The onstat -g buf command displays buffer pool profile information.
Buffer pool page size: 2048 dskreads pagreads bufreads %cached dskwrits pagwrits bufwrits %cached 2652369545 3107084160 366802060932 99.28 87917396 1834297568 614184214 85.69 bufwrits_sinceckpt bufwaits ovbuff flushes 34873 5274275 0 7713 Fg Writes LRU Writes Avg. LRU Time Chunk Writes 0 0 -nan 29611228 Buffer pool page size: 16384 dskreads pagreads bufreads %cached dskwrits pagwrits bufwrits %cached 16802797 789997704 6102863013 99.72 211199321 1689594568 802506540 73.68 bufwrits_sinceckpt bufwaits ovbuff flushes 52158 19536628 0 7548 Fg Writes LRU Writes Avg. LRU Time Chunk Writes 0 0 -nan 211199321 Fast Cache Stats gets hits %hits puts 2851586101 2752172888 96.51 2050281903
| Option | Description |
|---|---|
| Buffer pool page size | Number of bytes in a page in the buffer pool being profiled |
| dskreads | Number of disk read operations performed to bring pages into this buffer pool. Each read operation reads one or more pages. |
| pagreads | Number of pages read from disk to this buffer pool |
| bufreads | Number of times a memory image for a page was read from this buffer pool |
| %cached | Percentage of page reads for this buffer pool that were satisfied by a cached page image (rather than having to perform a disk read). Computed as (bufreads - dskreads) / bufreads x 100. Higher percentages indicate better caching performance. |
| dskwrits | Number of disk write operations performed to write changed pages from this buffer pool back to disk. Each write operation writes one or more pages. |
| pagwrits | Number of pages written to disk from this buffer pool |
| bufwrits | Number of times a memory image of a page was written to in this buffer pool |
| %cached | Percentage of page writes for this buffer pool that were satisfied by a cached page image (rather than having to perform a disk write). Computed as (bufwrits - dskwrits) / bufwrits x 100. |
| bufwrits_sinceckpt | Number of times a memory image of a page was written to in this buffer pool since the last checkpoint |
| bufwaits | Number of times a thread had to wait for a lock on a buffer in this buffer pool. Higher numbers indicate more contention among multiple threads for mutually incompatible locks on the same pages. |
| ovbuff | Number of times a changed buffer from this buffer pool was written to disk specifically to create a free buffer to read another requested page. If the ovbuff value is high, it may indicate that the buffer pool is not large enough to hold the working set of pages needed by the applications using this buffer pool, which may lead to performance degradation from I/O thrashing. |
| flushes | Number of times the server performed a mass flush of all dirty buffers in the buffer pool. This can occur for a variety of reasons, including as part of checkpoint processing or if the buffer pool is running out of clean buffers despite normal LRU cleaning activity. |
| Fg Writes | Number of changed buffers from this buffer pool that were written to disk by a non-I/O flusher thread that was accessing the buffer. This number is a superset of ovbuff. In addition to the writes to service page faults counted by ovbuff, this value also includes foreground writes that are done by certain operations to maintain the consistency of database logs and reserved pages in order to guarantee correctness of crash recovery in special cases. |
| LRU Writes | Number of changed buffers from this buffer pool that were written to disk by an LRU cleaner thread. LRU cleaners are activated if the buffer pool exceeds the value specified in the lru_max_dirty field of the BUFFERPOOL configuration parameter or if foreground writes occur due to buffer pool overflows. |
| Avg. LRU Time | Average amount of time taken by an LRU cleaner thread to clean a single LRU chain. |
| Chunk Writes | Number of changed buffers that were written to disk by a chunk cleaning operation. Chunk cleaning writes out all changed buffers of a given chunk that are in the buffer pool. This is done in a variety of special circumstances that need to clean a large number of buffers quickly, such as checkpoint processing and fast recovery. |
| Fast Cache Stats | Statistics for the fast cache, which is a type of cache that reduces the time needed for accessing the bufferpool |
| gets | The number of times the server looked for a buffer in the fast cache |
| hits | The number of times that the server found the buffer it was searching for in the fast cache |
| %hits | The percentage of hits, which is hits*100/gets |
| puts | The number of times that the server inserted buffers inserted into the fast cache |
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