addrmgr: Mitigate high CPU use when attempts become large. #3047
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This adds a missing break statement to the range over the map of addresses used to select a random entry from the map. Previously the loop would continue needlessly until the entire map was traversed. This is a minor optimization.
This updates the (*KnownAddress).chance method in the following ways: 1. Apply a lower limit to the return value. Using 0.01 as this minimum prevents tiny chance values from causing excessive iterations in (*AddrManager).GetAddress, currently the only caller. 2. Replace an inefficient loop with a single math.Pow. These changes are mitigations to excessive CPU use in the GetAddress method that manifest when the number of attempts for a KnownAddress becomes large. However, this method and much of addrmgr should be rewritten in the future since there are some ad hoc and questionable approaches to candidate address selection.
davecgh
approved these changes
Jan 20, 2023
chappjc
commented
Jan 20, 2023
| @@ -69,19 +70,18 @@ func (ka *KnownAddress) chance() float64 { | |||
| lastAttempt = 0 | |||
| } | |||
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| c := 1.0 | |||
| // Apply a lower limit to the value returned. | |||
| const minChance = 0.01 | |||
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Only thing I'm uncertain about is this const value. I haven't tested this on mainnet, but I don't see how this limit could be too high.
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I don't see any issue with it considering the total number of peers. If there were several million nodes it would probably be too high, but that isn't the case.
davecgh
changed the title
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This PR contains two commits aimed at avoiding debilitating CPU use by the
AddrManagerwhen aKnownAddress' attempts becomes large. On testnet, the dex native SPV wallet reproducibly becomes crippled without these changes, causing both high CPU use and peering timeouts as theGetAddressmethod blocks for long periods.