EDB Resource Manager v14

EDB Resource Manager is an EDB Postgres Advanced Server feature that provides the capability to control the usage of operating system resources used by EDB Postgres Advanced Server processes.

This capability allows you to protect the system from processes that may 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, available to all databases in an EDB Postgres Advanced Server instance, on which various resource usage limits can be defined. EDB Postgres Advanced Server processes that are assigned as members of a given resource group are then controlled by EDB Resource Manager so that the aggregate resource usage of all processes in the group is kept near the limits defined on the group.
  • Data definition language commands are used to create, alter, and drop resource groups. These commands can only be used by a database user with superuser privileges.
  • The desired, aggregate consumption level of all processes belonging to a resource group is defined by resource type parameters. There are different resource type parameters for the different types of system resources currently supported by EDB Resource Manager.
  • Multiple resource groups can be created, each with different settings for its resource type parameters, thus defining 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 there are multiple resource type parameters with defined settings in a resource group, the actual resource consumption may be significantly lower for certain resource types than their defined resource type parameter settings. This is because EDB Resource Manager throttles processes attempting to keep all resources with defined resource type settings within their defined limits.
  • The definition of available resource groups and their resource type settings are stored in a shared global system catalog. Thus, resource groups can be utilized by all databases in a given EDB Postgres Advanced Server instance.
  • The edb_max_resource_groups configuration parameter sets the maximum number of resource groups that can be active simultaneously with running processes. The default setting is 16 resource groups. Changes to this parameter take effect on database server restart.
  • 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.
  • A default resource group can be assigned to a role using the ALTER ROLE ... SET command, or to a database by the ALTER DATABASE ... SET command. The entire database server instance can be assigned a default resource group by setting the parameter in the postgresql.conf file.
  • In order 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

The data definition language commands described in this section provide for the creation and management of 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. Resource limits can then be defined 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

The following example results in the creation of 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

The following 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.

The first form renames the resource group:

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

The second form assigns a resource type to the resource group:

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

The third form resets the assignment of a resource type to its default within 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 first form with the RENAME TO clause assigns a new name to an existing resource group.

The second form with the SET resource_type TO clause either assigns the specified literal value to a resource type, or resets the resource type when DEFAULT is specified. Resetting or setting a resource type to DEFAULT means that the resource group has no defined limit on that resource type.

The third form with the RESET resource_type clause resets the resource type for the group as described previously.

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

Parameters

group_name

The name of the resource group to be altered.

new_name

The new name to be assigned to the resource group.

resource_type

The resource type parameter specifying the type of resource to which a usage value is to be set.

value | DEFAULT

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

Example

The following are examples 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

The following 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 be removed.

IF EXISTS

Don't throw an error if the resource group does not exist. A notice is issued in this case.

Example

The following example removes 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 as shown by the following.

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

Processes can be included by default in a resource group by assigning a default resource group to roles, databases, or an entire database server instance.

A default resource group can be assigned to a role using the ALTER ROLE ... SET command. For more information about the ALTER ROLE command, refer to the PostgreSQL core documentation available at:

https://www.postgresql.org/docs/current/static/sql-alterrole.html

A default resource group can be assigned to a database by the ALTER DATABASE ... SET command. For more information about the ALTER DATABASE command, refer to the PostgreSQL core documentation available at:

https://www.postgresql.org/docs/current/static/sql-alterdatabase.html

The entire database server instance can be assigned a default resource group by setting the edb_resource_group configuration parameter in the postgresql.conf file as shown by the following.

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

A change to edb_resource_group in the postgresql.conf file requires a configuration file reload before it takes 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 as shown by the following.

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

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

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

For removing 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 and reload the configuration file.

Monitoring processes in resource groups

After resource groups have been created, the number of processes actively using these resource groups can be obtained from the view edb_all_resource_groups.

The columns in edb_all_resource_groups are the following:

  • 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 applicable 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 applicable 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, but indicate how EDB Resource Manager sets the resource limit for an individual process based upon the number of active processes in the resource group.

The following 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 as follows.

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, note that 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

CPU usage of a resource group is controlled 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 should not exceed. Thus, the value assigned to cpu_rate_limit should typically be 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 has been set for the resource group.

When multiplied by 100, the cpu_rate_limit can also be interpreted as the CPU usage percentage for a resource group.

EDB Resource Manager utilizes 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 may be interrupted and put into sleep mode for a short interval of 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

The ALTER RESOURCE GROUP command with the SET cpu_rate_limit clause is used to set the CPU rate limit for a resource group.

In the following 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%, etc.

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

The following 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 not only affects new processes that are assigned to the group, but any currently running processes that are members of the group are immediately affected by the change. That is, if the cpu_rate_limit is changed from .5 to .3, currently running processes in the group would be throttled downward so that the aggregate group CPU usage would be near 30% instead of 50%.

To illustrate the effect of setting the CPU rate limit for resource groups, the following examples use a CPU-intensive calculation of 20000 factorial (multiplication of 20000 * 19999 * 19998, etc.) performed by the query SELECT 20000!; run in the psql command line utility.

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

The following shows that the current process is set to use resource group resgrp_b. The factorial calculation is then started.

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 psql session performing the factorial calculation is shown by the row where edb-postgres appears under the COMMAND column. The CPU usage of the session shown under the %CPU column shows 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 illustrated in the following example.

The factorial calculation is performed simultaneously in two separate psql sessions, each of which has been 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
    .
    .
    .

There are now two processes named edb-postgres with %CPU values of 19.9 and 19.6, whose sum is close to the 40% CPU usage set for resource group resgrp_b.

The following command sequence displays the sum of all edb-postgres processes sampled over half second time intervals. This 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 within 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) and 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 does not 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 is not within a resource group, and basically utilizes 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

Writing to shared buffers is controlled by setting 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 should write to or “dirty” the shared buffers. An example setting would be 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 has been set for the resource group.

EDB Resource Manager utilizes 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 may be interrupted and put into sleep mode for a short interval of 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

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

In the following 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, etc.

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

The following 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 not only affects new processes that are assigned to the group, but any currently running processes that are members of the group are immediately affected by the change. That is, if the dirty_rate_limit is changed from 12288 to 3072, currently running processes in the group would be throttled downward so that the aggregate group dirty rate would be near 3072 kilobytes per second instead of 12288 kilobytes per second.

To illustrate the effect of setting the dirty rate limit for resource groups, the following 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. This results in 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 provides the information 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.

In order to use the pg_stat_statements module, perform the following steps.

Step 1: In the postgresql.conf file, add $libdir/pg_stat_statements to the shared_preload_libraries configuration parameter as shown by the following.

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

Step 2: Restart the database server.

Step 3: Use the CREATE EXTENSION command to complete the creation of the pg_stat_statements module.

edb=# CREATE EXTENSION pg_stat_statements SCHEMA public;
CREATE EXTENSION

The pg_stat_statements_reset() function is used to clear 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

The following sequence of commands shows the creation of 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.

Finally, the INSERT command 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.

Note that 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 the steps are repeated again 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 usage 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

First, note the total time was only 2432.165 milliseconds as compared to 13496.184 milliseconds when a resource group with a dirty rate limit set to 6144 kilobytes per second was used.

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.

Note that the actual dirty rate of 33692 kilobytes per second is significantly 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 has been 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 were started after the SELECT pg_stat_statements_reset() command in session 2 was run.

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

First, note 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. This is shown in the following calculations.

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 illustrated 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 were started after the SELECT pg_stat_statements_reset() command in session 4 was run.

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

First note that 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, as compared to 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).

Thus, this demonstrates 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

This section describes the system catalogs that 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.