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Measures reported by R3BufferTest
This test reports statistics relating to the SAP R/3 server's buffers. The goal of buffer setting is to have a sufficiently large buffer to maintain a high hit rate and to do so with a low rate of swapping and a minimal effect on operating system paging. The test contains values for the following SAP buffers, sorted by application server:
| Name of the MTE |
Contents of the Buffer |
| Program |
Compiled SAP programs |
| Generic Key |
Wholly or partly buffered database tables |
| SingleRecord |
Individual records from utilized database tables |
| Screen |
Screen pages from ABAP programs |
| CUA |
Menus and pushbuttons from the ABAP screen pages |
| TableDefinition |
Table Definitions from the SAP R/3 Repository |
| FieldDescription |
Field descriptions from the SAP R/3 Repository |
| InitialRecords |
Initial record layout (initial values for the fields of a database segment) for a table |
| ShortNameTAB |
Combination of TTAB and FTAB buffers |
The measures made by this test are as
follows:
| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Directory_used |
The percentage usage of the directory (number of entries) |
Percent
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A buffer stores the results of the directory entry searches. This, in turn, significantly reduces the number of direct disk searches. If the value of this measure decreases, it indicates that directory entries are searched for directly from the disk. Since direct disk searches are expensive operations, this could lead to a marked degradation of the system performance. |
| Space_used |
The percentage of buffer storage space been used currently |
Percent
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Assigning adequate memory for the buffers ensures a high hit rate, but with low swapping rate and OS paging. However, allocating too much memory for the buffer will cause the OS to perform expensive paging. |
| Hit_ratio |
The percentage of database queries that were met from the buffer |
Percent
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In general, poor buffer quality means that a buffer is too small. If a buffer is too small, then the chances increase that requested objects (table entries, programs, and so on) will not be found in it. The result is a lower hit ratio, and, if the buffer is already full, increased swapping. To improve the hit ratio, increase the size of a buffer. |
| Swaps |
The rate of swaps due to a filled buffer |
Swaps/Min
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Swapping increases as requested objects force older objects out of the buffer. Increase the size of the buffer if the swap rate is very high and the hit ratio is low. |
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