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Caché maintains a buffer pool - an in-memory cache of frequently referenced data blocks - to reduce the cost of fetching blocks from disk. By default, 16 KB is the memory allocated to the database cache. Close monitoring of the buffer pool is essential to determine the adequacy of the memory allocation to the cache. By increasing the memory allocation, administrators can considerably increase cache hits, reduce disk accesses, and consequently, save the processing overheads. The CacheBufferTest monitors the usage of the buffer pool of every database in the Cache database server. In the process, the test also observes the behavior of the interactive and batch buffer queues. Any Cache process created in the Cache database is set to execute either in the 'interactive' or in the 'batch' mode. Since an 'interactive' process expects user inputs, it has to be run in the foreground and is also, resource-intensive. A 'batch' process on the other hand can only be run in the background, and uses less resources.

Measurement	Description	Measurement Unit	Interpretation
Buffer_size	The current size of the buffer	Bytes	A well-tuned environment is one where the buffer is sufficiently sized. A low value of this measure is unhealthy, as light weight buffers force a large number of direct disk accesses causing the database to incur excessive processing overheads.
Buffer_count	The number of buffers of buffer size	Number
Batch_queue_offset	The current offset to the start of the LRU (least recently used) queue.	Number
Interactive_buffers	The number of buffers currently in the interactive portion of the LRU ueue	Number
Max_interactive_buffers	The maximum number of buffers currently in the interactive portion of the LRU queue	Number
Requeue_limit_interactive	The threshold for requeuing an interactive buffer	Number
Requeue_limit_batch	The threshold for requeueing a batch buffer	Number
Interactive_write_queue	The number of interactive buffers in the current write cycle	Number
Buffers_write_queue	The number of buffers requeued in the batch LRU queue	Number
Write_queue_wait_max	The threshold for waking the interactive write daemon	Number
Available_interactive_buffers	The current number of available interactive buffers	Number	Ideally, this value should be high. If the value is low, then the buffer might be unable to serve all interactive job requests, thus forcing direct disk accesses. This could ultimately increase processing overheads.
Min_interactive_buffers	The minimum number of buffers in the interactive portion of the LRU queue	Number
Buffer_usage	The percentage of buffer size that is currently utilized	Percent	Ideally, this value should be high. Low buffer usage is indicative of high direct disk usage.