Sunday, July 24, 2016

Microservices mishaps: 1 query, multiple DBs

I want to share my experience with the latest trend in software engineering - microservices.

In particular, I want to explain a case I recently stumbled upon which made us hate the strategy we've got of splitting the big monolithic application to microservices.

The use case is relatively simple - one wants to make a query concerning multiple entities. They have relations between them nevertheless, the data ideally should be owned by separate microservices in an autonomous way.

The example:

Let's say that the product is a ERP-like and naturally we would have entities like company and invoices. Naturally, we'd went for microservice for the company - let's name it company-srv and one for invoices - invoice-srv. Both of these should own the APIs and DB

Now what happens when we want to make a query that is something like:
Get all companies with more than 1000 invoices
or slightly more complex example:
Get all invoices that haven't sent email-report last month for the companies that have this feature enabled.

How do you handle such responsibility - is it in invoice-srv's ownership and it should have a dependency on the other services? How do you keep the performance high with increased row count?

Even if you handle this with additional relations between the 2 DBs between the autonomous services, let's add another more interesting factor to the situations.

The more complex (and quite common) example:

Let's try to intertwine permissions - let's say that the user who is trying to see the results of the above queries, doesn't have permissions for some of the companies? Or even more intriguing - for some of the branches of the companies...

Whose responsibility is it to orchestrate the query? Does it become a multi-query operation? Is there going to be a permissions-srv ? What about performance?  Pagination?


All these are questions we ask when we pick microservices. Otherwise, it would have been a simple JOIN in the monolithic approach....

Are we going backwards? :)

more on the topic this cool post: 

Friday, June 03, 2016

Old projects reborn - MoneyTimer

This is another tool, I've tried to update in order to withstand the test of time - MoneyTimer

What does it do ?
It measures time and calculates every second how much time it costed all participants.
Great for consultation meetings!

You can try out the latest release here:

What I can learn from it?
- Java 8 Lambda expressions
- Simple Multi-threaded application
- Swing

How to contribute: 
Check the instructions at the github repo page.
If you are wondering what to contribute: there's a list of ideas in the issues page

Tune in, because more complex ones are coming ...

Check out my other project that can interest you. This time about HTML generation via XSL transformations -

Friday, April 29, 2016

Old projects reborn - FileSystem2Html tool

As everyone in the IT business, I have quite a few of my own projects. Most of them rot in solitude and are rather dusty... So, I decided as a way of exercise as well as a check how have technologies developed and my own views on code cleanness, tests' quality and overall project usability, to make them more development-friendly.

In short - I'm reviving my projects (both university and personal ones) so that they are easy to setup, run and contribute to if there's a willing person.

I'm starting with this small project:

What does it do:

- it's a simple Folder structure scanner
- it can build an HTML/XML report of the folder structure
- it can rebuild that folder structure elsewhere (without the content, obviously)

My "beautiful" swing UI

Very useful if you like a certain folder structure, and don't have the time to remove all the files or whatever. You can easily mimic it. Quite a simple app.

Now to the contribution part:

- It's an open source project 
- Java 8 required
- built with Maven 
- a list of TODOs and ideas where one can get started! I've listed ideas based on effort. 
I would start with the small ones

The project builds automatically and measures code coverage (yes, there are unit tests there!)
(Thank you Travis-CI, Coveralls and Coverity!)

So that's pretty much it.
I can't wait until I see someone energetic about such a tool

Best of wishes!

Please be gentle :) I know there's some pretty lame code out there!