Accessing SAS Files through a SAS/SHARE Server

The following figure illustrates two client sessions that are accessing SAS files by using a SAS/SHARE server.

SAS Library Access through a SAS/SHARE Server

The SAS/SHARE server enables multiple clients to effectively share the same SAS file at the same time. In this context, “share” means to allow access by multiple clients to a different unit (for example, an observation) in the same SAS file. In the preceding figure, Client 1 can read from and write to observation 1, and Client 2 can read from and write to observation 2 in the same SAS file. Both clients can also read the same observation at the same time. However, only one client at a time can write to an observation.

The server enables client access to the lowest unit of the SAS library hierarchy through its powerful lock manager facility. Locks are applied in either of two ways:

A client might specify an explicit lock with a LOCK command or a LOCK statement.
A client operation might automatically submit a request for an implicit lock.

The SAS/SHARE server evaluates each incoming client request to access a specific SAS library unit (for example, a data library, a data set, or an observation) against a complex set of locking rules whose application seems transparent to clients. The server balances the client requests for access to data while ensuring the integrity of that data. The server grants permission to a qualifying client and denies a conflicting request. The denied client receives an informational message. For more information about server locking rules, see Locking SAS Data Objects. For information about the use of the LOCK command and the LOCK statement, see Locking Objects Explicitly (LOCK Statement), and Locking Explicitly in a SAS Window (LOCK Command).

CAUTION:

Although a SAS/SHARE server can effectively control multi-client access to a SAS library, independent direct access to the data from other SAS sessions or operating environments can interfere with the SAS/SHARE server.

Simultaneous and unregulated access to a common SAS library causes unpredictable results and possibly corrupt data. Your site policies should prohibit unregulated data access. Make sure that your data access policies are clearly communicated.