EDB Resource Manager v14

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EDB Resource Manager is an EDB Postgres Advanced Server feature that lets you control the use of operating system resources used by EDB Postgres Advanced Server processes.

This capability allows you to protect the system from processes that might uncontrollably overuse and monopolize certain system resources.

The following are some key points about using EDB Resource Manager:

  • The basic component of EDB Resource Manager is a resource group. A resource group is a named, global group. It's available to all databases in an EDB Postgres Advanced Server instance, and you can define various resource usage limits on it. EDB Postgres Advanced Server processes that are assigned as members of a given resource group are then controlled by EDB Resource Manager. This configuration keeps the aggregate resource use of all processes in the group near the limits defined on the group.
  • Data definition language commands are used to create, alter, and drop resource groups. Only a database user with superuser privileges can use these commands.
  • Resource type parameters define the desired aggregate consumption level of all processes belonging to a resource group. You use different resource type parameters for the different types of system resources currently supported by EDB Resource Manager.
  • You can create multiple resource groups, each with different settings for its resource type parameters, which defines different consumption levels for each resource group.
  • EDB Resource Manager throttles processes in a resource group to keep resource consumption near the limits defined by the resource type parameters. If multiple resource type parameters have defined settings in a resource group, the actual resource consumption might be significantly lower for certain resource types than their defined resource type parameter settings. This lower consumption happens because EDB Resource Manager throttles processes, attempting to keep all resources with defined resource type settings within their defined limits.
  • The definitions of available resource groups and their resource type settings are stored in a shared global system catalog. Thus, all databases in a given EDB Postgres Advanced Server instance can use resource groups.
  • The edb_max_resource_groups configuration parameter sets the maximum number of resource groups that can be active at the same time as running processes. The default setting is 16 resource groups. Changes to this parameter take effect when you restart the database server.
  • Use the SET edb_resource_group TO group_name command to assign the current process to a specified resource group. Use the RESET edb_resource_group command or SET edb_resource_group to DEFAULT to remove the current process from a resource group.
  • You can assign a default resource group to a role using the ALTER ROLE ... SET command or to a database using the ALTER DATABASE ... SET command. You can assign the entire database server instance a default resource group by setting the parameter in the postgresql.conf file.
  • To include resource groups in a backup file of the database server instance, use the pg_dumpall backup utility with default settings. That is, don't specify any of the --globals-only, --roles-only, or --tablespaces-only options.

Creating and managing resource groups

Use these data definition language commands to create and manage resource groups.

CREATE RESOURCE GROUP

Use the CREATE RESOURCE GROUP command to create a new resource group.

CREATE RESOURCE GROUP <group_name>;

Description

The CREATE RESOURCE GROUP command creates a resource group with the specified name. You can then define resource limits on the group with the ALTER RESOURCE GROUP command. The resource group is accessible from all databases in the EDB Postgres Advanced Server instance.

To use the CREATE RESOURCE GROUP command, you must have superuser privileges.

Parameters

group_name

The name of the resource group.

Example

This example creates three resource groups named resgrp_a, resgrp_b, and resgrp_c:

edb=# CREATE RESOURCE GROUP resgrp_a;
CREATE RESOURCE GROUP
edb=# CREATE RESOURCE GROUP resgrp_b;
CREATE RESOURCE GROUP
edb=# CREATE RESOURCE GROUP resgrp_c;
CREATE RESOURCE GROUP

This query shows the entries for the resource groups in the edb_resource_group catalog:

edb=# SELECT * FROM edb_resource_group;
 rgrpname  | rgrpcpuratelimit | rgrpdirtyratelimit
-----------+------------------+--------------------
 resgrp_a  |                0 | 0
 resgrp_b  |                0 | 0
 resgrp_c  |                0 | 0
(3 rows)

ALTER RESOURCE GROUP

Use the ALTER RESOURCE GROUP command to change the attributes of an existing resource group. The command syntax comes in three forms.

This form renames the resource group:

ALTER RESOURCE GROUP <group_name> RENAME TO <new_name>;

This form assigns a resource type to the resource group:

ALTER RESOURCE GROUP <group_name> SET
  <resource_type> { TO | = } { <value> | DEFAULT };

This form resets the assignment of a resource type to its default in the group:

ALTER RESOURCE GROUP <group_name> RESET <resource_type>;

Description

The ALTER RESOURCE GROUP command changes certain attributes of an existing resource group.

