Hot Spot - Contention Point

Key Characteristics

• • Resource-Specific: Can manifest as contention for CPU cycles, I/O channels, memory, data sets, specific records in a database (e.g., DB2, IMS), enqueues, latches, or critical sections of application code.
  • Performance Impact: Directly contributes to increased transaction response times, reduced throughput, CPU wait states, and overall system inefficiency due to tasks waiting for resource availability.
  • Dynamic Nature: Hot spots are not static; they can shift based on workload patterns, time of day, application changes, or system configuration, requiring continuous monitoring.
  • Detection Methods: Identified through performance monitoring tools like RMF (Resource Measurement Facility), SMF (System Management Facilities) records, specialized database monitors (e.g., DB2 PM, IMS PA), and application-level tracing.
  • Serialization: Often involves serialization mechanisms (e.g., ENQs, LATCHes, database locks) to maintain data integrity, which, when overused or held too long, becomes a contention point.

Use Cases

• • Database Row/Page Contention: Multiple CICS transactions or batch jobs attempting to update the same row or page in a DB2 table or IMS segment concurrently, leading to lock waits and transaction delays.
  • Shared Data Set Access: High read/write activity on a critical VSAM KSDS or sequential data set by numerous batch jobs or online regions, causing I/O queueing and ENQ contention.
  • Operating System Control Blocks: Frequent access and updates to a core z/OS control block by various system components or user tasks, leading to LATCH contention within the operating system kernel.
  • Application Code Critical Section: A poorly designed COBOL program segment that acquires and holds a global ENQ or a database lock for an extended period while performing non-critical operations, blocking other tasks.
  • CPU Bottleneck: A specific CPU or logical partition (LPAR) where a single, highly CPU-intensive task or a group of tasks consistently consumes a large percentage of available processing power, starving other workloads.

Related Concepts