pgnodemx

Overview

SQL functions that allow capture of node OS metrics from PostgreSQL

Security

Executing role must have been granted pg_monitor membership (pgmonitor for PostgreSQL version 9.6 and below - see Compatibility section below).

cgroup Related Functions

For detailed information about the various virtual files available on the cgroup file system, see:

• cgroup v1: https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/index.html
• cgroup v2: https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html

General Access Functions

cgroup virtual files fall into (at least) the following general categories, each with a generic SQL access function:

• BIGINT single line scalar values - SELECT cgroup_scalar_bigint(filename);

  • cgroup v1 examples: blkio.leaf_weight, blkio.weight, cpuacct.usage, cpuacct.usage_percpu, cpuacct.usage_percpu_sys, cpuacct.usage_percpu_user, cpuacct.usage_sys, cpuacct.usage_user, cpu.cfs_period_us, cpu.cfs_quota_us, cpu.rt_period_us, cpu.rt_runtime_us, cpu.shares, cpuacct.usage, memory.failcnt, memory.kmem.failcnt, memory.kmem.limit_in_bytes, memory.kmem.max_usage_in_bytes, memory.kmem.tcp.failcnt, memory.kmem.tcp.limit_in_bytes, memory.kmem.tcp.max_usage_in_bytes, memory.kmem.tcp.usage_in_bytes, memory.kmem.usage_in_bytes, memory.limit_in_bytes, memory.max_usage_in_bytes, memory.memsw.failcnt, memory.memsw.limit_in_bytes, memory.memsw.max_usage_in_bytes, memory.memsw.usage_in_bytes, memory.move_charge_at_immigrate, memory.soft_limit_in_bytes, memory.usage_in_bytes, net_cls.classid, net_prio.prioidx
  • cgroup v2 examples: cgroup.freeze, cgroup.max.depth, cgroup.max.descendants, cpu.weight, cpu.weight.nice, memory.current, memory.high, memory.low, memory.max, memory.min, memory.oom.group, memory.swap.current, memory.swap.max, pids.current, pids.max

• FLOAT8 single line scalar values - SELECT cgroup_scalar_float8(filename);

  • cgroup v1 examples: (none known)
  • cgroup v2 examples: cpu.uclamp.max, cpu.uclamp.min

• TEXT single line scalar values - SELECT cgroup_scalar_text(filename);

  • cgroup v1 examples: (none known)
  • cgroup v2 examples: cgroup.type

• SETOF(BIGINT) multiline scalar values - SELECT * FROM cgroup_setof_bigint(filename);

  • cgroup v1 examples: cgroup.procs
  • cgroup v2 examples: cgroup.procs, cgroup.threads

• SETOF(TEXT) multiline scalar values - SELECT * FROM cgroup_setof_text(filename);

  • cgroup v1 examples: (none known)
  • cgroup v2 examples: (none known)

• ARRAY[BIGINT] space separated values - SELECT cgroup_array_bigint(filename);

  • cgroup v1 examples: (none known)
  • cgroup v2 examples: cpu.max

• ARRAY[TEXT] space separated values - SELECT cgroup_array_text(filename)

  • cgroup v1 examples: cpuacct.usage_all (sort of)
  • cgroup v2 examples: cgroup.controllers, cgroup.subtree_control

• SETOF(TEXT, BIGINT) flat keyed - SELECT * FROM cgroup_setof_kv(filename);

  • cgroup v1 examples: cpuacct.stat, cpu.stat, cpuacct.stat, memory.oom_control, memory.stat, net_prio.ifpriomap, blkio.io_merged, blkio.io_merged_recursive, blkio.io_queued, blkio.io_queued_recursive, blkio.io_service_bytes, blkio.io_service_bytes_recursive, blkio.io_serviced, blkio.io_serviced_recursive, blkio.io_service_time, blkio.io_service_time_recursive, blkio.io_wait_time, blkio.io_wait_time_recursive
  • cgroup v2 examples: cgroup.events, cgroup.stat, cpu.stat, io.pressure, io.weight, memory.events, memory.events.local, memory.stat, memory.swap.events, pids.events

• SETOF(TEXT, TEXT, BIGINT) key/subkey/value space separated - SELECT * FROM cgroup_setof_ksv(filename);

  • cgroup v1 examples: blkio.throttle.io_service_bytes, blkio.throttle.io_serviced
  • cgroup v2 examples: (none known)

• SETOF(TEXT, TEXT, FLOAT8) nested keyed - SELECT * FROM cgroup_setof_nkv(filename);

  • cgroup v1 examples: (none known)
  • cgroup v2 examples: memory.pressure, cpu.pressure, io.max, io.stat

In each case, the filename must be in the form <controller>.<metric>, e.g. memory.stat.