The form with the RENAME TO clause assigns a new name to an existing resource group.

The form with the SET resource_type TO clause assigns the specified literal value to a resource type. Or, when you specify DEFAULT, it resets the resource type. Resetting a resource type means that the resource group has no defined limit on that resource type.

The form with the RESET resource_type clause resets the resource type for the group.

To use the ALTER RESOURCE GROUP command, you must have superuser privileges.

Parameters

group_name

The name of the resource group to alter.

new_name

The new name to assign to the resource group.

resource_type

Specifies the type of resource to which to set a usage value.

value | DEFAULT

When value is specified, the literal value to assign to resource_type. Specify DEFAULT to reset the assignment of resource_type for the resource group.

Example

These examples show the use of the ALTER RESOURCE GROUP command:

edb=# ALTER RESOURCE GROUP resgrp_a RENAME TO newgrp;
ALTER RESOURCE GROUP
edb=# ALTER RESOURCE GROUP resgrp_b SET cpu_rate_limit = .5;
ALTER RESOURCE GROUP
edb=# ALTER RESOURCE GROUP resgrp_b SET dirty_rate_limit = 6144;
ALTER RESOURCE GROUP
edb=# ALTER RESOURCE GROUP resgrp_c RESET cpu_rate_limit;
ALTER RESOURCE GROUP

This query shows the results of the ALTER RESOURCE GROUP commands to the entries in the edb_resource_group catalog:

edb=# SELECT * FROM edb_resource_group;
 rgrpname  | rgrpcpuratelimit | rgrpdirtyratelimit
-----------+------------------+--------------------
 newgrp    | 0                | 0
 resgrp_b  | 0.5              | 6144
 resgrp_c  | 0                | 0
(3 rows)

DROP RESOURCE GROUP

Use the DROP RESOURCE GROUP command to remove a resource group.

DROP RESOURCE GROUP [ IF EXISTS ] <group_name>;

Description

The DROP RESOURCE GROUP command removes a resource group with the specified name.

To use the DROP RESOURCE GROUP command, you must have superuser privileges.

Parameters

group_name

The name of the resource group to remove.

IF EXISTS

Don't throw an error if the resource group doesn't exist. Instead, issue a notice.

Example

This example removes the resource group newgrp:

edb=# DROP RESOURCE GROUP newgrp;
DROP RESOURCE GROUP

Assigning a process to a resource group

Use the SET edb_resource_group TO group_name command to assign the current process to a specified resource group:

edb=# SET edb_resource_group TO resgrp_b;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
 resgrp_b
(1 row)

The resource type settings of the group take effect on the current process immediately. If you use the command to change the resource group assigned to the current process, the resource type settings of the newly assigned group take effect immediately.

You can include processes in a resource group by default by assigning a default resource group to roles, databases, or an entire database server instance.

You can assign a default resource group to a role using the ALTER ROLE ... SET command. For more information about the ALTER ROLE command, see the PostgreSQL core documentation.

You can assign a default resource group to a database by using the ALTER DATABASE ... SET command. For more information about the ALTER DATABASE command, see the PostgreSQL core documentation.

You can assign the entire database server instance a default resource group by setting the edb_resource_group configuration parameter in the postgresql.conf file:

# - EDB Resource Manager -
#edb_max_resource_groups = 16           # 0-65536 (change requires restart)
edb_resource_group = 'resgrp_b'

If you change edb_resource_group in the postgresql.conf file, reload the configuration file to make it take effect on the database server instance.

Removing a process from a resource group

Set edb_resource_group to DEFAULT or use RESET edb_resource_group to remove the current process from a resource group:

edb=# SET edb_resource_group TO DEFAULT;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
(1 row)

To remove a default resource group from a role, use the ALTER ROLE ... RESET form of the ALTER ROLE command.

To remove a default resource group from a database, use the ALTER DATABASE ... RESET form of the ALTER DATABASE command.

To remove a default resource group from the database server instance, set the edb_resource_group configuration parameter to an empty string in the postgresql.conf file. Then, reload the configuration file.

