# lag

Published articles for lag.

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## Detecting Replica Lag That Breaks Read-Your-Writes Consistency

DevFeed: [Detecting Replica Lag That Breaks Read-Your-Writes Consistency](<https://devfeed.tech/articles/the-replica-lag-you-do-not-measure-is-the-one-serving-checkout-39596.md>)

Original publisher: [Read original article](<https://ankit-rana.com/logs/44-replica-lag-read-your-writes/>)

Author: hello@ankit-rana.com

Published: 2026-08-28T00:00:00Z

Content type: tutorial

Language: en

Sources: [Ankit Rana | Mechanical Sympathy](<https://devfeed.tech/sources/ankit-rana-mechanical-sympathy.md>)

Topics: [Replication](<https://devfeed.tech/topics/replication.md>), [Routing (disambiguation)](<https://devfeed.tech/topics/routing.md>)

Tags: [checkout](<https://devfeed.tech/tags/checkout.md>), [consistency](<https://devfeed.tech/tags/consistency.md>), [lag](<https://devfeed.tech/tags/lag.md>), [metric](<https://devfeed.tech/tags/metric.md>), [observability](<https://devfeed.tech/tags/observability.md>), [postgresql](<https://devfeed.tech/tags/postgresql.md>), [primary](<https://devfeed.tech/tags/primary.md>), [read-replica](<https://devfeed.tech/tags/read-replica.md>), [read-replicas](<https://devfeed.tech/tags/read-replicas.md>), [replica-lag](<https://devfeed.tech/tags/replica-lag.md>), [replication](<https://devfeed.tech/tags/replication.md>), [routing](<https://devfeed.tech/tags/routing.md>)

### AI overview

This article explains how read replicas can break read-your-writes behavior when applications do not route related reads to the primary or wait for replication. It compares byte lag with time lag, explains why idle systems can hide failures, and discusses replay delays caused by write bursts and long-running replica queries.

### Source excerpt

Byte lag between primary and replica reads zero on an idle primary even when replication is completely stuck, so the metric that looks healthiest is the one that hides the failure. Time lag measured from the last replayed transaction is the signal that stays honest. Adding a read replica silently removes read-your-writes, which means any flow that writes and then reads back needs either primary routing or an explicit wait for the replica to reach that write's log position.

## 【kube-apiserver】APF 与 max-in-flight：公平排队、504 与 etcd lag 分列

DevFeed: [【kube-apiserver】APF 与 max-in-flight：公平排队、504 与 etcd lag 分列](<https://devfeed.tech/articles/kube-apiserver-apf-max-in-flight-504-etcd-lag-33968.md>)

Original publisher: [Read original article](<https://quant67.com/post/apiserver/12-apf/12-apf.html>)

Author: Liao Tonglang

Published: 2026-08-28T00:00:00Z

Content type: article

Language: zh

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

Topics: [Kubernetes](<https://devfeed.tech/topics/kubernetes.md>), [API](<https://devfeed.tech/topics/api.md>), [SRE](<https://devfeed.tech/topics/sre.md>), [Linux](<https://devfeed.tech/topics/linux.md>)

Tags: [apf](<https://devfeed.tech/tags/apf.md>), [api](<https://devfeed.tech/tags/api.md>), [apiserver](<https://devfeed.tech/tags/apiserver.md>), [distributed](<https://devfeed.tech/tags/distributed.md>), [etcd](<https://devfeed.tech/tags/etcd.md>), [fairness](<https://devfeed.tech/tags/fairness.md>), [fairqueuing](<https://devfeed.tech/tags/fairqueuing.md>), [flowcontrol](<https://devfeed.tech/tags/flowcontrol.md>), [k8s](<https://devfeed.tech/tags/k8s.md>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [lag](<https://devfeed.tech/tags/lag.md>), [max-in-flight](<https://devfeed.tech/tags/max-in-flight.md>), [priority](<https://devfeed.tech/tags/priority.md>), [timeout](<https://devfeed.tech/tags/timeout.md>), [v1-30-3](<https://devfeed.tech/tags/v1-30-3.md>)

### AI overview

This article explains how Kubernetes v1.30.3 protects kube-apiserver from overload through API Priority and Fairness (APF) and the older max-in-flight limits. It distinguishes 429 responses, APF queue timeouts that can produce 504 responses before storage is reached, etcd latency, and admission webhook delays, and describes APF's FlowSchema, PriorityLevelConfiguration, fair queuing, and shuffle sharding mechanisms.

