Evan Jones - Software Engineer | Computer Scientist

You can't safely use the C setenv() or unsetenv() functions in a program that uses threads. Those functions modify global state, and can cause other threads calling getenv() to crash. This also c...

https://www.evanjones.ca/setenv-is-not-thread-safe.html

This is a reminder that random load balancing is unevenly distributed. If we distribute a set of items randomly across a set of servers (e.g. by hashing, or by randomly selecting a server), the a...

https://www.evanjones.ca/random-load-balancing-is-uneven.html

I was wondering: how often do nanosecond timestamps collide on modern systems? The answer is: very often, like 5% of all samples, when reading the clock on all 4 physical cores at the same time. ...

https://www.evanjones.ca/nanosecond-collisions.html

The read() and write() system calls take a variable-length byte array as an argument. As a simplified model, the time for the system call should be some constant "per-call" time, plus time direct...

https://www.evanjones.ca/read-write-buffer-size.html

This is a post for myself, because I wasted a lot of time understanding this bug, and I want to be able to remember it in the future. I expect close to zero others to be interested. The C standar...

https://www.evanjones.ca/isspace_locale.html

Nearly all programs are written to access virtual memory addresses, which the CPU must translate to physical addresses. These translations are usually fast because the mappings are cached in the ...

https://www.evanjones.ca/hugepages-are-a-good-idea.html

Let's imagine we have an program that stores its state in a database, and we want other programs to do things when changes occur. For example, we might want to send email notifications if a bank ...

https://www.evanjones.ca/replicating-db-to-queue.html

The Go "functional options" pattern is a way of passing options to a function. The function takes a variable number of arguments, which are themselves functions (a type like ...func(*config). I t...

https://www.evanjones.ca/go-functional-options-slow.html

Following up on my last post about large JSON queries , I also benchmarked sub-string queries on large variable-length strings. I wanted to check if sub-string queries might be faster than HSTORE...

https://www.evanjones.ca/postgres-large-string-performance.html

Postgres supports three types for "schemaless" data: JSON (added in 9.2), JSONB (added in 9.4), and HSTORE (added in 8.2 as an extension). Unfortunately, the performance of queries of all thre...

https://www.evanjones.ca/postgres-large-json-performance.html