Exercise 3: Why Ruling Out Retransmissions Was Still Useful — Possible Solution
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WHY RULING IT OUT WAS STILL PROGRESS
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Per this chapter, checking retransmissions in Ticket 3 produced a
"clean result... unlike Chapter 6's own worked example, packet loss
isn't the answer this time. Ruling this out is itself real progress,
not a dead end." Confirming that packet loss specifically was not
happening eliminated one entire category of explanation, narrowing what
remained to be checked - exactly the same elimination discipline used
throughout this course (ruling out CPU, memory, and disk earlier in the
same ticket), just applied to network loss specifically.

WHY A "NEGATIVE" RESULT ISN'T A DEAD END
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A check that finds nothing wrong still answers a real question - it
tells you where the problem definitely isn't, which is exactly as
useful for narrowing the search as a check that does find something,
especially once several such checks (CPU, memory, disk, packet loss)
have all come back clean and the remaining possibilities have shrunk
considerably.

THE GENUINELY NEW CHECK THAT FOUND THE REAL ANSWER
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Per this chapter, "a network check Chapter 6 didn't cover: interface
throughput" - using sar -n DEV showed the server's network interface
running at 118,000 kB/s against a roughly 125,000 kB/s (1 Gbps) rated
capacity, confirming genuine bandwidth saturation on the interface
itself, caused by a scheduled data-sync job whose timing had drifted
into overlapping with peak traffic - a different kind of network
problem (raw throughput saturation) than Chapter 6's own focus
(packet loss/retransmissions).

WHY THIS WORKS AS AN ANSWER
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It explains why a clean retransmission check still narrowed the
investigation meaningfully rather than being wasted effort, and
correctly identifies interface throughput (via sar -n DEV) as the
specific, genuinely new check that found the actual cause.