Update LastModifiedLedgerSeq If and Only If LedgerEntry is Modified

Preamble

CAP: 0017
Title: Update LastModifiedLedgerSeq If and Only If LedgerEntry is Modified
Author: Jonathan Jove
Status: Accepted
Created: 2019-02-01
Discussion: https://groups.google.com/forum/#!topic/stellar-dev/hzemjh1aIwc
Protocol version: TBD

Simple Summary

This proposal makes specifying and implementing the protocol easier by simplifying the semantics of LedgerEntry.lastModifiedLedgerSeq.

Abstract

It is currently possible for LedgerEntry.lastModifiedLedgerSeq to be updated by an operation even if that operation did not make any modifications to the underlying data of that LedgerEntry. This document proposes changing the semantics of lastModifiedLedgerSeq to be updated by an operation if and only if the underlying data of that LedgerEntry has changed.

Motivation

The main benefit of this proposal is that implementing the protocol would be simpler. The current behavior forces implementers to carefully manage whether lastModifiedLedgerSeq should or should not be updated in any given circumstance. The only reliable way for an implementer to determine when lastModifiedLedgerSeq should be updated in the current protocol version is by referring to an existing implementation. This proposal would unambiguously specify when lastModifiedLedgerSeq should and should not be updated.

For example, using AllowTrust to authorize a trustline that is already authorized will update the lastModifiedLedgerSeq of the trustline without making any other modifications. In contrast, a tentative winner of Inflation that ends up winning nothing (due to, for example, having excessive native asset liabilities) is unchanged and does not receive an updated lastModifiedLedgerSeq.

Specification

The value of lastModifiedLedgerSeq should be updated by an operation if and only if the net effect of that operation includes updating the underlying data of a LedgerEntry. Specifically, if leBefore and leAfter are the LedgerEntry (excluding lastModifiedLedgerSeq) before and after the operation has been applied, respectively, then lastModifiedLedgerSeq should be updated to LedgerHeader.ledgerSeq if and only if leBefore != leAfter.

Rationale

This proposal is to be applied at the operation level as it guarantees that if the net effect of any operation in a transaction set includes updating the underlying data of a LedgerEntry then the value of lastModifiedLedgerSeq will be updated. This behavior is desirable from an implementation perspective because it allows each operation to correctly determine whether lastModifiedLedgerSeq should be updated without any knowledge of whether the LedgerEntry has been or will be modified by other operations in the same transaction set.

Backwards Compatibility

Downstream systems which rely on lastModifiedLedgerSeq could be effected as the semantics of that field will change.

Test Cases

None yet.

Implementation

No implementation yet.