Exercise 3: Why the Specific Date Matters More Than a General Impression — Possible Solution ==================================================================== WHAT A GENERAL IMPRESSION ACTUALLY TELLS YOU ------------------------------ "It's generally been working" is a summary judgment based on past experience or a vague sense that things have been fine - it says something about the overall track record, but nothing definitive about any one specific point in time. Per this chapter's own resolution of Chapter 1's ticket, the backup job in question had, in fact, "generally been working" for a long history before it silently started failing 21 days ago - a general impression formed from that history would have been technically accurate and still completely wrong for the actual question being asked. WHY THE ACTUAL QUESTION IS ALWAYS ABOUT ONE SPECIFIC POINT IN TIME ------------------------------ A restore request is never "has this system generally worked" - it's always "does a specific, usable backup exist from this specific date." Chapter 1's ticket needed "last night's" backup specifically; a general sense that the job usually succeeds says nothing about whether last night in particular is one of the nights it didn't. WHY A LONG SUCCESSFUL HISTORY CAN COEXIST WITH A CURRENT FAILURE ------------------------------ Per this chapter's own worked example, the job's log showed a failure starting 21 days ago with no successful run since. Every night before that failure genuinely succeeded - so "this job has a strong track record" would have been a true statement, while also being irrelevant to whether the one specific night actually needed right now succeeded. A strong general history doesn't decay retroactively just because a recent failure occurred, but it also doesn't extend forward to guarantee the failure didn't happen. WHY THIS MEANS THE ONLY RELIABLE CHECK IS THE SPECIFIC LOG ENTRY ------------------------------ Since a general impression is compatible with both "the specific night in question succeeded" and "it didn't," it can't actually answer the question a restore ticket depends on. Only checking the log entry for that exact date - as this chapter does directly, finding the job hadn't run in three weeks - can distinguish between those two possibilities. WHY THIS WORKS AS AN ANSWER ------------------------------ It explains what a general impression of reliability actually measures, explains why it's compatible with a specific recent failure existing, and explains why only checking the exact date in the log can actually answer the question a restore request depends on.