Monitoring processes in resource groups

After you create resource groups, you can get the number of processes actively using these resource groups from the view edb_all_resource_groups.

The following are the columns in edb_all_resource_groups:

  • group_name. Name of the resource group.
  • active_processes. Number of active processes in the resource group.
  • cpu_rate_limit. The value of the CPU rate limit resource type assigned to the resource group.
  • per_process_cpu_rate_limit. The CPU rate limit that applies to an individual active process in the resource group.
  • dirty_rate_limit. The value of the dirty rate limit resource type assigned to the resource group.
  • per_process_dirty_rate_limit. The dirty rate limit that applies to an individual active process in the resource group.
Note

Columns per_process_cpu_rate_limit and per_process_dirty_rate_limit don't show the actual resource consumption used by the processes. They indicate how EDB Resource Manager sets the resource limit for an individual process based on the number of active processes in the resource group.

This example shows edb_all_resource_groups when resource group resgrp_a contains no active processes, resource group resgrp_b contains two active processes, and resource group resgrp_c contains one active process:

edb=# SELECT * FROM edb_all_resource_groups ORDER BY group_name;
-[ RECORD 1 ]-----------------+------------------
 group_name                   | resgrp_a
 active_processes             | 0
 cpu_rate_limit               | 0.5
 per_process_cpu_rate_limit   |
 dirty_rate_limit             | 12288
 per_process_dirty_rate_limit |
-[ RECORD 2 ]-----------------+------------------
 group_name                   | resgrp_b
 active_processes             | 2
 cpu_rate_limit               | 0.4
 per_process_cpu_rate_limit   | 0.195694289022895
 dirty_rate_limit             | 6144
 per_process_dirty_rate_limit | 3785.92924684337
-[ RECORD 3 ]-----------------+------------------
 group_name                   | resgrp_c
 active_processes             | 1
 cpu_rate_limit               | 0.3
 per_process_cpu_rate_limit   | 0.292342129631091
 dirty_rate_limit             | 3072
 per_process_dirty_rate_limit | 3072

The CPU rate limit and dirty rate limit settings that are assigned to these resource groups are:

edb=# SELECT * FROM edb_resource_group;
 rgrpname  | rgrpcpuratelimit | rgrpdirtyratelimit
-----------+------------------+--------------------
 resgrp_a  | 0.5              | 12288
 resgrp_b  | 0.4              | 6144
 resgrp_c  | 0.3              | 3072
(3 rows)

In the edb_all_resource_groups view, the per_process_cpu_rate_limit and per_process_dirty_rate_limit values are roughly the corresponding CPU rate limit and dirty rate limit divided by the number of active processes.

CPU usage throttling

Control CPU use of a resource group by setting the cpu_rate_limit resource type parameter.

Set the cpu_rate_limit parameter 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 to cpu_rate_limit is typically less than or equal to 1.

On multicore systems, you can apply the cpu_rate_limit to more than one CPU core by setting it to greater than 1. For example, if cpu_rate_limit is set to 2.0, you use 100% of two CPUs.

The valid range of the cpu_rate_limit parameter 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_limit as the CPU usage percentage for a resource group.

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.

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 as shown under the %CPU column. The following is a snapshot at an arbitrary point in time, as the top command output periodically changes:

$ 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
    .
    .
    .

Dirty buffer throttling

To control writing to shared buffers, set the dirty_rate_limit resource type parameter.

Set the dirty_rate_limit parameter to the number of kilobytes per second for the combined rate at which all the processes in the group write to, or “dirty”, the shared buffers. An example setting is 3072 kilobytes per seconds.

The valid range of the dirty_rate_limit parameter is 0 to 1.67772e+07. A setting of 0 means no dirty rate limit was set for the resource group.

EDB Resource Manager uses dirty buffer throttling to keep the aggregate shared buffer writing rate of all processes in the group near the limit specified by the dirty_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.

Setting the dirty rate limit for a resource group

Use the ALTER RESOURCE GROUP command with the SET dirty_rate_limit clause to set the dirty rate limit for a resource group.

