火焰图（Flame Graphs）

Posted 2023-04-19

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参考技术A 火焰图（Flame Graph）是由 Linux 性能优化大师 Brendan Gregg 发明的，和所有其他的 profiling 方法不同的是，火焰图以一个全局的视野来看待时间分布，它从底部往顶部，列出所有可能导致性能瓶颈的调用栈。

火焰图整个图形看起来就像一个跳动的火焰，这就是它名字的由来：

常见的火焰图类型有 On-CPU，Off-CPU，还有 Memory，Hot/Cold，Differential 。

多练习：进行性能优化有意识的使用火焰图的方式进行性能调优（如果时间充裕）

Github上有 Brendan D. Gregg 的 Flame Graph 工程实现了一套生成火焰图的脚本.我们可以直接克隆下来直接用。

生成火焰图，一般遵循一下流程：

JAVA 图作业算法实现代写Graphs 数据结构作业

JAVA 图作业算法实现、代写Graphs 数据结构作业
Lab Case – Algorithms and Data Structure, 2017-2018
Phase 3. Graphs
Currently, SharingCar only provides service in ten cities (Madrid, Barcelona,
Valencia, Sevilla, Bilbao, Granada, Toledo, Salamanca, Alicante, Cáceres). Note: you
can ignore the accents.
Every day, SharingCar creates a map with all its travels offered in order to know
the possible connections between cities.
Implement a graph, whose vertices are the cities (you must use an array of String
to store the vertices. In this way, each city is represented by a index from 0 to 9).
Please, take into account that, for example, the offer (Madrid, Barcelona) is not
equal to (Barcelona, Madrid). The class must contain the following methods:
? A constructor method that takes an array of cities and build the basic
structure to create the graph.
? A method, setTravels(LstRequest offers), that takes a list of offers to create
the edges of the graph with the offered travels. For example, if an offer
provides a travel between Madrid (0) and Barcelona (1), the method must
create an edge (with weight equals to 1) between these two vertices. If the
edge already exists, then the method only has to increase its associated
weight. In other words, an edge represents the number of offered travels
from a city to another. Please, explain its time complexity (Big-O function).
? A method, getListDestination(String city), that takes a city and returns all
possible destinations. Please, explain its time complexity (Big-O function).
? A method, getListOrigin(String city), that takes a city and returns all
possible origin to this city. Please, explain its time complexity (Big-O
function).
? A method, getAllCities(), returning all cities in the graph obtained through
a depth traversal.
? A method, nonConnectedCities() that returns a list of cities which are not
connected (there is no path between them). For example, Sevilla is
connected to Barcelona via Toledo and Madrid, but there is no travel from
Barcelona to Sevilla, so (Barcelona, Sevilla) must be part of the returned list.
? Please, explain the space complexity of your data structure.
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