February 2019
Intermediate to advanced
444 pages
11h 36m
English
If we only pass the execution identifier as request metadata and tag tracing records with it, it is sufficient to reassemble that data into a single collection, but it is not sufficient to reconstruct the execution graph of causally-related activities. Tracing systems need to capture causality that allows assembling the data captured by the trace points in the correct sequence. Unfortunately, knowing which activities are truly causally-related is very difficult, even with very invasive instrumentation. Most tracing systems elect to preserve Lamport's happens-before relation [4], denoted as → and formally defined as the least strict partial order on events, such that: