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Automatically verify transactions in blocks when the same transaction is already in the mempool #5674

Open
Tracked by #5234
, #7366
...
teor2345 opened this issue Nov 21, 2022 · 2 comments · May be fixed by #8951
Open
Tracked by #5234
, #7366
...

Automatically verify transactions in blocks when the same transaction is already in the mempool #5674

teor2345 opened this issue Nov 21, 2022 · 2 comments · May be fixed by #8951
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@arya2
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A-rpc Area: Remote Procedure Call interfaces I-slow Problems with performance or responsiveness

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@teor2345
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teor2345 commented Nov 21, 2022 •
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Motivation

Miners need RPCs and verification to be fast, to improve profits.

When Zebra has already verified a transaction in the mempool, we know it will be valid in a block. (The mempool checks are stricter than the block transaction checks.)

So we can save time by automatically approving any block transaction verify requests that match a transaction already in the mempool.

Security

We will need to test that the mempool checks are stricter than the block transaction checks. Otherwise, we could approve invalid blocks.
This was referenced Nov 21, 2022
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@teor2345 teor2345 added I-slow Problems with performance or responsiveness P-Optional ✨ A-rpc Area: Remote Procedure Call interfaces labels Nov 21, 2022
@mpguerra mpguerra moved this to ✅ Done in Zebra Jan 24, 2023
@mpguerra mpguerra added this to Zebra Jan 24, 2023
@mpguerra mpguerra moved this from ✅ Done to 🆕 New in Zebra Jan 24, 2023
@teor2345 teor2345 changed the title Automatically verify transactions that are already in the mempool Automatically verify transactions in blocks when the same transaction is already in the mempool Apr 4, 2023
@mpguerra mpguerra mentioned this issue Aug 22, 2023
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@daira
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daira commented Aug 19, 2024

This only applies to non-contextual checks, right? Otherwise you have the following condition:

  • UTXO $u$ is not spent as of the current tip, and so a transaction $tx$ that spends $u$ can be accepted.
  • A block $B$ is mined that spends $u$ in a different transaction $tx'$, that the zebra node never accepted to the mempool.
  • Now $tx$ cannot be mined.

The same can happen for nullifiers, and for any other contextual check (e.g. mempool transactions can expire, etc.) It's fine as long as mining $B$ kicks $tx$ out of the mempool and there is no possible race condition.

@daira
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daira commented Aug 19, 2024

Ah, it sounds as though that was considered in #5376 (comment) .

@conradoplg conradoplg mentioned this issue Aug 20, 2024
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@arya2 arya2 self-assigned this Sep 30, 2024
@arya2 arya2 linked a pull request Oct 19, 2024 that will close this issue
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@mpguerra mpguerra linked a pull request Oct 21, 2024 that will close this issue
change(rpc): Avoid re-verifying transactions in blocks if those transactions are in the mempool #8951
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A-rpc Area: Remote Procedure Call interfaces I-slow Problems with performance or responsiveness
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Zebra
Status: In progress
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@daira @mpguerra @arya2 @teor2345