SAS Safety Scalable Performance Data Server 4.5 Manual Do Utilizador

PROC PRINT data=a_noher.admins_table ;
  title 'without libaclinher'
run ;

Dynamic locking is an SPD Server feature that allows multiple users concurrent access to
SPD Server tables. The tables can be concurrently accessed by multiple users for reading
and writing, while maintaining the integrity of the table contents. When dynamic locking
is enabled, users can insert, append, delete, and update the contents of an SPD Server table
while doing concurrent reads on the table.

Dynamic locking is enabled or disabled at the domain level. All tables stored within the
domain are subject to the enabled or disabled state of the dynamic locking feature. The
DYNLOCK= statement should be used in libnames.parm file domain declarations.

How is dynamic locking different from SPD Server record-level locking? Clients that use
dynamic locking connect to a separate SPD user proxy process for each LIBNAME
connection in the domain. In SPD Server record-level locking, all clients share the same
record-level locking proxy process.

SPD Server uses the dynamic locking feature to alleviate some of the problems and
limitations that occur with record-level locking.

The dynamic locking method of using separate proxy processes instead of a single record-
level proxy distributes resource allocations, which decreases the probability of a single
proxy process hitting resource limits. Dynamic locking also removes a single record-level
locking point of failure for the record-level proxy.

If there is a failure in an SPD Server user proxy when dynamic locking is being used, only
the client that is connected to that proxy is affected. If there is a failure in an SPD Server
record-level proxy, it all client connections are affected.

Dynamic locking can also provide better performance than record-level locking. Dynamic
locking has performance advantages over record-level locking when concurrent read and
write access to a table is required. This is due to the more distributed processing and
parallelism of that occurs when multiple SPD Server user proxies are used. The
performance benefit depends on the opportunities for parallelism and should be measured
on a case-by-case basis.

In order to use dynamic locking, SPD Server tables must be part of a named SPD Server
domain. When dynamic locking is enabled for a domain, all of the SPD Server users that
access tables in that domain will automatically use dynamic locking. The SPD Server
clients do not need to set any additional parameters to take advantage of the domain's
dynamic locking benefits.

When SPD Server proxy processes receive concurrent update, append, insert, and delete
commands, they are sequentially queued and then executed in order of arrival. Only one
update operation is performed on a table at any one time. Read requests can be executed
at any point while an update is in progress. Read requests get the most recent information
that is available in the table, based on the last physical update to disk.