In this project I was extending legacy code of project that optimized worker schedules. I did almost all of the technical work.

What was the challenge:

• Application had a lot of technical debt at the start of the project. IMO I decreased amount of debt;
• Performance budget was almost spent in previous iteration, so I needed to make sure that I won't make things slower;
• I needed to maintain good backwards compatibility;

What went well:

• Maintaining backwards compatibility;
• Very little bugs new bugs introduced;
• Significantly reduced amount of existing bugs;

What didn't went well:

• This was a project with tight timeline, if I had more time (or just took more risks) I could probably remove much more debt, and improve performance.
• I did introduced a lot of tests, but still unit-test coverage is bad (most of issues will come out in integration tests, though, but guessing what went wrong was not straightforward;

If you are interested in more technical conclusions see here.