Get status of cgroup support

SELECT current_setting('pgnodemx.cgroup_enabled');

• Returns boolean result ("on"/"off").
• This value may be explicitly set in postgresql.conf
• However the extension will disable it at runtime if the location pointed to by pgnodemx.cgrouproot does not exist or is not a valid cgroup v1 or v2 mount.

Get current cgroup mode

SELECT cgroup_mode();

• Returns the current cgroup mode. Possible values are "legacy", "unified", "hybrid", and "disabled". These correspond to cgroup v1, cgroup v2, mixed, and disabled, respectively.
• Currently "hybrid" mode is not supported; it might be in the future.

Determine if Running Containerized

SELECT current_setting('pgnodemx.containerized');

• Returns boolean result ("on"/"off"). The extension attempts to heuristically determine whether PostgreSQL is running under a container, but this value may be explicitly set in postgresql.conf to override the heuristically determined value. The value of this setting influences the cgroup paths which are used to read the cgroup controller files.

Get cgroup Paths

SELECT controller, path FROM cgroup_path();

• Returns the path to each supported cgroup controller.

Get cgroup process count

SELECT cgroup_process_count();

• Returns the number of processes assigned to the cgroup
• For cgroup v1, based on the "memory" controller cgroup.procs file. For cgroup v2, based on the unified cgroup.procs file.

Environment Variable Related Functions

Get Environment Variable as TEXT

SELECT envvar_text('PGDATA');

• Returns the value of requested environment variable as TEXT

Get Environment Variable as BIGINT

SELECT envvar_bigint('PGPORT');

• Returns the value of requested environment variable as BIGINT

/proc Related Functions

For more detailed information about the /proc file system virtual files, please see: https://www.kernel.org/doc/html/latest/filesystems/proc.html

Get "/proc/diskstats" as a virtual table

SELECT * FROM proc_diskstats();

Get "/proc/self/mountinfo" as a virtual table

SELECT * FROM proc_mountinfo();

Get "/proc/meminfo" as a virtual table

SELECT * FROM proc_meminfo();

Get "/proc/self/net/dev" as a virtual table

SELECT * FROM proc_network_stats();

Get "/proc/\<pid>/io" for all PostgreSQL processes as a virtual table

SELECT * FROM proc_pid_io();

Get the full command line, uid, and username for all PostgreSQL processes as a virtual table

SELECT * FROM proc_pid_cmdline();

Get "/proc/\<pid>/stat" for all PostgreSQL processes as a virtual table

SELECT * FROM proc_pid_stat();

Get first line of "/proc/stat" as a virtual table

SELECT * FROM proc_cputime();

Get first line of "/proc/loadavg" as a virtual table

SELECT * FROM proc_loadavg();

pg_proctab Compatibility Functions for use with pg_top

Five functions are provided in an extension that match the SQL interface presented by the pg_proctab extension.

CREATE EXTENSION pg_proctab VERSION "0.0.10-compat";
SELECT * FROM pg_cputime();
SELECT * FROM pg_loadavg();
SELECT * FROM pg_memusage();
SELECT * FROM pg_diskusage();
SELECT * FROM pg_proctab();

These functions are not installed by default. They may be installed by installing pg_proctab VERSION "0.0.10-compat" after installing the pgnodemx extension.

System Information Related Functions

Get file system information as a virtual table

SELECT * FROM fsinfo(path text);

• Returns major_number, minor_number, type, block_size, blocks, total_bytes, free_blocks, free_bytes, available_blocks, available_bytes, total_file_nodes, free_file_nodes, and mount_flags for the file system on which path is mounted. Note: Some filesystems can return unexpected values (like MAX_UINT64) if these numbers cannot be determined.

Get current FIPS mode

SELECT fips_mode();

• Returns TRUE if openssl is currently running in FIPS mode, otherwise FALSE.

Get openssl version string

select openssl_version();

Get source C library path for a function symbol

SELECT symbol_filename(sym_name text);

• Returns the source C library from whence the C function sym_name comes. Returns NULL on any errors.

