SAS/ACCESS 9.2 for Relational Databases: Reference, Fourth Edition

530 How and When Connections Are Made 4 Chapter 16programs to connect to DB2 and to use DB2 for SQL statements and commands.SAS/ACCESS Interface to DB2 under z/OS uses the attachment facilities to establishand control its connections to the local DB2 subsystem. DB2 allows only one connectionfor each task control block (TCB), or task. SAS and SAS executables run under oneTCB, or task.The DB2 LIBNAME statement enables SAS users to connect to DB2 more than once.Because the CAF and RRSAF allow only one connection per TCB, SAS/ACCESSInterface to DB2 under z/OS attaches a subtask for each subsequent connection that isinitiated. It uses the ATTACH, DETACH, POST, and WAIT assembler macros to createand communicate with the subtasks. It does not limit the number of connections/subtasks that a single SAS user can initiate. This image illustrates how the DB2engine works.Display 16.1Design of the DB2 EngineHow and When Connections Are MadeSAS/ACCESS Interface to DB2 under z/OS always makes an explicit connection tothe local DB2 subsystem (SSID). When a connection executes successfully, a thread toDB2 is established. For each thread’s or task’s connection, DB2 establishesauthorization identifiers (AUTHIDs).SAS/ACCESS Interface to DB2 under z/OS determines when to make a connection toDB2 based on the type of open mode (read, update, or output mode) that a SASapplication requests for the DB2 tables. Here is the default behavior:3 SAS/ACCESS Interface to DB2 under z/OS shares the connection for all openingsin read mode for each DB2 LIBNAME statement3 SAS/ACCESS Interface to DB2 under z/OS acquires a separate connection to DB2for every opening in update or output mode.You can change this default behavior by using the CONNECTION= option.Several SAS applications require SAS/ACCESS Interface to DB2 under z/OS to querythe DB2 system catalogs. When this type of query is required, SAS/ACCESS Interfaceto DB2 under z/OS acquires a separate connection to DB2 in order to avoid contentionwith other applications that are accessing the DB2 system catalogs. See “AccessingDB2 System Catalogs” on page 532 for more information.The DEFER= LIBNAME option also controls when a connection is established. TheUTILCONN_TRANSIENT= also allows control of the utility connection—namely,whether it must stay open.