# 【etcd】写入路径深读：Txn、mod revision 与 quota/alarm

DevFeed: [【etcd】写入路径深读：Txn、mod revision 与 quota/alarm](<https://devfeed.tech/articles/etcd-txn-mod-revision-quota-alarm-33989.md>)

Original publisher: [Read original article](<https://quant67.com/post/etcd/07-write-path/07-write-path.html>)

Author: Liao Tonglang

Published: 2026-08-26T00:00:00Z

Content type: tutorial

Language: zh

Sources: [土法炼钢 - 系统与基础设施](<https://devfeed.tech/sources/source-4.md>)

Topics: [etcd](<https://devfeed.tech/topics/etcd.md>), [Back end](<https://devfeed.tech/topics/backend.md>), [Raft](<https://devfeed.tech/topics/raft.md>), [Remote Procedure Call (RPC)](<https://devfeed.tech/topics/rpc.md>), [maintenance](<https://devfeed.tech/topics/maintenance.md>)

Tags: [alarm](<https://devfeed.tech/tags/alarm.md>), [apiserver](<https://devfeed.tech/tags/apiserver.md>), [applied-index](<https://devfeed.tech/tags/applied-index.md>), [apply](<https://devfeed.tech/tags/apply.md>), [batch](<https://devfeed.tech/tags/batch.md>), [bbolt](<https://devfeed.tech/tags/bbolt.md>), [committed-index](<https://devfeed.tech/tags/committed-index.md>), [compaction](<https://devfeed.tech/tags/compaction.md>), [defrag](<https://devfeed.tech/tags/defrag.md>), [distributed](<https://devfeed.tech/tags/distributed.md>), [errcompacted](<https://devfeed.tech/tags/errcompacted.md>), [etcd](<https://devfeed.tech/tags/etcd.md>), [follower](<https://devfeed.tech/tags/follower.md>), [k8s](<https://devfeed.tech/tags/k8s.md>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [mod-revision](<https://devfeed.tech/tags/mod-revision.md>), [nospace](<https://devfeed.tech/tags/nospace.md>), [quota](<https://devfeed.tech/tags/quota.md>), [revision](<https://devfeed.tech/tags/revision.md>), [txn](<https://devfeed.tech/tags/txn.md>), [v3-5](<https://devfeed.tech/tags/v3-5.md>), [v3-5-33](<https://devfeed.tech/tags/v3-5-33.md>)

## AI overview

This tutorial explains the etcd v3.5.33 write path from gRPC requests through Raft proposal, quota checks, MVCC apply, and ModRevision assignment. It also describes proposal backpressure, backend quota accounting, and how a NOSPACE alarm blocks writes while reads, deletes, and maintenance operations can continue.

## Source excerpt

走读 etcd v3.5.33 写入路径：raftRequest 背压、Txn compare/mod 与 ModRevision 分配、backend quota 与 NOSPACE alarm 如何把集群推入只读。