system-design

I want to design a job scheduler cluster, which contains several hosts to do cron job scheduling. For example, a job which needs run every 5 minutes is submitted to the cluster, the cluster should point out which host to fire next run, making sure: Disaster tolerance: if not all of the hosts are down, the job should be fired successfully. Validity: only one host to fire next job run. Due to disaster tolerance, job cannot bind to a specific host. One way is all the hosts polling a DB table(certainly with lock), this guaranteed only one host gets the next job run. Since it often locks table, is

The major shortcomings with Entity-Attribute-Value database designs in SQL all seem to be related to being able to query and report on the data efficiently and quickly. Most of the information I read on the subject warn against implementing EAV due to these problems and the commonality of querying/reporting for almost all applications. I am currently designing a system where the fields for one of the entities are not known at design/compile time and are defined by the end-user of the system. EAV seems like a good fit for this requirement but due to the problems I've read about, I am hesitant

In Swift, I have historically used extensions to extend closed types and provide handy, logic-less functionality, like animations, math extensions etc. However, since extensions are hard dependencies sprinkled all over your code-base, I always think three times before implementing something as an extension. Lately, though, I have seen that Apple suggests using extensions to an even greater extent, e.g. implementing protocols as separate extensions. That is, if you have a class A that implement protocol B, you end up with this design: class A { // Initializers, stored properties etc. }

I have been working with PHP for years and gotten a very good grasp of the language, created many advanced and not-so-advanced systems that are working very well. The problem I'm running into is that I only learn when I find a need for something that I haven't learned before. This causes me to look up solutions and other code that handles the problem, and so I will learn about a new function or structure that I hadn't seen before. It is in this way that I have learned many of my better techniques (such as studying classes put out by Amazon, Google or other major companies). The main problem