The REPL: Issue 99 - November 2022
Postgres: Safely renaming a table with no downtime using updatable views
Once again, Brandur posts a practical example of using Postgres effectively. The article covers how to rename a table safely using views. Other renames can be a bit more complicated, for example in that example, a table was renamed from
sprocket. In a typical app, there will also be foreign keys pointing to the table, named
chainweel_id(or similar). Those would still need to be renamed to
sprocket_id. Postgres includes support for generated columns:
A generated column is a special column that is always computed from other columns. Thus, it is for columns what a view is for tables.
but it doesn’t quite have all the functionality needed to be able to change a column name without down time.
Vanilla Rails is plenty
Jorge Manrubia, from 37 Signals, objects to criticism that Rails encourages poor separation of concerns. Among the things that I agree with, is that the use of plain Ruby objects (POROs) is probably underused in most application. I don’t like some of the prescriptions in the article, though.
I don’t like concerns. While it’s nice that functionality is split into it’s own file, when included in models they end up making the API of then
ActiveRecordmodel bigger. It’s already huge to start with. With large code bases, it can be very challenging knowing all the ways that ActiveRecord objects are being used. Adding more domain methods doesn’t make it better. Instead, I’ve had better luck using service objects. They make the APIs narrower. A win in my book.
In the last few years, I’ve found that separating data from functionality is one of the patterns that gives great results and scales well. Value or data objects encapsulate the data. Other classes manipulate that data. Each has it’s own lifecycle. Mixing them together is the OOO way – which Rails leans heavily on – but it tends to create very broad interfaces (see
Asdf, Direnv Together
I previously wrote about how I use asdf and dirvenv together to setup per-project postgres versions. I recently learned about asdf-direnv, a
asdfworks by creating shims of every executable. This adds some overhead. The plugin works by leveraging
direnvto change the
PATHto the actual executable, instead of the shim.
asdfto install most versions that I want to control precisely for my projects. Usually, this means the
postgresversion. Let’s time the performance without using
$ which ruby /Users/ylansegal/.asdf/shims/ruby $ time ruby -e "puts 'hello'" hello ruby -e "puts 'hello'" 0.04s user 0.02s system 38% cpu 0.155 total $ which psql /Users/ylansegal/.asdf/shims/psql $ time psql -c 'select now()' now ------------------------------- 2022-11-28 17:01:07.470615-08 (1 row) Time: 0.142 ms psql -c 'select now()' 0.01s user 0.01s system 12% cpu 0.129 total
asdf-direnvis straight forward, as listed in the documentation. Once enabled in my
$ cat .envrc use asdf watch_file ".ruby-version"
We can see the performance gains:
$ which ruby /Users/ylansegal/.asdf/installs/ruby/3.0.4/bin/ruby $ time ruby -e "puts 'hello'" hello ruby -e "puts 'hello'" 0.04s user 0.02s system 93% cpu 0.065 total $ which psql /Users/ylansegal/.asdf/installs/postgres/13.5/bin/psql $ time psql -c 'select now()' now ------------------------------- 2022-11-28 17:01:42.357192-08 (1 row) Time: 0.195 ms psql -c 'select now()' 0.00s user 0.00s system 56% cpu 0.012 total
Command With shim (s) Without shim (s) ruby 0.155 0.065 psql 0.129 0.012
In both cases, the savings are ~90 ms. It’s commonly said that anything below 200 ms is acceptable UX as “immediate”. To me, my terminal feels much snappier.
I’ve been using this setup for a few weeks. The only issue I’ve encountered was that the plugin seems to fail to pickup the occasional changes in
.ruby-toolboxeven though the documentation states that
watch_filein the documentation should fix that. I’ve been able to work around that by with
touch .envrc, which forces the
PATHto be re-calculated.
The REPL: Issue 98 - October 2022
Rebase dependent branches
Taylor Blau at the GitHub blog points highlights a new feature
git(v2.38) that I am super excited about. You can now
git rebase --update-refs. Since reading that, I’ve already saved a lot of time (and minimized mistakes) when working on a set of branches that build on each other.
Partitioning in Postgres, 2022 edition
Brandur highlights that Postgres has made great usability improvements to partitioning over the last few years. It is now relatively easy to take advantage of it.
Add Data class implementation: Simple immutable value object
An new immutable value object,
Data, has been merged into Ruby for release soon. It’s stricter than a
Struct, which in many cases is exactly what you need from a value object.
Git Monorepo Improved Performance
gitrecently shipped some performance improvements when working with large repositories, as announced on the GitHub blog.
I tested in a large repository. With default configuration:
$ time git status On branch master Your branch is behind 'origin/master' by 686 commits, and can be fast-forwarded. (use "git pull" to update your local branch) nothing to commit, working tree clean git status 0.40s user 8.55s system 429% cpu 2.082 total
We then configure
$ git config core.fsmonitor true $ git config core.untrackedcache true
And run twice, to warm up the cache:
$ time git status On branch master Your branch is behind 'origin/master' by 686 commits, and can be fast-forwarded. (use "git pull" to update your local branch) nothing to commit, working tree clean git status 0.38s user 1.43s system 159% cpu 1.141 total $ time git status On branch master Your branch is behind 'origin/master' by 686 commits, and can be fast-forwarded. (use "git pull" to update your local branch) nothing to commit, working tree clean git status 0.13s user 0.03s system 92% cpu 0.178 total
The improvement is quite significant. The end performance is under 200 ms, generally considered to be perceived as instantaneous by users. I’m thrilled!
The REPL: Issue 97 - September 2022
Signing Git Commits with Your SSH Key
SSH keys are more common than GPG keys, by far. I don’t know many developers that have GPG keys, but all of them have SSH keys, if only to use GitHub. However, the support for the signatures seems a bit rough at the moment.
Transactionally Staged Job Drains in Postgres
The article explains well how background jobs that run outside of a db transaction can have several categories or problems. However, job queues driven by relational databases sometimes don’t scale well, when compared to other queues. For example see
Sidekiq. The article presents a pattern that keeps the transactionality, but regains much of the performance by using a staging table for jobs, which drains into the actual job queue that will do the work.
Understanding GenStage back-pressure mechanism
Really concise explanation of what the concept of back-pressure means in Elixir, and how it can prevent overflow and the capacity of the system being exceeded.