Convert number of kernel memory pages to bytes

SELECT kpages_to_bytes(num_k_pages numeric);

Kubernetes DownwardAPI Related Functions

For more detailed information about the Kubernetes DownwardAPI please see: https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/

Get status of kdapi_enabled

SELECT current_setting('pgnodemx.kdapi_enabled');

• Returns boolean result ("on"/"off").
• This value may be explicitly set in postgresql.conf
• However the extension will disable it at runtime if the location pointed to by pgnodemx.kdapi_path does not exist.

Access "key equals quoted value" files

SELECT * FROM kdapi_setof_kv('filename');

Get scalar BIGINT from file

SELECT kdapi_scalar_bigint('filename text');

General Information Functions

Get pgnodemx version information

SELECT pgnodemx_version();

• If VSTR environment variable is set at compile time, returns that value
• Otherwise returns the value of the short git hash
• If not compiling from the git repository and VSTR is unset, returns "none"

Get currently running PostgreSQL executable path

SELECT exec_path();

Get uid, username, gid, groupname, and filemode for a file

SELECT * FROM stat_file(filename);

Configuration

• Add pgnodemx to shared_preload_libraries in postgresql.conf.

  shared_preload_libraries = 'pgnodemx'

• The following custom parameters may be set. The values shown are defaults. If the default values work for you, there is no need to add these to postgresql.conf.

  # enable or disable the cgroup facility
  pgnodemx.cgroup_enabled = on
  # force use of "containerized" assumptions for cgroup file paths
  pgnodemx.containerized = off
  # specify location of cgroup mount
  pgnodemx.cgrouproot = '/sys/fs/cgroup'
  # enable cgroup functions
  pgnodemx.cgroup_enabled = on
  # enable or disable the Kubernetes DownwardAPI facility
  pgnodemx.kdapi_enabled = on
  # specify location of Kubernetes DownwardAPI files
  pgnodemx.kdapi_path = '/etc/podinfo'

  Notes:

• If pgnodemx.cgroup_enabled is defined in postgresql.conf, and set to off (or false), then all cgroup* functions will return NULL, or zero rows, except cgroup_mode() which will return "disabled".
• If pgnodemx.containerized is defined in postgresql.conf, that value will override pgnodemx heuristics. When not specified, pgnodemx heuristics will determine if the value should be on or off at runtime.
• If the location specified by pgnodemx.cgrouproot, default or as set in postgresql.conf, is not accessible (does not exist, or otherwise causes an error when accessed), then pgnodemx.cgroup_enabled is forced to off at runtime and all cgroup* functions will return NULL, or zero rows, except cgroup_mode() which will return "disabled".
• If the location specified by pgnodemx.kdapi_path, default or as set in postgresql.conf, is not accessible (does not exist, or otherwise causes an error when accessed), then pgnodemx.kdapi_enabled is forced to off at runtime and all kdapi* functions will return NULL, or zero rows.

Installation

Compatibility

• PostgreSQL version 9.5 or newer is required.
• On PostgreSQL version 9.6 or earlier, a role called pgmonitor must be created, and the user calling these functions must be granted that role.

Compile and Install

Clone PostgreSQL repository:

$> git clone https://github.com/postgres/postgres.git

Checkout REL_12_STABLE (for example) branch:

$> git checkout REL_12_STABLE

Make PostgreSQL:

$> ./configure
$> make install -s

Change to the contrib directory:

$> cd contrib

Clone pgnodemx extension:

$> git clone https://github.com/crunchydata/pgnodemx

Change to pgnodemx directory:

$> cd pgnodemx

Build pgnodemx:

$> make

Install pgnodemx:

$> make install

Using PGXS

If an instance of PostgreSQL is already installed, then PGXS can be utilized to build and install pgnodemx. Ensure that PostgreSQL binaries are available via the $PATH environment variable then use the following commands.

$> make USE_PGXS=1
$> make USE_PGXS=1 install

Configure

The following bash commands should configure your system to utilize pgnodemx. Replace all paths as appropriate. It may be prudent to visually inspect the files afterward to ensure the changes took place.

Initialize PostgreSQL (if needed):

$> initdb -D /path/to/data/directory

Create Target Database (if needed):

$> createdb <database>

Install pgnodemx functions:

Edit postgresql.conf and add pgnodemx to the shared_preload_libraries line, and change custom settings as mentioned above.

Finally, restart PostgreSQL (method may vary):

$> service postgresql restart

Install the extension into your database:

psql <database>
CREATE EXTENSION pgnodemx;

TODO

• Map more /proc files to virtual tables
• Add support for "hybrid" cgroup mode