Use non-aggregated data when generating the flamegraph. #219
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This will help reduce the number of flame towers with wide blocks on top of narrow ones, allowing us to upgrade d3.flamegraph more easily. We can't entirely remove the wide blocks on top of narrow ones, as xhprof does not expose enough data for deeply nested call stacks. We could apply heuristics to ensure that a child is always lesser than its parent, but we will report data inaccurately with that approach.
Krinkle
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This unfortunately never worked correctly due to a fundamental limitation with the XHProf data format, which is that it only records metadata per parent-child method combination, it cannot be used to build a complete call tree. The feature was added in pull perftools#177. More information about this limitation is described in detail at perftools#219, perftools#216 and perftools#212. A brief summary: * The visualisation showed callstacks that did not actually exist, and was missing callstacks that did exist. (Due to assuming that every combination of a parent-child pair is valid, and due to it randomly assinging repeated calls to the first encountered parent.) * The visualisation discarded all timing values from XHProf, except for the timing of leaf nodes (methods without children), which were then added up recursively. The end result was a visually well-balanced tree, but with timing values that were not related to the actual performance (upto 100x inflated), and the proportions were incorrect as well, making some code look fast instead of slow, and vice versa. These are inherent problems that cannot be solved because the information logically required to make a flamegraph (call stacks) is not collected by XHProf. This closes perftools#216, perftools#212, perftools#211, perftools#207. This fixes perftools#212.
Krinkle
added a commit
to Krinkle/xhgui
that referenced
this pull request
Sep 23, 2018
This unfortunately never worked correctly due to a fundamental limitation with the XHProf data format, which is that it only records metadata per parent-child method combination, it cannot be used to build a complete call tree. The feature was added in pull perftools#177. More information about this limitation is described in detail at perftools#219, perftools#216 and perftools#212. A brief summary: * The visualisation showed callstacks that did not actually exist, and was missing callstacks that did exist. (Due to assuming that every combination of a parent-child pair is valid, and due to it randomly assinging repeated calls to the first encountered parent.) * The visualisation discarded all timing values from XHProf, except for the timing of leaf nodes (methods without children), which were then added up recursively. The end result was a visually well-balanced tree, but with timing values that were not related to the actual performance (upto 100x inflated), and the proportions were incorrect as well, making some code look fast instead of slow, and vice versa. These are inherent problems that cannot be solved because the information logically required to make a flamegraph (call stacks) is not collected by XHProf. This closes perftools#216, perftools#212, perftools#211, perftools#207. This fixes perftools#212.
Krinkle
added a commit
to Krinkle/xhgui
that referenced
this pull request
Sep 23, 2018
This unfortunately never worked correctly due to a fundamental limitation with the XHProf data format, which is that it only records metadata per parent-child method combination, it cannot be used to build a complete call tree. The feature was added in pull perftools#177. More information about this limitation is described in detail at perftools#219, perftools#216 and perftools#212. A brief summary: * The visualisation showed callstacks that did not actually exist, and was missing callstacks that did exist. (Due to assuming that every combination of a parent-child pair is valid, and due to it randomly assinging repeated calls to the first encountered parent.) * The visualisation discarded all timing values from XHProf, except for the timing of leaf nodes (methods without children), which were then added up recursively. The end result was a visually well-balanced tree, but with timing values that were not related to the actual performance (upto 100x inflated), and the proportions were incorrect as well, making some code look fast instead of slow, and vice versa. These are inherent problems that cannot be solved because the information logically required to make a flamegraph (call stacks) is not collected by XHProf. This closes perftools#212, perftools#211, perftools#207. This fixes perftools#212.
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This will help reduce the number of flame towers with wide blocks on top of narrow ones, allowing us to upgrade d3.flamegraph more easily.
We can't entirely remove the wide blocks on top of narrow ones, as xhprof does not expose enough data for deeply nested call stacks. We could apply heuristics to ensure that a child is always lesser than its parent, but we will report data inaccurately with that approach.
Refs #216