blockchain: Add ancestor optimization to finding Ancestor #1688
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blockchain/blockindex.go
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| heightSkip := getSkipHeight(heightWalk) | ||
| heightSkipPrev := getSkipHeight(heightWalk - 1) | ||
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| if indexWalk.ancestor != nil && |
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Quite a mouth-full of a conditional...
It also isn't immediately clear the significance (nor origin) of the -2 here.
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Got rid of everything here and changed the logic to be simpler.
idk why that -2 is there as well... Some sipa magic
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Commenting here because I just saw @Roasbeef's tweet linking to it. FYI I implemented something similar in dcrd back in 2019 in what is imo a simpler way and should be a simple backport: |
kcalvinalvin
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On startup, Ancestor call was taking a lot of time when the node was
loading the blockindex onto memory. This change speeds up the Ancestor
function significantly and speeds up the node during startup.
On testnet3 at blockheight ~2,500,000, the startup was around 30seconds
on current main and was 5 seconds with this change. Below is a benchstat
result showing the significant speedup.
goos: darwin
goarch: arm64
pkg: github.com/utreexo/utreexod/blockchain
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
Ancestor-8 120819.301µ ± 5% 7.013µ ± 19% -99.99% (p=0.000 n=10)
│ old.txt │ new.txt │
│ B/op │ B/op vs base │
Ancestor-8 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
Ancestor-8 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
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Reviving this as I noticed that the startup of a node is slowed down quite a bit by the blockindex loading. Here's a pprof of the startup blockindex loading without this PR. Here's one with the PR. Added a benchmark as well. The benchstat results were: |
This mimics the behavior of Ancestor() in bitcoind