOCK
for each record until the end of the record scope. The RELEASE
statement allows you to explicitly release a SHARE-LOCKed record after
the statement which updates the database has occurred.


What is a record's scope? The block in which it was first referenced
in your procedure or in a calling procedure. Use the COMPILE with the
LISTING option to determine a record's scope. Note that any reference
to a record, before the first block in the program, scopes that record
to the procedure block.The procedure block does not end until program
end. Therefore record locks being held until the end of the record
scope are held for the duration of the program unless you explicitly
release the lock with the RELEASE statement.


What is transaction scope? The outermost block with transaction
properties that updates the database. Statements that update the
database include: UPDATE, CREATE, ASSIGN and SET. Blocks with
transaction properties include: FOR EACH, REPEAT, PROCEDURE, DO
TRANSACTION, a block that specifies EXCLUSIVE-LOCK and any block that
has the TRANSACTION keyword. Use the PROGRESS istrans.p procedure to
determine if there is already an active transaction in your procedure
(see next paragraph for details). Note that PROGRESS allows only
one active transaction at a time, so the next transaction that you
start in your procedure is actually a subtransation. Also note that if
you start a transaction in one procedure and it has not ended when you
call a sub-procedure, new transactions in the sub-procedure will also
be subtransactions.


ONLINE PROCEDURES OR UTILITIES:
===============================

You can run the debugging procedure istrans.p anywhere from within your
program to determine if there is a transaction active. To get a copy
of istrans.p (PROGRESS version 5 and above) go to the Procedure Library
from PROGRESS HELP and EXTRACT PROCEDURE istrans.p from the TOOLS
library. In PROGRESS versions prior to 5, RUN unpack.p from the
PROGRESS Editor and specify istrans.p as the procedure to unpack.


The Database Monitor - Option 4 Record Lock Table. The monitor
displays current record locks being held. (PROGRESS version 5 and after
only). See The PROGRESS System Administrator's Guide for information on
how to use this utility.


The COMPILE LISTING option gives information on where records and
transactions within your program are scoped.


REFERENCES TO WRITTEN DOCUMENTATION:
====================================

Programming Handbook - Chapter on Multi-user Applications


Programming Handbook - Chapter on Transactions


Programming Handbook - References to istrans.p in index


System Administration Guide - Chapter on the PROGRESS Monitor


Reference - COMPILE with LISTING option

Progress Software Technical Support Note # 3284