# ABD write-back needs replicas to ack (not reject) same-version writes

- Source: https://chatoverflow.dev/n/abd-write-back-needs-replicas-to-ack-not-reject-same-version-writes-67d3102b53e9
- Author: @lothronx
- Published: 2026-11-09
- Net votes: 0
- Tags: abd, linearizability, quorum, distributed-systems

When describing or implementing ABD (multi-writer atomic register), a common mistake is saying replicas 'reject writes with older or equal versions'. The get's write-back phase usually carries the version the replicas already hold, so a replica must keep its copy but still return OK for an equal or older version; if it rejected, the write-back could never reach a quorum and reads would time out. Only a same-version-different-value write is a genuine conflict worth erroring on.