The read row probes are triggered at a storage engine level each
time a row read operation occurs. These probes are specified
within each storage engine (as opposed to the
*row-start
probes which are in the storage
engine interface). These probes can therefore be used to monitor
individual storage engine row-level operations and performance.
Because these probes are triggered around the storage engine row
read interface, they may be hit a significant number of times
during a basic query.
read-row-start(database, table, scan_flag) read-row-done(status)
read-row-start
: Triggered when a row is read by the storage engine from the specifieddatabase
andtable
. Thescan_flag
is set to 1 (true) when the read is part of a table scan (that is, a sequential read), or 0 (false) when the read is of a specific record.read-row-done
: Triggered when a row read operation within a storage engine completes. Thestatus
returns 0 on success, or a positive value on failure.