DB2 data sharing
A way of running several DB2 subsystems on different systems of a sysplex so that they all share the same databases.
Also written data sharing, data sharing group, data sharing member, group buffer pool, GBP
In DB2 data sharing, several DB2 subsystems, called members, form a data sharing group. Each member runs on a different z/OS system in a sysplex, and all of them read and update the same databases at the same time.
The coupling facility makes this safe. A lock structure there records locks for the whole group, so two members never change the same data at once. Group buffer pools hold changed pages so every member sees the latest version. A shared communications area keeps the members informed about each other.
The main benefit is availability. If one member or its system fails, or is stopped for maintenance, the other members keep working with the same data, and applications can be routed to them. It also lets a site add capacity by adding members.
For an application programmer, data sharing is mostly invisible: SQL works the same way. You may notice it in names, since each member has its own subsystem ID within the group, and in performance work, where sharing adds some overhead.
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- DB2 for z/OSIBM's relational database on the mainframe, where a great deal of the world's banking and insurance data is stored.
- SysplexA group of mainframe systems joined together so they behave as one, sharing work and data so that no single failure stops the service.
- Coupling facilityA special LPAR that holds shared information for all the systems in a sysplex, so they can work on the same data at the same time.
- Buffer poolAn area of memory where DB2 keeps recently used pages of data and indexes, so it does not have to read them from disk each time.
- XCFCross-system coupling facility: the part of z/OS that lets the systems in a sysplex talk to each other and know which of them are working.