### Source excerpt

钉 K8s v1.30.3 的 API Priority and Fairness（APF）：FlowSchema 匹配、PriorityLevelConfiguration 公平排队（SFVR）、与旧 max-in-flight flag 的共存关系；429/timeout/504 在 APF 排队、etcd_request_duration_seconds、Admission Webhook 三轴的分列；pkg/util/flowcontrol 路径；APF 与简单 max-in-flight 的运维复杂度争论。

## 【etcd】Watch 机制：watchableStore、synced/unsynced 与 ErrCompacted

DevFeed: [【etcd】Watch 机制：watchableStore、synced/unsynced 与 ErrCompacted](<https://devfeed.tech/articles/etcd-watch-watchablestore-synced-unsynced-errcompacted-33991.md>)

Original publisher: [Read original article](<https://quant67.com/post/etcd/09-watch/09-watch.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>), [Raft](<https://devfeed.tech/topics/raft.md>), [Remote Procedure Call (RPC)](<https://devfeed.tech/topics/rpc.md>), [Kubernetes](<https://devfeed.tech/topics/kubernetes.md>)

Tags: [apiserver](<https://devfeed.tech/tags/apiserver.md>), [apply](<https://devfeed.tech/tags/apply.md>), [compaction](<https://devfeed.tech/tags/compaction.md>), [distributed](<https://devfeed.tech/tags/distributed.md>), [errcompacted](<https://devfeed.tech/tags/errcompacted.md>), [etcd](<https://devfeed.tech/tags/etcd.md>), [io](<https://devfeed.tech/tags/io.md>), [k8s](<https://devfeed.tech/tags/k8s.md>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [lag](<https://devfeed.tech/tags/lag.md>), [leader](<https://devfeed.tech/tags/leader.md>), [lease](<https://devfeed.tech/tags/lease.md>), [mvcc](<https://devfeed.tech/tags/mvcc.md>), [notify](<https://devfeed.tech/tags/notify.md>), [raft](<https://devfeed.tech/tags/raft.md>), [range](<https://devfeed.tech/tags/range.md>), [restore](<https://devfeed.tech/tags/restore.md>), [revision](<https://devfeed.tech/tags/revision.md>), [rpc](<https://devfeed.tech/tags/rpc.md>), [v3-5](<https://devfeed.tech/tags/v3-5.md>), [v3-5-33](<https://devfeed.tech/tags/v3-5-33.md>), [watch](<https://devfeed.tech/tags/watch.md>), [watchablestore](<https://devfeed.tech/tags/watchablestore.md>)

### AI overview

This article examines the etcd v3.5.33 watchableStore implementation, including synced and unsynced watcher groups, victims caused by backpressure, Apply-time notification, historical synchronization, and the ErrCompacted client resynchronization boundary. It also discusses event ordering, follower watch progress, and interactions with Kubernetes apiserver watch caches.

### Source excerpt

钉 etcd v3.5.33 watchableStore 的 synced/unsynced/victims 三分法、Apply 后 notify 与历史追赶 syncWatchersLoop，以及 CompactRevision 触发 ErrCompacted 时的客户端重同步边界。

## 【etcd】排障五轴：Raft/WAL/MVCC/Watch/Lease 口令表

DevFeed: [【etcd】排障五轴：Raft/WAL/MVCC/Watch/Lease 口令表](<https://devfeed.tech/articles/etcd-raft-wal-mvcc-watch-lease-33997.md>)

Original publisher: [Read original article](<https://quant67.com/post/etcd/15-troubleshoot/15-troubleshoot.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>), [Kubernetes](<https://devfeed.tech/topics/kubernetes.md>)

Tags: [apiserver](<https://devfeed.tech/tags/apiserver.md>), [applied-index](<https://devfeed.tech/tags/applied-index.md>), [apply](<https://devfeed.tech/tags/apply.md>), [committed-index](<https://devfeed.tech/tags/committed-index.md>), [compaction](<https://devfeed.tech/tags/compaction.md>), [distributed](<https://devfeed.tech/tags/distributed.md>), [errcompacted](<https://devfeed.tech/tags/errcompacted.md>), [etcd](<https://devfeed.tech/tags/etcd.md>), [five-axes](<https://devfeed.tech/tags/five-axes.md>), [incident](<https://devfeed.tech/tags/incident.md>), [keepalive](<https://devfeed.tech/tags/keepalive.md>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [lag](<https://devfeed.tech/tags/lag.md>), [lease](<https://devfeed.tech/tags/lease.md>), [mvcc](<https://devfeed.tech/tags/mvcc.md>), [node-lease](<https://devfeed.tech/tags/node-lease.md>), [raft](<https://devfeed.tech/tags/raft.md>), [restore](<https://devfeed.tech/tags/restore.md>), [troubleshooting](<https://devfeed.tech/tags/troubleshooting.md>), [ttl](<https://devfeed.tech/tags/ttl.md>), [v3](<https://devfeed.tech/tags/v3.md>), [v3-5](<https://devfeed.tech/tags/v3-5.md>), [v3-5-33](<https://devfeed.tech/tags/v3-5-33.md>), [wal](<https://devfeed.tech/tags/wal.md>), [watch](<https://devfeed.tech/tags/watch.md>)

