PGXC_OBS_IO_SCHEDULER_STATS

Updated on 2024-12-18 GMT+08:00

View PDF

PGXC_OBS_IO_SCHEDULER_STATS displays the latest real-time statistics about read/write requests of the OBS I/O Scheduler. This system view is supported only by clusters of version 9.1.0 or later.

**Table 1** PGXC_OBS_IO_SCHEDULER_STATS columns
Column	Type	Description
node_name	text	Node name.
io_type	char	Type of I/O operation, including: r: read. w: write. s: file operation.
current_bps	int8	Current bandwidth rate, in KB/s.
best_bps	int8	Best bandwidth rate achieved recently, in KB/s.
waiting_request_num	int	Number of queued requests currently waiting.
mean_request_size	int8	Average length of requests processed recently, in KB.
total_token_num	int	Total number of I/O tokens.
available_token_num	int	Number of available I/O tokens.
total_worker_num	int	Total number of working threads.
idle_worker_num	int	Number of idle working threads.

Example

Query statistics about read requests of OBS I/O Scheduler on each node:

SELECT * FROM pgxc_obs_io_scheduler_stats WHERE io_type = 'r' ORDER BY node_name;

  node_name   | io_type | current_bps | best_bps | waiting_request_num | mean_request_size | total_token_num | available_token_num | total_worker_num | idle_worker_num
--------------+---------+-------------+----------+---------------------+-------------------+-----------------+---------------------+------------------+-----------------
 dn_6001_6002 | r       |       26990 |    26990 |                   0 |               215 |              18 |                  16 |               12 |              10
 dn_6003_6004 | r       |       21475 |    21475 |                  10 |               190 |              30 |                  30 |               20 |              20
 dn_6005_6006 | r       |       12384 |    12384 |                  36 |               133 |              30 |                  27 |               20 |              17

According to the result, this is a snapshot of the statistics at a certain time point when the current I/O scheduler reads I/Os. At this time, the bandwidth is increasing, and current_bps is equal to best_bps. Take dn_6003_6004 as an example. You can see that there are queuing requests on the current DN. The value of total_token_num is the same as that of available_token_num, indicating that the I/O scheduler has not started to process these requests when the view is queried.

Wait for a while and initiate the query again.

SELECT * FROM pgxc_obs_io_scheduler_stats WHERE io_type = 'r' ORDER BY node_name;

  node_name   | io_type | current_bps | best_bps | waiting_request_num | mean_request_size | total_token_num | available_token_num | total_worker_num | idle_worker_num
--------------+---------+-------------+----------+---------------------+-------------------+-----------------+---------------------+------------------+-----------------
 dn_6001_6002 | r       |       13228 |    26990 |                   0 |               609 |              18 |                  18 |               12 |              12
 dn_6003_6004 | r       |       15717 |    21475 |                   0 |               622 |              30 |                  30 |               20 |              20
 dn_6005_6006 | r       |       18041 |    21767 |                   0 |               609 |              30 |                  30 |               20 |              20

When the queue is empty and the value of available_token_num is equal to that of total_token_num, it indicates that the I/O scheduler has finished processing all requests and there are no new requests in line. The current_bps value is not 0 because it represents the average bandwidth (in bit/s) over a three-second period. Therefore, the displayed value reflects the data from three seconds ago.

After a short period of time, the query result is as follows. The value of current_bps changes to 0.

SELECT * FROM pgxc_obs_io_scheduler_stats WHERE io_type = 'r' ORDER BY node_name;

  node_name   | io_type | current_bps | best_bps | waiting_request_num | mean_request_size | total_token_num | available_token_num | total_worker_num | idle_worker_num
--------------+---------+-------------+----------+---------------------+-------------------+-----------------+---------------------+------------------+-----------------
 dn_6001_6002 | r       |           0 |    26990 |                   0 |               609 |              18 |                  18 |               12 |              12
 dn_6003_6004 | r       |           0 |    21475 |                   0 |               622 |              30 |                  30 |               20 |              20
 dn_6005_6006 | r       |           0 |    21767 |                   0 |               609 |              30 |                  30 |               20 |              20

Parent topic: System Views

Previous topic: PGXC_NODE_STAT_RESET_TIME

Next topic: PGXC_OBS_IO_SCHEDULER_PERIODIC_STATS