marcomalva

%First Steps with Markdown %Marco Malva %2015/12/22 - 2021/05/18

Introduction

The format traditionally Markdown is now rebranded as commonmark. One can read more on commonmark here http://commonmark.org/

The commonly used suffix for markdown files is .md

marcomalva

-- PostgreSQL: List the active queries
-- see also <https://gist.github.com/rgreenjr/3637525>
SELECT ROW_NUMBER() OVER() as rn
, a.datname
, a.usename
, a.client_addr
, a.pid
, age(clock_timestamp(), a.query_start) as age_start
, age(clock_timestamp(), state_change) as age_change
, a.wait_event

marcomalva

--
-- PostgreSQL: query how larger tables (data + index) are
--
SELECT *, pg_size_pretty(total_bytes) AS total
    , pg_size_pretty(index_bytes) AS INDEX
    , pg_size_pretty(toast_bytes) AS toast
    , pg_size_pretty(table_bytes) AS TABLE
    , pg_size_pretty(sum(table_bytes) OVER(ORDER BY total_bytes)) AS table_total
    , pg_size_pretty(sum(total_bytes) OVER(ORDER BY total_bytes)) AS db_total
  FROM (

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-- show running queries (pre 9.2)
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query 
FROM pg_stat_activity 
WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%' 
ORDER BY query_start desc;

-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query 
FROM pg_stat_activity 
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' 

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# various useful nomad commands
#
# listed in pseudo pet style, i.e. "<xyz>" prompts the user to supply a value for xyz
# * [GitHub - knqyf263/pet: Simple command-line snippet manager, written in Go.](https://github.com/knqyf263/pet)
# * [document cli command options](http://docopt.org/)
# * [Utility Conventions](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_01)

# list dead jobs that are not batch (periodic)
# any job listed indicates a failed deployment, 
#    that is a deployed job that did not remain running

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-- tuning advise: https://www.cybertec-postgresql.com/en/tuning-max_connections-in-postgresql/
--

-- get number of connections by database instance + total
select datname, count(*) as cnt_conn, sum(count(*)) over () as tot_conn from pg_stat_activity group by datname order by datname;

-- get more details, see column numbackends for number of connections
select * from pg_stat_database order by datname;
select datname, numbackends, sum(numbackends) over() as tot_conn from pg_stat_database order by datname;

marcomalva

Adding an AppImage as a Gnome Application

Six steps from donwloading an appimage to making it available as a Gnome desktop application. The examples assume that one stores the appimage files in folder /opt/var/AppImage/ but any folder will do.

1. Download the appimage, e.g. cd /opt/var/AppImage/ && wget https://mirrors.mit.edu/kde/stable/digikam/7.3.0/digiKam-7.3.0-x86-64.appimage

2. Set the executable bit, e.g. chmod u+x digiKam-7.3.0-x86-64.appimage

3. Get an icon file (*.png) from the web, e.g. the github project page.

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-- copy2csv.sql: use psql to copy table or select query to CSV file with source and file as parameter
--
-- usage:
--      psql -v table_name="<table_name>" -v file_name="<file_name>" -h <host_name> -U <user_name> <db_name> -f copy2csv.sql
--      psql -v table_name="dummy" -v file_name="my_dummy.csv" -f copy2csv.sql
--      psql -v table_name="(select * from dummy order by birthdate desc)" -v file_name="my_dummy_2.csv" -f copy2csv.sql
--
-- idea from: https://postgrespro.com/list/thread-id/1893680
-- see also https://www.postgresqltutorial.com/postgresql-format/ for format command
--

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#!/bin/bash
#
# check for JVM flags pertaining periodic GC (uncommit, periodic, Shenandoa)
java -XX:+PrintFlagsFinal -version | grep -iE "uncommit|periodic|Shenandoa"

# and to show the JVM and OS settings as well the JVM version
java -XshowSettings:all -version

# testing with java8, java11 and java17
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java -XX:+PrintFlagsFinal -version | grep -iE "uncommit|periodic|Shenandoa"

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# see also: 
# * to export public key: <https://mirrors.tripadvisor.com/centos-vault/4.5/docs/html/rhel-sbs-en-4/s1-gnupg-export.html>
# * to extract private key to another machine: <https://makandracards.com/makandra-orga/37763-gpg-extract-private-key-and-import-on-different-machine>
# * to check key expiration date: <https://stackoverflow.com/questions/48914338/how-to-get-expiration-date-from-a-gpg-key>
# * to encrypt/decrypt: <https://www.gnupg.org/gph/en/manual/x110.html>
#

# list public keys
gpg --list-keys