R8. Glossary
Diátaxis: Reference (a dictionary to look things up in) · Audience: operators / administrators ← Back to contents
Short definitions of the terms that come up often in this manual. For the concepts in more detail see E. Understanding the Concepts, and for how to judge a metric see E3. What the Metrics Mean.
Terms (Alphabetical)
| Term | Meaning |
|---|---|
| Agent | The collector attached to an instance that gathers performance data and sends it to the APM server. |
| Application group | The service-level unit bundling the instances that are meaningful to look at together. → E2.1 |
| Availability | The proportion of time the service responded normally (99.9%, for example). The core SLA metric. |
| Context selector | The tool at the top of the main area for narrowing the target by group, host, or instance. → R4 |
| Datasource (connection pool) | The bundle of connections the application borrows database connections from. When exhausted, requests wait. → H8 |
| Deadlock | The state where two or more threads wait on each other's locks and are stuck for good. |
| Error rate | The proportion of all requests that returned a 4xx or 5xx error (%). |
| Garbage collection (GC) | The JVM's work of clearing unused objects from the heap. A brief pause (STW) occurs while it cleans. → E3.2 |
| Heap | The JVM memory space where Java objects accumulate. |
| Instance | One process actually running (one WAS, one database broker, and so on). |
| Merge | The selector option deciding whether to combine several targets into one line or split them out individually. → H1 |
| Metaspace (non-heap) | The area outside the heap where class metadata accumulates. A leak from repeated redeployment causes an OOM. |
| Outlier | A value statistically far from the usual pattern. Repeated, it is a precursor to passing a threshold. |
| Response time | The time taken to handle one request (ms). |
| Sawtooth pattern | The normal shape where heap utilization rises and falls after GC, repeatedly. A flat line suggests a leak. → H7 |
| Thread dump | A snapshot of what every thread was doing at that moment. Used for deadlock and hang analysis. |
| Threshold | The level above which an event is raised. Two levels, WARN and CRITICAL. → H15 |
| Transaction | The handling flow of one user request (request → processing → response). → E2.2 |
| Waterfall | The screen laying out the segments of one transaction (database, external calls, and so on) as bars in time order. → T2 |
| Worker | The unit in which a web server (load balancer) handles requests. When exhausted, connections wait or are refused. |
Abbreviations
| Term | Meaning |
|---|---|
| APM | Application Performance Management/Monitoring. → E1 |
| APDEX | Application Performance Index. The score converting response time into user satisfaction (0 to 100). → E3.1 |
| CAS | The response handling process of a CUBRID broker. When saturated, database requests wait or fail. |
| CogentAI | The AI feature that analyses charts and events to suggest a likely cause and an action. → H14 |
| Full GC | The GC that cleans the whole heap. Its STW pause is large. |
| OOM (OutOfMemoryError) | The serious error where the JVM can no longer allocate memory because the heap is short. |
| SLA | Service Level Agreement. The promised service level (usually expressed as availability). → E3.3 |
| STW (stop-the-world) | The interval where the application pauses briefly, for GC or similar. |
| TPS | Transactions Per Second. The number of requests handled in one second (throughput). → E3.1 |
| T-Map | The heatmap scattering transactions by response time and time of day. Problems are read from the distribution. → H5 |