2019-01-31 11:22:47 | 作者: 昆卉 | 标签: 内存,答案 | 浏览: 6110
Memory area with a set (configurable) size that belongs to a work process.
For technical reasons， the roll area is always the first memory available to use for a work process. Only afterwards can extended memory be requested.
When the context of a work process changes， the data is copied from the roll area to a common resource known as the roll file. To prevent repeated copying， another roll buffer is located in between， which is part of the shared memory
Allocation of memory for the current internal session by transferring pages out of memory， similarly to operating system paging. SAPs memory management concept currently limits SAP Paging to cases where the ABAP commands EXTRACT and EXPORT... TO MEMORY... are used.
If the extended memory is fully occupied， or the limit for the work process has been exceeded， private memory is assigned to the work process. This is known as private memory because it is specific to the process， and the user context can no longer be processed by a different work process (PRIV mode).
ABAP扩展内存 - extended memory
User context is stored in the extended memory (EM) to enable fast context change . Depending on the operating system， how SAP implements EM addressing/mapping is different.
When the context is changed， the user context is not copied as with the roll area. Instead it is allocated to alternating work processes by mapping operations which results in a faster context change because less data is copied and mapping an extended area is not work-intensive. The result is low CPU usage and shorter access times.
SAP dispatcher is responsible for the following principle tasks:
1. Initialization， reading profile parameters， starting work processes and logging on to the message server
2. Evenly distributing the transaction load across work processes
3. Connecting to the GUI layer
4. Organizing communication processes