doc: add release note for #27460 (new importmempool RPC)

[theStack]

This PR adds a missing release note for #27460.

[DrahtBot]

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ACK	glozow
Stale ACK	ismaelsadeeq

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[ismaelsadeeq]

ACK 356a752

[ajtowns]

If this is going to be advertised in the release notes, shouldn't it include more warnings? eg, importing someone else's mempool.dat could result in pinning vectors so you miss out on txs being relayed across the regular network. If you enable any of the options when importing (fee deltas or unbroadcast set or time info) that could also cause problems.

[glozow]

If this is going to be advertised in the release notes, shouldn't it include more warnings? eg, importing someone else's mempool.dat could result in pinning vectors so you miss out on txs being relayed across the regular network. If you enable any of the options when importing (fee deltas or unbroadcast set or time info) that could also cause problems.

+1
Could also mention that, If you want to apply fee deltas, it is recommended to use the getprioritisedtransactions and prioritisetransaction RPCs instead of the apply_fee_delta_priority option to avoid duplicates.

[theStack]

@ajtowns: Thanks for the feedback. I added one generic warning about import untrusted files (taken from the RPC help) and @glozow's recommendation for applying fee deltas. Happy to take more suggestions.

[glozow]

LGTM, @ajtowns ?

[willcl-ark]

Could also mention that, If you want to apply fee deltas, it is recommended to use the getprioritisedtransactions and prioritisetransaction RPCs instead of the apply_fee_delta_priority option to avoid duplicates.

What exactly does "to avoid duplicates" mean here? That we can end up with two versions of the same tx in the mempool (with different deltas), or something else?

[glozow]

Could also mention that, If you want to apply fee deltas, it is recommended to use the getprioritisedtransactions and prioritisetransaction RPCs instead of the apply_fee_delta_priority option to avoid duplicates.

What exactly does "to avoid duplicates" mean here? That we can end up with two versions of the same tx in the mempool (with different deltas), or something else?

No you'll never have duplicates in your mempool. I mean it just blindly applies the deltas, so you might prioritize a transaction twice. Though I guess using the other RPC doesn't inherently prevent this; it's just a way for you to sanitize what the deltas are + check what you already have before applying them. Sentence could be dropped as it seems like it could be confusing.

[ajtowns]

LGTM, @ajtowns ?

Seems okay. Perhaps "over-prioritising" or "double counting" would work better than "duplicates".

[willcl-ark]

LGTM, @ajtowns ?

Seems okay. Perhaps "over-prioritising" or "double counting" would work better than "duplicates".

Agree. I was thinking something even more explicit though, like this:

"If you want to apply fee deltas, it is recommended to use the getprioritisedtransactions and prioritisetransaction RPCs instead of the apply_fee_delta_priority option to avoid double-prioritising any already-prioritised transactions in the mempool.

[glozow]

ACK 1b672eb