Andrei Kurhan casperbrike

To list all python versions in default locations

ls /usr/bin/python*

To remove just python3 package

sudo apt-get remove python3.5

plus it's dependent packages

sudo apt-get remove --auto-remove python3.5

plus configuration and/or data files of python3

sudo apt-get purge python3.5

List of sites with free tier limits

Docker Hub - One private repo/image spot for free
Three Scale - Very generous free tier 50GB of space, 500 Pulls a month etc..
Canister - 20 private repos with almost no limits on free tier
Code Fresh - Free tier for developers

Setup your own private registry

Setup Private Docker Registry - Digital Ocean hosted Tutorial

Retry count	Retry Time	Total Cumulative Time	Total Cumulative Days
0	0:00:00	0:00:00	0.0
1	0:00:16	0:00:16	0.0
2	0:00:31	0:00:47	0.0
3	0:01:36	0:02:23	0.0
4	0:04:31	0:06:54	0.0
5	0:10:40	0:17:34	0.0
6	0:21:51	0:39:25	0.0
7	0:40:16	1:19:41	0.1
8	1:08:31	2:28:12	0.1

Optimistic Locking assumes that a database transaction conflict is very rare to happen. It uses a version number of the record to track the changes. It raise an error when other user tries to update the record while it is lock.

usage

Just add a lock_version column to the table you want to place the lock and Rails will automatically check this column before updating the record.

Pessimistic locking assumes that database transaction conflict is very likely to happen. It locks the record until the transaction is done. If the record is currently lock and the other user make a transaction, that second transaction will wait until the lock in first transaction is release.

usage

	# save this file in /etc/default/unicorn_app
	USER=app_user
	APP_ROOT=/srv/app
	RVM_STRING=2.2.4@app_gemset
	RACK_ENV=production
	UNICORN_OPTS="-D -c /srv/app/shared/config/unicorn.rb -E production"
	DAEMON=unicorn

	# (I recommend understanding the basics of this first: http://sequel.jeremyevans.net/rdoc/files/doc/object_model_rdoc.html)

	# Extending the underlying dataset (http://sequel.jeremyevans.net/rdoc/files/README_rdoc.html#label-Extending+the+underlying+dataset)

	# The recommended way to implement table-wide logic by defining methods on the dataset using dataset_module:

	class Post < Sequel::Model
	dataset_module do
	def posts_with_few_comments
	where{num_comments < 30}

	# Boolean
	op.add_column('projects', sa.Column('is_closed', sa.Boolean(), server_default=sa.schema.DefaultClause("0"), nullable=False))

	# DateTime
	op.add_column('projects_users', sa.Column('created_at', sa.DateTime(), server_default=sa.func.current_timestamp(), nullable=False))

	HTTP status code symbols for Rails

	Thanks to Cody Fauser for this list of HTTP responce codes and their Ruby on Rails symbol mappings.

	Status Code Symbol
	1xx Informational
	100 :continue
	101 :switching_protocols
	102 :processing

	ewoJInNpZ25hdHVyZSIgPSAiQXBNVUJDODZBbHpOaWtWNVl0clpBTWlKUWJLOEVk
	ZVhrNjNrV0JBWHpsQzhkWEd1anE0N1puSVlLb0ZFMW9OL0ZTOGNYbEZmcDlZWHQ5
	aU1CZEwyNTBsUlJtaU5HYnloaXRyeVlWQVFvcmkzMlc5YVIwVDhML2FZVkJkZlcr
	T3kvUXlQWkVtb05LeGhudDJXTlNVRG9VaFo4Wis0cFA3MHBlNWtVUWxiZElWaEFB
	QURWekNDQTFNd2dnSTdvQU1DQVFJQ0NHVVVrVTNaV0FTMU1BMEdDU3FHU0liM0RR
	RUJCUVVBTUg4eEN6QUpCZ05WQkFZVEFsVlRNUk13RVFZRFZRUUtEQXBCY0hCc1pT
	QkpibU11TVNZd0pBWURWUVFMREIxQmNIQnNaU0JEWlhKMGFXWnBZMkYwYVc5dUlF
	RjFkR2h2Y21sMGVURXpNREVHQTFVRUF3d3FRWEJ3YkdVZ2FWUjFibVZ6SUZOMGIz
	SmxJRU5sY25ScFptbGpZWFJwYjI0Z1FYVjBhRzl5YVhSNU1CNFhEVEE1TURZeE5U
	SXlNRFUxTmxvWERURTBNRFl4TkRJeU1EVTFObG93WkRFak1DRUdBMVVFQXd3YVVI

	release: bin/release
	web: ...
	worker: ...