In this example, the dirty rate limit is set to 12288 kilobytes per second for resgrp_a, 6144 kilobytes per second for resgrp_b, and 3072 kilobytes per second for resgrp_c. This means that the combined writing rate to the shared buffer of all processes assigned to resgrp_a is maintained at approximately 12288 kilobytes per second. Similarly, for all processes in resgrp_b, the combined writing rate to the shared buffer is kept to approximately 6144 kilobytes per second, and so on.

edb=# ALTER RESOURCE GROUP resgrp_a SET dirty_rate_limit TO 12288;
ALTER RESOURCE GROUP
edb=# ALTER RESOURCE GROUP resgrp_b SET dirty_rate_limit TO 6144;
ALTER RESOURCE GROUP
edb=# ALTER RESOURCE GROUP resgrp_c SET dirty_rate_limit TO 3072;
ALTER RESOURCE GROUP

This query shows the settings of dirty_rate_limit in the catalog;

edb=# SELECT rgrpname, rgrpdirtyratelimit FROM edb_resource_group;
 rgrpname  | rgrpdirtyratelimit
-----------+--------------------
 resgrp_a  |         12288
 resgrp_b  |         6144
 resgrp_c  |         3072
(3 rows)

Changing the dirty_rate_limit of a resource group affects new processes that are assigned to the group. Any currently running processes that are members of the group are also immediately affected by the change. That is, if the dirty_rate_limit is changed from 12288 to 3072, currently running processes in the group are throttled downward so that the aggregate group dirty rate is near 3072 kilobytes per second instead of 12288 kilobytes per second.

To show the effect of setting the dirty rate limit for resource groups, the examples use the following table for intensive I/O operations:

CREATE TABLE t1 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);

The FILLFACTOR = 10 clause results in INSERT commands packing rows up to only 10% per page. The result is a larger sampling of dirty shared blocks for the purpose of these examples.

The pg_stat_statements module is used to display the number of shared buffer blocks that are dirtied by a SQL command and the amount of time the command took to execute. This information is used to calculate the actual kilobytes per second writing rate for the SQL command and thus compare it to the dirty rate limit set for a resource group.

To use the pg_stat_statements module:

  1. In the postgresql.conf file, add $libdir/pg_stat_statements to the shared_preload_libraries configuration parameter:

    shared_preload_libraries = '$libdir/dbms_pipe,$libdir/edb_gen,$libdir/pg_stat_statements'

  2. Restart the database server.

  3. Use the CREATE EXTENSION command to finish creating the pg_stat_statements module:

    edb=# CREATE EXTENSION pg_stat_statements SCHEMA public;
CREATE EXTENSION

    The pg_stat_statements_reset() function clears out the pg_stat_statements view for clarity of each example.

The resource groups with the dirty rate limit settings shown in the previous query are used in these examples.

Example: Single process in a single group

This sequence of commands creates table t1. The current process is set to use resource group resgrp_b. The pg_stat_statements view is cleared out by running the pg_stat_statements_reset() function.

The INSERT command then generates a series of integers from 1 to 10,000 to populate the table and dirty approximately 10,000 blocks:

edb=# CREATE TABLE t1 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SET edb_resource_group TO resgrp_b;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
 resgrp_b
(1 row)

edb=# SELECT pg_stat_statements_reset();
 pg_stat_statements_reset
--------------------------

(1 row)

edb=# INSERT INTO t1 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000

The following shows the results from the INSERT command:

edb=# SELECT query, rows, total_time, shared_blks_dirtied FROM
pg_stat_statements;
-[ RECORD 1 ]--------+--------------------------------------------------
 query               | INSERT INTO t1 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 13496.184
 shared_blks_dirtied | 10003

The actual dirty rate is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 13496.184 ms, which yields 0.74117247 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 741.17247 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 6072 kilobytes per second.

The actual dirty rate of 6072 kilobytes per second is close to the dirty rate limit for the resource group, which is 6144 kilobytes per second.

By contrast, if you repeat the steps without the process belonging to any resource group, the dirty buffer rate is much higher:

edb=# CREATE TABLE t1 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------

(1 row)

edb=# SELECT pg_stat_statements_reset();
 pg_stat_statements_reset
--------------------------

(1 row)

edb=# INSERT INTO t1 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000

The following shows the results from the INSERT command without the use of a resource group:

edb=# SELECT query, rows, total_time, shared_blks_dirtied FROM
pg_stat_statements;
-[ RECORD 1 ]--------+--------------------------------------------------
 query               | INSERT INTO t1 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 2432.165
 shared_blks_dirtied | 10003

The total time was only 2432.165 milliseconds, compared to 13496.184 milliseconds when using a resource group with a dirty rate limit set to 6144 kilobytes per second.

