CPU usage throttling v16
EDB Resource Manager uses CPU throttling to keep the aggregate CPU usage of all processes in the group within the limit specified by the cpu_rate_limit parameter. A process in the group might be interrupted and put into sleep mode for a short time to maintain the defined limit. When and how such interruptions occur is defined by a proprietary algorithm used by EDB Resource Manager.
To control CPU use of a resource group, set the cpu_rate_limit resource type parameter.
Set the
cpu_rate_limitparameter to the fraction of CPU time over wall-clock time to which the combined, simultaneous CPU usage of all processes in the group must not exceed. The value assigned tocpu_rate_limitis typically less than or equal to 1.On multicore systems, you can apply the
cpu_rate_limitto more than one CPU core by setting it to greater than 1. For example, ifcpu_rate_limitis set to 2.0, you use 100% of two CPUs. The valid range of thecpu_rate_limitparameter is 0 to 1.67772e+07. A setting of 0 means no CPU rate limit was set for the resource group.When the value is multiplied by 100, you can also interpret the
cpu_rate_limitas the CPU usage percentage for a resource group.
Setting the CPU rate limit for a resource group
Use the ALTER RESOURCE GROUP command with the SET cpu_rate_limit clause to set the CPU rate limit for a resource group.
In this example, the CPU usage limit is set to 50% for resgrp_a, 40% for resgrp_b, and 30% for resgrp_c. This means that the combined CPU usage of all processes assigned to resgrp_a is maintained at approximately 50%. Similarly, for all processes in resgrp_b, the combined CPU usage is kept to approximately 40%, and so on.
edb=# ALTER RESOURCE GROUP resgrp_a SET cpu_rate_limit TO .5; ALTER RESOURCE GROUP edb=# ALTER RESOURCE GROUP resgrp_b SET cpu_rate_limit TO .4; ALTER RESOURCE GROUP edb=# ALTER RESOURCE GROUP resgrp_c SET cpu_rate_limit TO .3; ALTER RESOURCE GROUP
This query shows the settings of cpu_rate_limit in the catalog:
edb=# SELECT rgrpname, rgrpcpuratelimit FROM edb_resource_group;
rgrpname | rgrpcpuratelimit ----------+------------------ resgrp_a | 0.5 resgrp_b | 0.4 resgrp_c | 0.3 (3 rows)
Changing the cpu_rate_limit of a resource group affects new processes that are assigned to the group. It also immediately affects any currently running processes that are members of the group. That is, if the cpu_rate_limit is changed from .5 to .3, currently running processes in the group are throttled downward so that the aggregate group CPU usage is near 30% instead of 50%.
To show the effect of setting the CPU rate limit for resource groups, the following psql command-line examples use a CPU-intensive calculation of 20000 factorial (multiplication of 20000 * 19999 * 19998, and so on) performed by the query SELECT 20000!.
The resource groups with the CPU rate limit settings shown in the previous query are used in these examples.
Example: Single process in a single group
This example shows that the current process is set to use resource group resgrp_b. The factorial calculation then starts.
edb=# SET edb_resource_group TO resgrp_b; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- resgrp_b (1 row) edb=# SELECT 20000!;
In a second session, the Linux top command is used to display the CPU usage under the %CPU column. Because the top command output periodically changes, it represents a snapshot at an arbitrary point in time:
$ top top - 16:37:03 up 4:15, 7 users, load average: 0.49, 0.20, 0.38 Tasks: 202 total, 1 running, 201 sleeping, 0 stopped, 0 zombie Cpu(s): 42.7%us, 2.3%sy, 0.0%ni, 55.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0 Mem: 1025624k total, 791160k used, 234464k free, 23400k buffers Swap: 103420k total, 13404k used, 90016k free, 373504k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 28915 enterpri 20 0 195m 5900 4212 S 39.9 0.6 3:36.98 edb-postgres 1033 root 20 0 171m 77m 2960 S 1.0 7.8 3:43.96 Xorg 3040 user 20 0 278m 22m 14m S 1.0 2.2 3:41.72 knotify4 . . .
