RSKIP 559: fix pegouts ordering

Author: Vlad

IPs/RSKIP559.md

@@ -0,0 +1,39 @@
+---
+rskip: 559
+title: Deterministic next pegout selection fix
+description: Intorduce clear solution to select next pegout with enough confirmations
+status: Draft
+purpose: Sec
+author: VZ
+layer: Core
+complexity: 2
+created: 2026-04-16
+---
+
+## Abstract
+
+It was determined that we have almost non deterministic behaviour for output of the function `getNextPegoutWithEnoughConfirmations`.
+We are returning first valid match from collection which ordering is depends on JDK internal implementation.
+This is why we were having issues switching to Java 21.
+
+Such behaviour is very hard to predict and it bins nodes to exact set of JDKs.
+Replicating such behaviour in any other programming language is extremely hard.
+
+Elements ordering algorithm must be clear and easy to understand.
+
+
+## Specification & Rationale
+
+Old ordering rule is barely describable becuase it depends on ordering in 2 HashSets where one is feeded into another.
+
+New ordering just reuse existing `BTC_TX_COMPARATOR` that just use lexicographical bytes ordering of serialized transactions.
+This approach is easy, clean and understandable.
+
+
+## Backwards compatibility
+
+Changes reqires a hardfork that will turn on valid elements ordering.
+After hardfork it will be possible to extract all conflicting outputs of `getNextPegoutWithEnoughConfirmations` and hardcode them in mainnet node configuration.
+After that old ordering code will be removed.
+
+For other types of networks like future testnet v4 etc it will be required to activate this RSKIP from the block one. Testnet 3 will be morelikely dismissed till that time so no need to hardcode any outputs for it.

README.md

@@ -255,6 +255,7 @@ You can find an easily browseable version of this information [here](https://ips
 | 551 |[Deprecate RSKIP459](IPs/RSKIP551.md)| 18-MAR-26 | MI | Usa | Core | 1 | Draft |
 | 552 |[Improve Blake2F Input Validation](IPs/RSKIP552.md)| 16-MAR-2026 | FML | Sec | Core | 1 | Draft |
 | 553 |[Network Upgrade: Vetiver](IPs/RSKIP553.md)| 23-MAR-2026 | AE | Usa, Sca, Sec | Core | 2 | Draft |
+| 559 |[Fix waiting pegouts ordering](IPs/RSKIP559.md)| 16-APR-2026 | VZ | Sec | Core | 2 | Draft |
 
 # Author Index
 
@@ -293,6 +294,7 @@ You can find an easily browseable version of this information [here](https://ips
 | SM       | Shreemoy Mishra           | shreemoy@rootstocklabs.com             |
 | SMS      | Sebastian Matias Sicardi  |                                        |
 | VK       | Volodymyr Kravets         |                                        |
+| VZ       | Vladislav Zablotsky       |                                        |
 
 
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