The keycache probes are triggered when using the index key cache used with the MyISAM storage engine. Probes exist to monitor when data is read into the keycache, cached key data is written from the cache into a cached file, or when accessing the keycache.
Keycache usage indicates when data is read or written from the index files into the cache, and can be used to monitor how efficient the memory allocatd to the keycache is being used. A high number of keycache reads across a range of queries may indicate that the keycache is too small for size of data being accessed.
keycache-read-start(filepath, bytes, mem_used, mem_free) keycache-read-block(bytes) keycache-read-hit() keycache-read-miss() keycache-read-done(mem_used, mem_free) keycache-write-start(filepath, bytes, mem_used, mem_free) keycache-write-block(bytes) keycache-write-done(mem_used, mem_free)
When reading data from the index files into the keycache, the
process first initializes the read operation (indicated by
keycache-read-start), then loads blocks of
data (keycache-read-block), and then the read
block is either matches the data being identified
(keycache-read-hit) or more data needs to be
read (keycache-read-miss). Once the read
operation has completed, reading stops with the
keycache-read-done.
Data will be read from the index file into the keycache only when the specified key is not aleady within the keycache.
keycache-read-start: Triggered when the keycache read operation is started. Data is read from the specifiedfilepath, reading the specified number ofbytes. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.keycache-read-block: Triggered when the keycache reads a block of data, of the specified number ofbytes, from the index file into the keycache.keycache-read-hit: Triggered when the block of data read from the index file matches the key data requested.keycache-read-miss: Triggered when the block of data read from the index file does not match the key data needed.keycache-read-done: Triggered when the keycache read operation has completed. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.
Keycache writes occur when the index information is updated
during an INSERT, UPDATE,
or DELETE operation, and the cached key
information is flushed back to the index file.
keycache-write-start: Triggered when the keycache write operation is started. Data is written to the specifiedfilepath, reading the specified number ofbytes. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.keycache-write-block: Triggered when the keycache writes a block of data, of the specified number ofbytes, to the index file from the keycache.keycache-write-done: Triggered when the keycache write operation has completed. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.