The actual dirty rate without the use of a resource group is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 2432.165 ms, which yields 4.112797 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 4112.797 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 33692 kilobytes per second.

The actual dirty rate of 33692 kilobytes per second is much higher than when the resource group with a dirty rate limit of 6144 kilobytes per second was used.

Example: Multiple processes in a single group

As stated previously, the dirty rate limit applies to the aggregate of all processes in the resource group. This concept is illustrated in the following example.

For this example. the inserts are performed simultaneously on two different tables in two separate psql sessions, each of which was added to resource group resgrp_b that has a dirty_rate_limit set to 6144 kilobytes per second.

Session 1

edb=# CREATE TABLE t1 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SET edb_resource_group TO resgrp_b;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
 resgrp_b
(1 row)

edb=# INSERT INTO t1 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000

Session 2

edb=# CREATE TABLE t2 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SET edb_resource_group TO resgrp_b;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
 resgrp_b
(1 row)

edb=# SELECT pg_stat_statements_reset();
 pg_stat_statements_reset
--------------------------
(1 row)

edb=# INSERT INTO t2 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000
Note

The INSERT commands in session 1 and session 2 started after the SELECT pg_stat_statements_reset() command in session 2 ran.

The following shows the results from the INSERT commands in the two sessions. RECORD 3 shows the results from session 1. RECORD 2 shows the results from session 2.

edb=# SELECT query, rows, total_time, shared_blks_dirtied FROM
pg_stat_statements;
-[ RECORD 1 ]--------+--------------------------------------------------
 query               | SELECT pg_stat_statements_reset();
 rows                | 1
 total_time          | 0.43
 shared_blks_dirtied | 0
-[ RECORD 2 ]--------+--------------------------------------------------
 query               | INSERT INTO t2 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 30591.551
 shared_blks_dirtied | 10003
-[ RECORD 3 ]--------+--------------------------------------------------
 query               | INSERT INTO t1 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 33215.334
 shared_blks_dirtied | 10003

The total time was 33215.334 milliseconds for session 1 and 30591.551 milliseconds for session 2. When only one session was active in the same resource group, as shown in the first example, the time was 13496.184 milliseconds. Thus, more active processes in the resource group result in a slower dirty rate for each active process in the group. The following calculations show this.

The actual dirty rate for session 1 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 33215.334 ms, which yields 0.30115609 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 301.15609 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 2467 kilobytes per second.

The actual dirty rate for session 2 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 30591.551 ms, which yields 0.32698571 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 326.98571 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 2679 kilobytes per second.

The combined dirty rate from session 1 (2467 kilobytes per second) and from session 2 (2679 kilobytes per second) yields 5146 kilobytes per second, which is below the set dirty rate limit of the resource group (6144 kilobytes per seconds).

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 INSERT command in resource group resgrp_c with a dirty_rate_limit of 3072 kilobytes per second.

Sessions 1 and 2 are repeated as shown in the prior example using resource group resgrp_b with a dirty_rate_limit of 6144 kilobytes per second.

Session 3

edb=# CREATE TABLE t3 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SET edb_resource_group TO resgrp_c;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------


resgrp_c
(1 row)

edb=# INSERT INTO t3 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000

Session 4

edb=# CREATE TABLE t4 (c1 INTEGER, c2 CHARACTER(500)) WITH (FILLFACTOR = 10);
CREATE TABLE
edb=# SET edb_resource_group TO resgrp_c;
SET
edb=# SHOW edb_resource_group;
 edb_resource_group
--------------------
 resgrp_c
(1 row)

edb=# SELECT pg_stat_statements_reset();
 pg_stat_statements_reset
--------------------------

(1 row)

edb=# INSERT INTO t4 VALUES (generate_series (1,10000), 'aaa');
INSERT 0 10000
Note

The INSERT commands in all four sessions started after the SELECT pg_stat_statements_reset() command in session 4 ran.

