The X/Open DTP model assumes an understanding of certain terms.
transaction – a whole unit of work consisting of one or more computational tasks. Most often, a transaction’s tasks manipulate shared resources.
committed transaction – a completed transaction whose changes to any shared resources are permanent.
rolled-back transaction – a complete transaction whose changes to any shared resources are nullified.
ACID test – the test of a true transaction; to pass, the transaction must exhibit the following properties:
Atomicity – all or none of the results of the transaction take effect.
Consistency – if a transaction is rolled back, all resources that the transaction affected return to the state they were in prior to the transaction’s execution.
Isolation – a transaction’s results are visible only to that transaction until the transaction commits.
Durability – permanent resource changes resulting from commitment survive subsequent system failures.
transaction processing – a system of coordinating the transactions that multiple users perform on shared, centralized resources.
distributed transaction processing – a transaction processing model in which the shared resources are located at distinct physical sites on a computer network.
local transaction – a transaction that affects data in a single database and whose tasks a single resource manager performs. See “Overview of the X/Open DTP model” for a definition of resource managers.
global transaction – a transaction that spans more than one database and multiple resource managers.
transaction branch – a portion of the work that makes up a global transaction.
transaction identifier – an identifier that a TM assigns to a transaction. The transaction monitor uses the transaction identifier to coordinate all activity related to a global transaction. The resource manager uses the global identifier to match the recoverable tasks it performed for the transaction.
recovery – the process of bringing a transaction processing system into a consistent state after a failure. Specifically, this means resolving transactions left in a noncommitted state.
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