Stopping a blocking query in postgresql

Problem

You run a query in PostgreSQL that takes a lot of time to finish (maybe because of an error) and you want to stop/kill it as it is blocking other queries in db.

Solution

You will need to find the pid for the query, either by using a GUI program like Pgadmin or by issuing the following to an SQL prompt:

make a note of the pid of the query that you want to stop/kill and issue the following:

(issues) lib/issues/github_issues.ex:14: Issues.GithubIssues.handle_response({:error, %HTTPoison.Error{id: nil, reason: :connect_timeout}})

Problem

Trying to follow the example in ‘Programming Elixir 1.2’ for fetching the issues from Github you are getting the following error:

Solution

You are quite likely behind a proxy and you get a timeout. Add the proxy details to the HTTPoison.get request as follows:

And you could make the following change to the github_issues.ex file to be able to work with the proxy:

So you can call it like the following from iex:

function for getting the bitmask integer value in PostgreSQL

Problem

You have set up some bitmask values and you would like to return the calculated value given a string with one or more of the codes used, to be able to used it in an SQL query.

Solution

You can use the following to create a function called bitmask. This one deals with any number of individual codes (2 and 3 digit codes in this case).
It also does not calculate duplicate values since they are removed.
So for this example the string ’02a’ is the same as ’02a,02a’ and should give 16 in both cases.

ActiveRecord::InvalidForeignKey: PG::ForeignKeyViolation: ERROR: …

Problem

You have a Ruby on Rails application/engine with some tests in Minitest and using postgresql as the db. In the original development environment all the tests that use fixtures and foreign key validations pass, but when you try to move to a different environment with new database some or all of you tests fail with a message that refers to the ForeignKeyViolation as in:

Solution

Since active record disables the foreign keys before loading the fixtures in the database, the user that you run the tests with needs to have superuser permissions in the test database. Otherwise the fixtures are not loaded. So add the superuser permissions to your user:

You may need to drop and create your test database.

unhandled &1 outside of a capture

Problem

Running something like the following in iex:

results in the following error:

Solution

Since the shortcut has been changed you will need to do the following:

Request failed (404) ** (Mix) Package fetch failed and no cached copy available

Problem

You are trying to use hex for installing dependencies but when you are behind a proxy you get the following message:

Solution

You can use the following to set up hex (taken from the answer here:

Error: Brunch 2+ requires node v4.0+. Upgrade node or use older brunch for old node.js: npm i -g brunch@1

Problem

Trying to start a new phoenix application while your node installation is old you get the following error:

Solution

You will need to upgrade your node installation by following the steps below:

Running a specific Cop in Rubocop

Problem

You are working on an existing rails project with many rubocop warnings and you would like to fix certain types or warnings by getting only the specified files.

Solution

So for example when you use rubocop you first get the following for all the files in the project:

You can get a grouping of the errors by using the following:

If you would like to know only the files for a certain type of warning to be able to fix them you could try the following:

Using Array.wrap in Rails when the results could either be a string or an array

Problem

You want to use some array method in a value returned, which can either be a single value or an array of values.

Solution

Rails ActiveSupport Array, provides a method called wrap, that can be used to:

Wraps its argument in an array unless it is already an array (or array-like)

Full explanation of the method here.

Thanks Miles

Converting number from any base system to decimal in linux shell

Problem

You would like to quickly convert a number from a different base system (i.e. binary, octal, hexadecimal), to decimal.

Solution

Use the echo $(()) shell command to convert it passing it the current base system and the number, as in $((2#101010)) or using the O for octal or 0x for hexadecimal notations.
Examples:

Taken from Linux Journal’s Work the Shell column (March 2016)