Time seems simple. But we engineers lose sleep over something as basic as keeping clocks in sync. Here’s why…
The answer lies in this one simple statement - there is no global clock. When you have thousands of machines spread across data centers, continents, and time zones, each operating independently, the simple question of “what time is it?” becomes surprisingly complex.
Clock synchronization sits at the core of some of the most challenging problems in distributed systems, affecting everything from database consistency to debugging to financial transactions.
Let’s dig deeper…
The Illusion of Accurate Time
Every computer has an internal clock, typically driven by a quartz crystal oscillator. These oscillators work by vibrating at a specific frequency when voltage is applied. The standard frequency for most computer clocks is 32768 Hz, chosen because it is a power of two and makes counting down to one second straightforward.
The catch: quartz crystals are not perfect. Their oscillation frequency varies based on many factors; here are a few…
Temperature is the biggest culprit. Standard quartz crystals exhibit frequency drift in the tens of parts per million when temperature changes. A temperature deviation of ~10 degrees Celsius can cause drift equivalent to about 110 seconds per year. The crystal vibrates faster or slower depending on ambient temperature, and data center environments are not perfectly controlled.
Another culprit is manufacturing variation. No two crystals are identical. Even crystals from the same production batch will have slightly different characteristics. Aging compounds this problem as crystals change properties over time.
The result is that two computers started at exactly the same time, never communicating with each other, will inevitably drift apart. After just one day, they might differ by hundreds of milliseconds. After a month, they could be seconds apart.
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