This line displays information about the main buffer cache.
Main I: L331224/P22 O: D25967/P7805 C:D0
Item |
Description |
|---|---|
Main: I: L# |
Number of logical file reads. |
P# |
Number of physical file reads. |
O: D# |
Number of times a buffer was destroyed. |
P# |
Number of physical writes. |
C: D# |
Buffer manager data compression ratio. This is the total number of bytes eligible for compression minus number of bytes used after compression divided by total number of bytes eligible for compression times 100. In other words, it tells how much data was compressed (what percentage it is of its uncompressed size). The larger the number, the better. Only certain data blocks are eligible for compression. Eligible blocks include indexes, (90-95% of a database) and Sort sets. This reflects only data compression techniques used by the buffer manager. Other data compression may take place before data reaches the buffer manager, so the total data compression may be higher. |
In general, assuming the buffer cache is full, you should have between 10 and 1000 logical reads per physical read. A lower value indicates excessive thrashing in the buffer manager. More than 1000 times larger can indicate that you may be overallocating memory to your buffer cache. If either of these conditions exists, see Performance and Tuning Guide for information on setting buffer cache size or using the IQ performance monitor.
