Latest Articles

The Cost Of Consistency: When 9ms Is 1s Too Much

The CAP theorem remains one of the most important tools in my software developer's toolbelt. Used correctly, it can help create services and products that can offer an excellent user experience and protect revenue during partial failures. Used incorrectly, it can lead to a poor user experience and loss ... read more

Pessimistic Optimism: The Case Of Unexpected Deadlocks

Despite the fact I've been developing software in one way or another for almost 20 years, I'm constantly surprised how things work, and, once the frustration wears off, I'm intrigued when things break. Lucky for me, over the last few weeks, I've been surprised, frustrated, and ... read more

Perceiving The Effects Of Cache Coherency In Spin Locks

The "test-and-test-and-set" algorithm is a fairly well-understood solution to reducing latency in spin locks. In particular, the algorithm is often employed to reduce the latency exhibited in the similar "test-and-set" algorithm. Understanding how and why a seeming-superfluous read results in lower latency is rather interesting. ... read more

Downcasting Longs To Ints On x86

Last week, my esteemed colleague and close friend asked a remarkably straight-forward question about downcasting a long to an int in Java. I'll admit the question caught me off guard. While the JLS offered the correct answer, I couldn't help but ponder what's actually happening in the ... read more

The Concurrency Of ConcurrentHashMap

Java's ConcurrentHashMap is an excellent point of study when learning about Java's Memory Model. It employs numerous techniques to provide lock-free reads while still guaranteeing safe publication of objects. This article represents my attempt to take the magic out of the ConcurrentHashMap implementation. ... read more

see all articles

Latest Notes

Fun MySQL fact of the day: slowest sort

While we discussed yesterday that filesort can use different sorting algorithms depending on variables, we didn't discuss the various modes that filesort has. The behaviour of these modes can even make the sorting algorithm filesort chooses seem pretty unimportant. ... read more

Fun MySQL fact of the day: gorillasort

So far this week, we've been looking at ORDER BY clauses that are index-optimized away, and fun quirks aside, things have been pretty great. But what about when we can't optimize away the ORDER BY? ... read more

Fun MySQL fact of the day: uneliminating the eliminated

Yesterday, we looked at an ORDER BY leveraging index optimisation, which essentially amounted to no sorting work whatsoever. But what would happen if we changed the query just a tiny bit? We'd get a gruesomely fun fact. ... read more

Fun MySQL fact of the day: a free `ORDER`

On February 28, we discussed that the order of results from a query in the absence of an ORDER BY clause are implementation specific. We also observed that in InnoDB, this implementation-specific behaviour tends to be the order of records as they are sorted in the index from which they ... read more

Fun MySQL fact of the day: index condition pushdowns

It feels like we've been discussing Using where quite a lot lately and you might be wondering, "there must be a better way". There is. In MySQL 5.6 and beyond, queries may leverage the Index Condition Pushdown Optimisation. ... read more

Fun MySQL fact of the day: collation filtering

Yesterday, we considered some cases where MySQL may indicate Using where; Using index in the Extra field of a query plan. Today, we're going to look at one more case that existed up until MySQL 5.7, and while I haven't made a habit of digging up too ... read more

see all notes