Hierarchy
SAP_BASIS (Software Component) SAP Basis Component⤷
BC-VMC (Application Component) Virtual Machine Container⤷
SVMCRT_ADMIN (Package) VMC Administration and Monitoring
Basic Data
| Data Element | SVMCRT_PROF_SGC_REASON |
| Short Description | Shared GC Statistics: Reason for the Garbage Collection |
Data Type
| Category of Dictionary Type | Direct Type Entry | |
| Type of Object Referenced | No Information | |
| Domain / Name of Reference Type | ||
| Data Type | CHAR | Character String |
| Length | 40 | |
| Decimal Places | 0 | |
| Output Length | 40 | |
| Value Table |
Further Characteristics
| Search Help: Name | ||
| Search Help: Parameters | ||
| Parameter ID | ||
| Default Component name | ||
| Change document | ||
| No Input History | ||
| Basic direction is set to LTR | ||
| No BIDI Filtering |
Field Label
| Length | Field Label | |
| Short | 5 | Reas. |
| Medium | 10 | Reason |
| Long | 15 | Reason |
| Heading | 20 | Reason |
Documentation
Definition
The following reasons can be specified for a shared VM garbage collection (GC):
- "Explicit shared GC": The shared GC was requested by a Java program.
- "Shared allocation failed": The memory request for a shared VM object failed. This forced the shared GC cycle and the wait for it to end. Then the memory was requested again.
- "Shared forced quota exceeded": The shared GC was forced because the percentage of VMs specified to contribute to the GC was reached. Once this quota is reached the shared GC run is forced to end even though the trigger (for example, a local VM full GC) for it would normally not have been sufficient.
- "Shared watermark exceeded": The shared GC was forced because more shared VM memory was occupied than defined in the configuration parameter "sharedWaterMark". This criticial watermark is specified as a percentage of the size of "Shared Pool". Reaching the watermark has no effect if a shared GC cycle has already started.
- "Shared GC statistic dump": The shared GC was triggered so that a set of shared GC statistics explicitly requested could be recorded.
- "Unknown reason": None of the above-mentioned events triggered this shared GC.
Use
Dependencies
Before a shared GC is triggered due to "shared allocation failed", the criterion for a "shared watermark" should have been met. That is, the critical watermark in the shared VM memory should be exceeded, thus forcing a shared GC.
The percentage defined in configuration parameter "sharedForceQuota" of VMs that need to have made their contribution to a shared GC cycle has the job of preventing a shared GC cycle from remaining open for too long because of a small number of inactive VMs. Long shared GC cycles are not desirable, as the memory for shared VM objects that are created or used at the same time as a shared GC cycle cannot be won back again.
The purpose of the watermark defined in configuration parameter "sharedWaterMark" is to force shared GC cycles before the shared VM memory is exhausted. This allows you to avoid wait states for VMs. However, it is not possible to guarantee that so much memory space is always available.
Example
History
| Last changed by/on | SAP | 20130604 |
| SAP Release Created in | 710 |
