5 ms·

Flamegraphs are wonderful. Me: looks at my code. "sure, ok, looks alright." Me: looks at the resulting flamegraph. "what the hell is this?!?!?" I've found

Flamegraphs are wonderful. Me: looks at my code. "sure, ok, looks alright." Me: looks at the resulting flamegraph. "what the hell is this?!?!?" I've found all kinds of crazy stuff in codebases this way. Static initializers that aren't static, one-line logger calls that trigger expensive serialization, heavy string-parsing calls that don't memoize patterns, etc. Unfortunately some of those are my fault.

wging 10mo ago
I also like icicle graphs for this. They're flamegraphs, but aggregated in the reverse order. (I.e. if you have calls A->B->C and D->E->C, then both calls to C are aggregated together, rather than being stacked on top of B and E respectively. It can make it easier to see what's wrong when you have a bunch of distinct codepaths that all invoke a common library where you're spending too much time.) Regular flamegraphs are good too, icicle graphs are just another tool in the toolbox.
- pests 10mo ago
  So someone else linked the original flamegraph site [0] and it describes icicle graphs as "inverting the y axis" but that's not only what's happening, right? You bucket top-down the stack opposed to bottom-up, correct? [0] https://www.brendangregg.com/flamegraphs.html https://www.brendangregg.com/flamegraphs.html
  - yxhuvud 10mo ago
    Right, what is needed is something trie-like, with the root being the most fine-grained call.
  - wging 10mo ago
    It's certainly possible that what I encountered, labeled as an 'icicle graph', is a nonstandard usage of the term. But if so, that's a shame. I don't think inverting the y-axis is useful by itself, the different bucketing is what makes for an actually useful change.
jabwd 10mo ago
I might be very wrong in every way but, string parsing and or manipulating and memoiziation... sound like a super strange combo? For the first you know you're already doing expensive allocations, but the 2nd is also not a pattern I really see apart from in JS codebases. Could you provide more context on how this actually bit you in the behind? memoizing strings seems like a complicated and error prone "welp it feels better now" territory in my mind so I'm genuinely curious.
- tyingq 10mo ago
  > but the 2nd is also not a pattern I really see apart from in JS codebases. If you're referring to "one-line logger calls that trigger expensive serialization", it's also common in java.
- shermantanktop 10mo ago
  In Java it can be a bad toString() implementation hiding behind a + used for string assembly. Or another great one: new instances of ObjectMapper created inside a method for a single call and then thrown away.
  - shermantanktop 10mo ago
    To be clear this is often sloppy code that shouldn’t have been written. But in a legacy codebase this stuff can easily happen.
    - MengerSponge 10mo ago
      A huge chunk of a "legacy codebase" is "sloppy code that shouldn’t have been written" Unless you're inheriting code written by Bill Atkinson or something.
tempaccsoz5 10mo ago
Also cool that when you open it in a new tab, the svg [0] is interactive! You can zoom in by clicking on sections, and there's a button to reset the zoom level. [0]: https://questdb.com/images/blog/2026-01-13/before.svg https://questdb.com/images/blog/2026-01-13/before.svg
- sllabres 10mo ago
  Yes, they are made with: http://www.brendangregg.com/flamegraphs.html http://www.brendangregg.com/flamegraphs.html and https://github.com/brendangregg/FlameGraph https://github.com/brendangregg/FlameGraph Useful site if you are on to perf/eBPF/performance things with many examples and descriptions even for other uses as e.g. memory usage, disk usage (prefer heatmaps here but they are nice if you want to send someone a interactive view of their directory tree ...).
sroerick 10mo ago
I've never used flamegraphs but would like to know about them. Can you explain more? Or where should I start?
- atdt 10mo ago
  Flame graphs have an official web site, maintained by Brendan Gregg, who invented them: https://www.brendangregg.com/flamegraphs.html https://www.brendangregg.com/flamegraphs.html. It's a useful starting point.
- dummydummy1234 10mo ago
  I would also try hotspot, it is a interactive viewer for perf graphs.
- jsymolon 10mo ago
  I use them all the time on Perl code. https://metacpan.org/pod/Devel::NYTProf https://metacpan.org/pod/Devel::NYTProf
arethuza 10mo ago
I always found profiling performance critical code and experimenting with optimisations to be one of the most enjoyable parts of development - probably because of the number of surprises that I encountered ("Why on Earth is that so slow?").