The following shows the results from the INSERT commands in the four sessions:

  • RECORD 3 shows the results from session 1. RECORD 2 shows the results from session 2.

  • RECORD 4 shows the results from session 3. RECORD 5 shows the results from session 4.

edb=# SELECT query, rows, total_time, shared_blks_dirtied FROM
pg_stat_statements;
-[ RECORD 1 ]--------+--------------------------------------------------
 query               | SELECT pg_stat_statements_reset();
 rows                | 1
 total_time          | 0.467
 shared_blks_dirtied | 0
-[ RECORD 2 ]--------+--------------------------------------------------
 query               | INSERT INTO t2 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 31343.458
 shared_blks_dirtied | 10003
-[ RECORD 3 ]--------+--------------------------------------------------
 query               | INSERT INTO t1 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 28407.435
 shared_blks_dirtied | 10003
-[ RECORD 4 ]--------+--------------------------------------------------
 query               | INSERT INTO t3 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 52727.846
 shared_blks_dirtied | 10003
-[ RECORD 5 ]--------+--------------------------------------------------
 query               | INSERT INTO t4 VALUES (generate_series (?,?), ?);
 rows                | 10000
 total_time          | 56063.697
 shared_blks_dirtied | 10003

The times of session 1 (28407.435) and session 2 (31343.458) are close to each other, as they are both in the same resource group with dirty_rate_limit set to 6144. These times differe from the times of session 3 (52727.846) and session 4 (56063.697), which are in the resource group with dirty_rate_limit set to 3072. The latter group has a slower dirty rate limit, so the expected processing time is longer, as is the case for sessions 3 and 4.

The actual dirty rate for session 1 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 28407.435 ms, which yields 0.35212612 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 352.12612 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 2885 kilobytes per second.

The actual dirty rate for session 2 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 31343.458 ms, which yields 0.31914156 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 319.14156 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 2614 kilobytes per second.

The combined dirty rate from session 1 (2885 kilobytes per second) and from session 2 (2614 kilobytes per second) yields 5499 kilobytes per second, which is near the set dirty rate limit of the resource group (6144 kilobytes per seconds).

The actual dirty rate for session 3 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 52727.846 ms, which yields 0.18971001 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 189.71001 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 1554 kilobytes per second.

The actual dirty rate for session 4 is calculated as follows:

  • The number of blocks dirtied per millisecond (ms) is 10003 blocks / 56063.697 ms, which yields 0.17842205 blocks per millisecond.
  • Multiply the result by 1000 to give the number of shared blocks dirtied per second (1 second = 1000 ms), which yields 178.42205 blocks per second.
  • Multiply the result by 8.192 to give the number of kilobytes dirtied per second (1 block = 8.192 kilobytes), which yields approximately 1462 kilobytes per second.

The combined dirty rate from session 3 (1554 kilobytes per second) and from session 4 (1462 kilobytes per second) yields 3016 kilobytes per second, which is near the set dirty rate limit of the resource group (3072 kilobytes per seconds).

This example shows how EDB Resource Manager keeps the aggregate dirty rate of the active processes in its groups close to the dirty rate limit set for each group.

System catalogs

System catalogs store the resource group information used by EDB Resource Manager.

edb_all_resource_groups

The following table lists the information available in the edb_all_resource_groups catalog.

ColumnTypeDescription
group_namenameThe name of the resource group.
active_processesintegerNumber of currently active processes in the resource group.
cpu_rate_limitfloat8Maximum CPU rate limit for the resource group. 0 means no limit.
per_process_cpu_rate_limitfloat8Maximum CPU rate limit per currently active process in the resource group.
dirty_rate_limitfloat8Maximum dirty rate limit for a resource group. 0 means no limit.
per_process_dirty_rate_limitfloat8Maximum dirty rate limit per currently active process in the resource group.

edb_resource_group

The following table lists the information available in the edb_resource_group catalog.

ColumnTypeDescription
rgrpnamenameThe name of the resource group.
rgrpcpuratelimitfloat8Maximum CPU rate limit for a resource group. 0 means no limit.
rgrpdirtyratelimitfloat8Maximum dirty rate limit for a resource group. 0 means no limit.
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