OpenEdge Data Management: DataServer for Microsoft SQL Server

Initial Programming Considerations
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If the client application does not specify NO-WAIT, then the application automatically loops back
to the server in an internal wait mode and retries record access. It continues to do so until the
Lock Timeout period set on the client (–lkwtmo parameter specified in seconds) is exceeded. If
this wait period is exceeded without being able to successfully access the server resource, the
process times out, the wait is canceled and the client raises a stop condition.
When NO-WAIT is unspecified, the client consistently returns to the server to retry access to the
locked resource. If NO-ERROR is also unspecified, then during the Lock Timeout period
(-lkwtmo) a resource wait dialog box continues to be displayed to the user. It allows the user to
select cancel from the dialog to end the wait period. If the user does not cancel and the –lkwtmo
period has not been exceeded, the client performs constant retries and multiple round trips to the
server. This constant re-cycling, especially during a period of high resource contention, can be
normalized by setting a small timeout period on the server in which to handle lock conditions
before returning timeouts to the client application. The server wait period is set through the
PRGRS_NATIVE_LOCKWAIT –Dsrv connection parameter. The disadvantage to setting this
parameter to a non-zero value is that the client application is blocked for the timeout period set
on the server. This may produce some amount of server-bound latency that should be
considered when setting the number of milliseconds for this option. However, if the server is
able to complete the resource request in the server timeout period, the resource is returned to the
client immediately and the application unblocks. Therefore, the advantage of setting a non-zero
server timeout is that the server is given the opportunity to resolve record access without further
round trips from the client repeatedly request the same resource. A nonzero value may be
especially useful during periods of high contention and may increase the overall efficiency of
the DataServer application. Progress recommends a nominal but non-zero setting for the
number of milliseconds in most cases. Evaluate your average contention for resources in setting
this value for your own application.
The PRGRS_NATIVE_LOCKWAIT –Dsrv option permits an application to set a maximum time
threshold that the server will block the application waiting to fulfill a resource request that is
locked. When the server waits for the resource longer than the PRGRS_NATIVE_LOCKWAIT number
of milliseconds, control is returned to the client application which then handles the lock
condition as described earlier. As the PRGRS_NATIVE_LOCKWAIT time is increased, the number
of retries from the client within the –lkwtmo period is decreased (assuming NO-WAIT is
unspecified).
The PRGRS_NATIVE_LOCKWAIT setting will affect all transactions for all connections to the
foreign data source for a given application session. This includes read-only connections,
stored-procedure connections, and transactions on the sequences connection.
Note: Setting the PRGRS_NATIVE_LOCKWAIT is equivalent to setting the “LOCK_TIMEOUT”
value natively in MS SQL Server.