The row where edb-postgres appears under the COMMAND column shows the psql session performing the factorial calculation. The CPU usage of the session shown under the %CPU column is 39.9, which is close to the 40% CPU limit set for resource group resgrp_b.
By contrast, if the psql session is removed from the resource group and the factorial calculation is performed again, the CPU usage is much higher.
edb=# SET edb_resource_group TO DEFAULT; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- (1 row) edb=# SELECT 20000!;
Under the %CPU column for edb-postgres, the CPU usage is now 93.6, which is significantly higher than the 39.9 when the process was part of the resource group:
$ top top - 16:43:03 up 4:21, 7 users, load average: 0.66, 0.33, 0.37 Tasks: 202 total, 5 running, 197 sleeping, 0 stopped, 0 zombie Cpu(s): 96.7%us, 3.3%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0 Mem: 1025624k total, 791228k used, 234396k free, 23560k buffers Swap: 103420k total, 13404k used, 90016k free, 373508k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 28915 enterpri 20 0 195m 5900 4212 R 93.6 0.6 5:01.56 edb-postgres 1033 root 20 0 171m 77m 2960 S 1.0 7.8 3:48.15 Xorg 2907 user 20 0 98.7m 11m 9100 S 0.3 1.2 0:46.51 vmware-user-lo . . .
Example: Multiple processes in a single group
As stated previously, the CPU rate limit applies to the aggregate of all processes in the resource group. This concept is shown in the following example.
The factorial calculation is performed simultaneously in two separate psql sessions, each of which was added to resource group resgrp_b that has cpu_rate_limit set to .4 (CPU usage of 40%).
Session 1
edb=# SET edb_resource_group TO resgrp_b; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- resgrp_b (1 row) edb=# SELECT 20000!;
Session 2
edb=# SET edb_resource_group TO resgrp_b; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- resgrp_b (1 row) edb=# SELECT 20000!;
A third session monitors the CPU usage:
$ top top - 16:53:03 up 4:31, 7 users, load average: 0.31, 0.19, 0.27 Tasks: 202 total, 1 running, 201 sleeping, 0 stopped, 0 zombie Cpu(s): 41.2%us, 3.0%sy, 0.0%ni, 55.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0 Mem: 1025624k total, 792020k used, 233604k free, 23844k buffers Swap: 103420k total, 13404k used, 90016k free, 373508k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 29857 enterpri 20 0 195m 4708 3312 S 19.9 0.5 0:57.35 edb-postgres 28915 enterpri 20 0 195m 5900 4212 S 19.6 0.6 5:35.49 edb-postgres 3040 user 20 0 278m 22m 14m S 1.0 2.2 3:54.99 knotify4 1033 root 20 0 171m 78m 2960 S 0.3 7.8 3:55.71 Xorg . . .
Two new processes named edb-postgres have %CPU values of 19.9 and 19.6. The sum is close to the 40% CPU usage set for resource group resgrp_b.
This command sequence displays the sum of all edb-postgres processes sampled over half-second time intervals. This example shows how the total CPU usage of the processes in the resource group changes over time as EDB Resource Manager throttles the processes to keep the total resource group CPU usage near 40%.
$ while [[ 1 -eq 1 ]]; do top -d0.5 -b -n2 | grep edb-postgres | awk '{ SUM += $9} END { print SUM / 2 }'; done 37.2 39.1 38.9 38.3 44.7 39.2 42.5 39.1 39.2 39.2 41 42.85 46.1 . . .
Example: Multiple processes in multiple groups
In this example, two additional psql sessions are used along with the previous two sessions. The third and fourth sessions perform the same factorial calculation in resource group resgrp_c with a cpu_rate_limit of .3 (30% CPU usage).
