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 specified filepath
, reading the
specified number of bytes
. The
mem_used
and mem_avail
indicate 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 of bytes
, 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. The
mem_used
and mem_avail
indicate 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 specified filepath
,
reading the specified number of bytes
.
The mem_used
and
mem_avail
indicate 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 of bytes
, to the index file from
the keycache.
keycache-write-done
— triggered
when the keycache write operation has completed. The
mem_used
and mem_avail
indicate memory currently used by the keycache and the
amount of memory available within the keycache.
User Comments
Add your own comment.