Refactor live "/:username", ProfileLive

[wintermeyer]

Feed the database with the demo users and load a /:username page in your browser. Have a look at the millions of SQL queries which are triggered by that page.

I am sure that there is a massive potential to DRY that code and to improve it. No need to load the same data over and over again from the database.

@briankariuki Please do create sub issues when it makes sense. I prefer small and quick over big PRs since everybody else is working on the same code.

PS: Please add a before/after time when possible. I would like to get a feeling how much performance we gain with this issue.

Tasks

• Refactor Story resource #1030
• Refactor user_flags #1031
• Refactor how random_interests are loaded in top_navigation_component #1033
• Refactor User, BasicUser resource #1028
• Refactor the mount/3 functions in profile_live #1049
• Add action to user_flags that loads the intersecting flags between two users based on color #1056
• Refactor loading flags (counts, intersecting) in profile_live #1054
• Refactor profile_live

[wintermeyer]

Code readability is a major point too. Since the application is online now more people look into the code. They should have a chance to understand it.

[briankariuki]

Let me investigate what's causing the issue. I'll add the findings here before attempting to fix it

[briankariuki]

The first issue I've noticed is the read :by_user_id action on the Story resource.
It loads the user, which is redundant as already the user_id is passed. The User resource loads a few things when its built which require reading from the database. Hence the many sql query reads for each story fetched with the user preloaded.

I can go ahead and refactor the Story resource not to load the user or do it on the profile_stories_live.ex where we fetch the stories and use the :read action and preload only what we need to display that page.

@wintermeyer what do you think?

[briankariuki]

The second issue I found is that the UserFlags resource also preloads the user.

[wintermeyer]

@wintermeyer what do you think?

I can't say much about it because I am not deep in the code. I just see all the SQL queries in the log and always think "this can not be the optimal way of doing it". Within the Phoenix world SQL queries are expensive (at least 9 out of 10 times). I am saying this because I used to program a lot with Ruby on Rails and there SQL was much cheaper than Ruby. But for us normal Elixir is cheaper than multiple SQL queries.

Bottom line: Do what makes most sense for you to get more speed and improve readability (hoping that both come together). In case you have to make a choice between speed and code readability I tend to go into the code readability direction.

[wintermeyer]

In my opinion the /:username ProfileLive should not need more than 2-4 SQL queries. In a perfect world it should only need 1 but let's be realistic.

[wintermeyer]

The second issue I found is that the UserFlags resource also preloads the user.

Please keep #1002 in mind while working with the flags.

[wintermeyer]

@briankariuki Please do me a favour and set the in progress flag to this issue while you are working on it. Thanks!