Merge branch '6010-check-pqsql' into 'master'

wip doc for check psqlserver

See merge request !117

docs/20_Checks/check_psqlserver.md

+# check PostgreSql server
+
+## Introduction
+
+**check_psqlserver** is a plugin execute different checks on a postgreSql server instance.
+The kind of check is defined by a paameter `-m METHOD`.
+
+## Requirements
+
+The icinga user needs to connect to the database server.
+
+## Syntax
+
+`$ check_psqlserver [-i|-u|-m METHOD]`
+
+```txt
+./check_psqlserver 
+______________________________________________________________________
+
+CHECK_PSQLSERVER :: v0.6
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+______________________________________________________________________
+
+USAGE:
+  check_psqlserver [OPTIONS] -m METHOD
+
+OPTIONS:
+  -h  this help
+  -i  install monitoring user (must be executed as root)
+  -u  uninstall monitoring user (must be executed as root)
+
+PARAMETERS:
+  -m  method; valid methods are:
+      activity        running processes and queries
+      conflicts       Detected conflicts from pg_stat_database_conflicts
+      dbrows          Count of database row actions
+      diskblock       Count of diskblocks physically read or coming from cache
+      problems        Problems and troublemakers
+      replication     Replication status (table output only)
+      transactions    Count of transactions over all databases
+
+EXAMPLES:
+  check_psqlserver -i
+  check_psqlserver -m activity
+
+```
+
+## Installation
+
+To give access to the database there is the param `-i`(for "install").
+This command needs to be run as root.
+
+```txt
+./check_psqlserver -i
+```
+
+This creates a database user "icingamonitor" with a 64 byte random password.
+To store the credentials a file file be created: `/etc/icingaclient/.psql.conf`. It is a shell script that will be sourced by check_psqlserver.
+
+```shell
+cat /etc/icingaclient/.psql.conf 
+#
+# generated on Thu Jun  8 03:44:06 CEST 2023
+#
+export PGUSER=icingamonitor
+export PGPASSWORD=87B9jUcRp38DgkLDL3uHzC3V8YjgX6KZMxIxqpWieTWWIBgNoFYt8yvK9Y8RmdL0
+export PGHOST=localhost
+
+# set default database because a user db won't be created
+export PGDATABASE=postgres
+```
+
+## Checks
+
+The checks are done on the server and summarize data from statistic tables for all databases.
+
+see <https://www.postgresql.org/docs/current/monitoring-stats.html>
+
+If you need to troubleshot and want to see which of your databases causes the trouble you can execute the statement which is ggiven in the hint.
+
+### activity
+
+Show running processes and queries
+
+```txt
+./check_psqlserver -m activity
+OK: Pgsql activity :: Running total: 33 ... active: 2 idle: 25 fastpath: 0 other: 6
+ 
+Hint: Query for details:
+select * from pg_stat_activity.
+
+ |running-total=33;; running-active=2;; running-idle=25;; running-fastpath=0;; running-other=6;; 
+```
+
+### conflicts
+
+Detected conflicts from pg_stat_database_conflicts
+
+```txt
+./check_psqlserver -m conflicts
+OK: Pgsql conflicts ::  ... OK, nothing was found
+ confl_tablespace         :               0 ... delta = 0 per min
+ confl_lock               :               0 ... delta = 0 per min
+ confl_snapshot           :               0 ... delta = 0 per min
+ confl_bufferpin          :               0 ... delta = 0 per min
+ confl_deadlock           :               0 ... delta = 0 per min
+ 
+Hint: Query for details per database:
+select * from pg_stat_database_conflicts.
+
+ |confltablespace=0;; confllock=0;; conflsnapshot=0;; conflbufferpin=0;; confldeadlock=0;; 
+```
+
+
+### dbrows
+
+Count of database row actions
+
+```txt
+./check_psqlserver -m dbrows
+OK: Pgsql dbrows :: Count of database row actions
+ tup_returned             :    744761392127 ... delta = 0 per sec
+ tup_fetched              :     21597149760 ... delta = 0 per sec
+ tup_inserted             :        42683720 ... delta = 0 per sec
+ tup_updated              :         1282902 ... delta = 0 per sec
+ tup_deleted              :         1878883 ... delta = 0 per sec
+ 
+Hint: Query for details per database:
+select * from pg_stat_database.
+
+ |tupreturned=0;; tupfetched=0;; tupinserted=0;; tupupdated=0;; tupdeleted=0;; 
+```
+
+### diskblock
+
+Count of diskblocks physically read or coming from cache
+
+```txt
+./check_psqlserver -m diskblock
+OK: Pgsql diskblock :: Count of diskblocks physically read or coming from cache (from pg_stat_database)
+ blks_read                :     20391240674 ... delta = 439 per sec
+ blks_hit                 :    103015908887 ... delta = 6549 per sec
+ 
+Hint: Query for details per database:
+select * from pg_stat_database.
+
+ |blksread=439;; blkshit=6549;;
+```
+
+### problems
+
+Problems and troublemakers
+
+```txt
+./check_psqlserver -m problems
+OK: Pgsql problems :: Problems and troublemakers (from pg_stat_database) ... OK, nothing was found
+ conflicts                :               0 ... delta = 0 per min
+ deadlocks                :               0 ... delta = 0 per min
+ checksumfailures         :               0 ... delta = 0 per min
+ temp_files               :         5617739 ... delta = 0 per min
+ temp_bytes               :   2896790521548 ... delta = 0 per min
+ 
+Hint: Query for details per database:
+select * from pg_stat_database.
+
+ |conflicts=0;; deadlocks=0;; checksumfailures=0;; tempfiles=0;; tempbytes=0;; 
+```
+
+### replication
+
+Replication status.
+
+It shows the defined replication and their status.
+It switches to state warning if one of the replications is not "streaming".
+
+Aditionally it fetches the maximum lag of write, flush and replay of all replications.
+The state switches to warning if it is larger 1 sec (just experimental).
+
+```txt
+./check_psqlserver -m replication
+OK: Pgsql replication :: status
+ OK: all replications have the state 'streaming'.
+OK: maximum lag is 0.2077 sec (below 1 sec).
+ application_name :  client_addr   :   state   :    write_lag    :    flush_lag    :  replay_lag   :    max_lag    : sync_state 
+------------------+----------------+-----------+-----------------+-----------------+---------------+---------------+------------
+ psqlbackup         : 192.168.10.21 : streaming : 00:00:00.000673 : 00:00:00.003771 : 00:00:00.2077 : 00:00:00.2077 : async
+(1 row)
+Hint: Query for details per replication:
+select * from pg_stat_replication.
+
+ |total=1;; state-streaming=1;; state-other=0;; max-lag=0.2077;; 
+```
+
+### transactions
+
+Count of transactions over all databases
+
+```txt
+./check_psqlserver -m transactions
+OK: Pgsql transactions :: Count of transactions over all databases
+ commit                   :       380856524 ... delta = 0 per sec
+ rollback                 :           13173 ... delta = 0 per sec
+ 
+Hint: Query for details per database:
+select * from pg_stat_database.
+
+ |commit=0;; rollback=0;; 
+```