MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4
This table provides information regarding the latency of disk operations for NDB Cluster Disk Data tablespaces.
The pgman_time_track_stats table contains the
following columns:
node_id
Unique node ID of this node in the cluster
block_number
Block number (from blocks
table)
block_instance
Block instance number
upper_bound
Upper bound
page_reads
Page read latency (ms)
page_writes
Page write latency (ms)
log_waits
Log wait latency (ms)
get_page
Latency of get_page() calls (ms)
The read latency (page_reads column) measures
the time from when the read request is sent to the file system
thread until the read is complete and has been reported back to
the execution thread. The write latency
(page_writes) is calculated in a similar
fashion. The size of the page read to or written from a Disk
Data tablespace is always 32 KB.
Log wait latency (log_waits column) is the
length of time a page write must wait for the undo log to be
flushed, which must be done prior to each page write.