wging 10mo ago

I also like icicle graphs for this. They're flamegraphs, but aggregated in the reverse order. (I.e. if you have calls A->B->C and D->E->C, then both calls to C are aggregated together, rather than being stacked on top of B and E respectively. It can make it easier to see what's wrong when you have a bunch of distinct codepaths that all invoke a common library where you're spending too much time.) Regular flamegraphs are good too, icicle graphs are just another tool in the toolbox.

pests 10mo ago
So someone else linked the original flamegraph site [0] and it describes icicle graphs as "inverting the y axis" but that's not only what's happening, right? You bucket top-down the stack opposed to bottom-up, correct? [0] https://www.brendangregg.com/flamegraphs.html https://www.brendangregg.com/flamegraphs.html
- yxhuvud 10mo ago
  Right, what is needed is something trie-like, with the root being the most fine-grained call.
- wging 10mo ago
  It's certainly possible that what I encountered, labeled as an 'icicle graph', is a nonstandard usage of the term. But if so, that's a shame. I don't think inverting the y-axis is useful by itself, the different bucketing is what makes for an actually useful change.

jabwd 10mo ago

I might be very wrong in every way but, string parsing and or manipulating and memoiziation... sound like a super strange combo? For the first you know you're already doing expensive allocations, but the 2nd is also not a pattern I really see apart from in JS codebases. Could you provide more context on how this actually bit you in the behind? memoizing strings seems like a complicated and error prone "welp it feels better now" territory in my mind so I'm genuinely curious.

tyingq 10mo ago
> but the 2nd is also not a pattern I really see apart from in JS codebases. If you're referring to "one-line logger calls that trigger expensive serialization", it's also common in java.
shermantanktop 10mo ago
In Java it can be a bad toString() implementation hiding behind a + used for string assembly. Or another great one: new instances of ObjectMapper created inside a method for a single call and then thrown away.
- shermantanktop 10mo ago
  To be clear this is often sloppy code that shouldn’t have been written. But in a legacy codebase this stuff can easily happen.
  - MengerSponge 10mo ago
    A huge chunk of a "legacy codebase" is "sloppy code that shouldn’t have been written" Unless you're inheriting code written by Bill Atkinson or something.

tempaccsoz5 10mo ago

Also cool that when you open it in a new tab, the svg [0] is interactive! You can zoom in by clicking on sections, and there's a button to reset the zoom level. [0]: https://questdb.com/images/blog/2026-01-13/before.svg https://questdb.com/images/blog/2026-01-13/before.svg

sllabres 10mo ago
Yes, they are made with: http://www.brendangregg.com/flamegraphs.html http://www.brendangregg.com/flamegraphs.html and https://github.com/brendangregg/FlameGraph https://github.com/brendangregg/FlameGraph Useful site if you are on to perf/eBPF/performance things with many examples and descriptions even for other uses as e.g. memory usage, disk usage (prefer heatmaps here but they are nice if you want to send someone a interactive view of their directory tree ...).

sroerick 10mo ago

I've never used flamegraphs but would like to know about them. Can you explain more? Or where should I start?

atdt 10mo ago
Flame graphs have an official web site, maintained by Brendan Gregg, who invented them: https://www.brendangregg.com/flamegraphs.html https://www.brendangregg.com/flamegraphs.html. It's a useful starting point.
dummydummy1234 10mo ago
I would also try hotspot, it is a interactive viewer for perf graphs.
jsymolon 10mo ago
I use them all the time on Perl code. https://metacpan.org/pod/Devel::NYTProf https://metacpan.org/pod/Devel::NYTProf

arethuza 10mo ago

I always found profiling performance critical code and experimenting with optimisations to be one of the most enjoyable parts of development - probably because of the number of surprises that I encountered ("Why on Earth is that so slow?").