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Updated on 2024-09-02 GMT+08:00
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PGXC_OBS_IO_SCHEDULER_PERIODIC_STATS

PGXC_OBS_IO_SCHEDULER_PERIODIC_STATS provides statistics on the number of requests and flow control information for different types of OBS I/O Scheduler requests, including read, write, and file operations. This system view is supported only by clusters of version 9.1.0 or later.

The first query result shows the statistics from the cluster startup to the query time, with detailed columns listed in the table below.

Table 1 PGXC_OBS_IO_SCHEDULER_PERIODIC_STATS columns

Column

Type

Description

node_name

name

Name of a CN or DN, for example, dn_6001_6002.

io_type

char

Type of I/O operation, including:

  • R: read
  • W: write
  • S: file operation

recent_throttled_req_num

int

Number of times flow control was applied between two query views.

total_throttled_req_num

int

Total number of times flow control was applied.

last_throttled_dur(s)

int8

Time interval since the last occurrence of flow control.

waiting_req_num

int

Number of queued requests currently waiting.

mean_tps

numeric(7,2)

Average TPS (transactions per second) between two query views.

mean_req_size(KB)

int8

Average length of requests between two query views, in KB.

mean_req_latency(ms)

int8

Average latency of requests between two query views, in ms.

max_req_latency(ms)

int8

Maximum latency of requests before two query views, in ms.

mean_bps(KB/s)

int8

Average read or write speed between two query views, in KB/s.

duration(s)

int

Time interval between two query views, in seconds.

Example

Run the SELECT * FROM pgxc_obs_io_scheduler_periodic_stats statement to query the view content. The following is an example of the query result: 
SELECT * FROM pgxc_obs_io_scheduler_periodic_stats;

  node_name   | io_type | recent_throttled_req_num | total_throttled_req_num | last_throttled_dur(s) | waiting_req_num | mean_tps | mean_req_size(KB) | mean_req_latency(ms) | max_req_latency(ms) | mean_bps(KB/s) | duration(s)
--------------+---------+--------------------------+-------------------------+-----------------------+-----------------+----------+-------------------+----------------------+---------------------+----------------+-------------
 dn_6001_6002 | S       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         155
 dn_6001_6002 | R       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         155
 dn_6001_6002 | W       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         155
 cn_5001      | S       |                        0 |                       0 |                     0 |               0 |      .03 |                 0 |                  207 |                 519 |              0 |         155
 cn_5001      | R       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         155
 cn_5001      | W       |                        0 |                       0 |                     0 |               0 |      .01 |                 0 |                  288 |                 288 |              0 |         155
(6 rows)

To display 0 before the decimal point in the value of mean_tps, execute set behavior_compat_options='display_leading_zero'.

Run the select * from pgxc_obs_io_scheduler_periodic_stats statement. The following information is displayed: 
SELECT * FROM pgxc_obs_io_scheduler_periodic_stats;

  node_name   | io_type | recent_throttled_req_num | total_throttled_req_num | last_throttled_dur(s) | waiting_req_num | mean_tps | mean_req_size(KB) | mean_req_latency(ms) | max_req_latency(ms) | mean_bps(KB/s) | duration(s)
--------------+---------+--------------------------+-------------------------+-----------------------+-----------------+----------+-------------------+----------------------+---------------------+----------------+-------------
 dn_6001_6002 | S       |                        0 |                       0 |                     0 |               0 |     0.36 |                 0 |                  132 |                 326 |              0 |         177
 dn_6001_6002 | R       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         177
 dn_6001_6002 | W       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         177
 cn_5001      | S       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         177
 cn_5001      | R       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         177
 cn_5001      | W       |                        0 |                       0 |                     0 |               0 |     0.00 |                 0 |                    0 |                   0 |              0 |         177
Parent topic: System Views