IOS_STATUS

The IOS_STATUS view is used to display the performance status of the I/O thread pool responsible for read-ahead for a recent period of time, including IOSCtl dispatch requests, I/O latency/bandwidth, queue backlog, and other metrics. When the main query thread I/O latency is very high or the cache hit rate is low, users or developers can visualize the performance of the read-ahead thread pool to help locate the problem.

Table 1 IOS_STATUS fields

Name	Type	Description
ios_worker_num	Int4	Current number of I/O thread pool ios_workers
io_requests	Int8	Total number of pre-read requests received by the thread pool
io_dispatched	Int8	Total number of pre-read requests dispatched by the thread pool to ios_worker
avg_io_size_blks	Int4	Average number of 8K pages included in each pre-read request
avg_io_request_latency_history	Int4	Average total latency of all historical pre-read requests (total time from start of entry into the IOSCtl queue to completion of ios_worker processing), in microseconds
avg_io_latency_history	Int4	Historical average I/O latency (time for I/O to read the disk) for all pre-read requests, in microseconds
avg_io_request_latency_ps	Int4	Average total latency of all pre-read requests in the last 1 second, in microseconds
avg_io_latency_ps	Int4	Average I/O latency of all pre-read requests in the last 1 second, in microseconds
blks_read_ps	Int4	Total number of 8K pages read in the last 1 second
io_read_ps	Int4	Total number of disks read in the last 1 second
io_queue_depth	Int4	The current queue depth of IOSCtl
ring_buff_mem	Int4	Current size of the memory that manages the pre-read ring buff data structure, in bytes