Session 3
edb=# SET edb_resource_group TO resgrp_c; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- resgrp_c (1 row) edb=# SELECT 20000!;
Session 4
edb=# SET edb_resource_group TO resgrp_c; SET edb=# SHOW edb_resource_group;
edb_resource_group -------------------- resgrp_c (1 row) edb=# SELECT 20000!;
The top command displays the following output:
$ top top - 17:45:09 up 5:23, 8 users, load average: 0.47, 0.17, 0.26 Tasks: 203 total, 4 running, 199 sleeping, 0 stopped, 0 zombie Cpu(s): 70.2%us, 0.0%sy, 0.0%ni, 29.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0 Mem: 1025624k total, 806140k used, 219484k free, 25296k buffers Swap: 103420k total, 13404k used, 90016k free, 374092k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 29857 enterpri 20 0 195m 4820 3324 S 19.9 0.5 4:25.02 edb-postgres 28915 enterpri 20 0 195m 5900 4212 R 19.6 0.6 9:07.50 edb-postgres 29023 enterpri 20 0 195m 4744 3248 R 16.3 0.5 4:01.73 edb-postgres 11019 enterpri 20 0 195m 4120 2764 R 15.3 0.4 0:04.92 edb-postgres 2907 user 20 0 98.7m 12m 9112 S 1.3 1.2 0:56.54 vmware-user-lo 3040 user 20 0 278m 22m 14m S 1.3 2.2 4:38.73 knotify4
The two resource groups in use have CPU usage limits of 40% and 30%. The sum of the %CPU column for the first two edb-postgres processes is 39.5 (approximately 40%, which is the limit for resgrp_b). The sum of the %CPU column for the third and fourth edb-postgres processes is 31.6 (approximately 30%, which is the limit for resgrp_c).
The sum of the CPU usage limits of the two resource groups to which these processes belong is 70%. The following output shows that the sum of the four processes borders around 70%:
$ while [[ 1 -eq 1 ]]; do top -d0.5 -b -n2 | grep edb-postgres | awk '{ SUM += $9} END { print SUM / 2 }'; done 61.8 76.4 72.6 69.55 64.55 79.95 68.55 71.25 74.85 62 74.85 76.9 72.4 65.9 74.9 68.25
By contrast, if three sessions are processing. where two sessions remain in resgrp_b but the third session doesn't belong to any resource group, the top command shows the following output:
$ top top - 17:24:55 up 5:03, 7 users, load average: 1.00, 0.41, 0.38 Tasks: 199 total, 3 running, 196 sleeping, 0 stopped, 0 zombie Cpu(s): 99.7%us, 0.3%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0 Mem: 1025624k total, 797692k used, 227932k free, 24724k buffers Swap: 103420k total, 13404k used, 90016k free, 374068k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 29023 enterpri 20 0 195m 4744 3248 R 58.6 0.5 2:53.75 edb-postgres 28915 enterpri 20 0 195m 5900 4212 S 18.9 0.6 7:58.45 edb-postgres 29857 enterpri 20 0 195m 4820 3324 S 18.9 0.5 3:14.85 edb-postgres 1033 root 20 0 174m 81m 2960 S 1.7 8.2 4:26.50 Xorg 3040 user 20 0 278m 22m 14m S 1.0 2.2 4:21.20 knotify4
The second and third edb-postgres processes belonging to the resource group where the CPU usage is limited to 40% have a total CPU usage of 37.8. However, the first edb-postgres process has a 58.6% CPU usage, as it isn't within a resource group. It basically uses the remaining available CPU resources on the system.
Likewise, the following output shows the sum of all three sessions is around 95%, since one of the sessions has no set limit on its CPU usage:
$ while [[ 1 -eq 1 ]]; do top -d0.5 -b -n2 | grep edb-postgres | awk '{ SUM += $9} END { print SUM / 2 }'; done 96 90.35 92.55 96.4 94.1 90.7 95.7 95.45 93.65 87.95 96.75 94.25 95.45 97.35 92.9 96.05 96.25 94.95 . . .