### AI overview

This troubleshooting article organizes etcd failures into five diagnostic axes: Raft consensus, WAL persistence and recovery, MVCC storage and capacity, Watch client synchronization, and Lease TTL semantics. It maps symptoms to axes, explains relevant etcdctl health and status fields, and notes Kubernetes control-plane relationships, including apiserver and Node Lease behavior. The article is anchored to etcd v3.5.33.

### Source excerpt

按 Raft、WAL、MVCC、Watch、Lease 五轴做症状否证；解释 etcdctl endpoint status/health 字段语义；并对照 K8s 控制面 apiserver 超时与 Node Lease 漂移。

## 【etcd】Compaction、Defrag 与容量：quota、alarm 与 SLO

DevFeed: [【etcd】Compaction、Defrag 与容量：quota、alarm 与 SLO](<https://devfeed.tech/articles/etcd-compaction-defrag-quota-alarm-slo-33994.md>)

Original publisher: [Read original article](<https://quant67.com/post/etcd/12-compaction-quota/12-compaction-quota.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>), [Raft](<https://devfeed.tech/topics/raft.md>), [Kubernetes](<https://devfeed.tech/topics/kubernetes.md>)

Tags: [alarm](<https://devfeed.tech/tags/alarm.md>), [bbolt](<https://devfeed.tech/tags/bbolt.md>), [benchmark](<https://devfeed.tech/tags/benchmark.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>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [lag](<https://devfeed.tech/tags/lag.md>), [leader](<https://devfeed.tech/tags/leader.md>), [mvcc](<https://devfeed.tech/tags/mvcc.md>), [nospace](<https://devfeed.tech/tags/nospace.md>), [performance](<https://devfeed.tech/tags/performance.md>), [quota](<https://devfeed.tech/tags/quota.md>), [raft](<https://devfeed.tech/tags/raft.md>), [resourceversion](<https://devfeed.tech/tags/resourceversion.md>), [v3](<https://devfeed.tech/tags/v3.md>), [v3-5](<https://devfeed.tech/tags/v3-5.md>), [v3-5-33](<https://devfeed.tech/tags/v3-5-33.md>), [watch](<https://devfeed.tech/tags/watch.md>)

### AI overview

This technical article explains how etcd v3.5.33 compaction, defragmentation, quota handling, and the NOSPACE alarm interact. It distinguishes revision-history removal from bbolt file reclamation, describes periodic and revision-based auto-compaction, and connects retention, quota, defrag pauses, and Watch or Kubernetes control-plane behavior to operational SLOs.

### Source excerpt

钉 etcd v3.5.33 MVCC compaction 与 bbolt defrag 的分工、auto-compaction 保留窗口、quota-backend-bytes 与 NOSPACE alarm 写入门，以及 ErrCompacted 如何写进 Watch SLO。

## Waiting for PostgreSQL 19 - Add IGNORE NULLS/RESPECT NULLS option to Window functions.

DevFeed: [Waiting for PostgreSQL 19 - Add IGNORE NULLS/RESPECT NULLS option to Window functions.](<https://devfeed.tech/articles/waiting-for-postgresql-19-add-ignore-nulls-respect-nulls-option-to-window-functions-33665.md>)

Original publisher: [Read original article](<https://www.depesz.com/2025/10/13/waiting-for-postgresql-19-add-ignore-nulls-respect-nulls-option-to-window-functions/>)

Author: depesz

Published: 2025-10-13T11:13:52Z

Content type: article

Language: en

Sources: [select \* from depesz;](<https://devfeed.tech/sources/select-from-depesz.md>)

Topics: [PostgreSQL](<https://devfeed.tech/topics/postgresql.md>)

Tags: [first-value](<https://devfeed.tech/tags/first-value.md>), [functions](<https://devfeed.tech/tags/functions.md>), [ignore](<https://devfeed.tech/tags/ignore.md>), [lag](<https://devfeed.tech/tags/lag.md>), [last-value](<https://devfeed.tech/tags/last-value.md>), [lead](<https://devfeed.tech/tags/lead.md>), [nth-value](<https://devfeed.tech/tags/nth-value.md>), [null](<https://devfeed.tech/tags/null.md>), [nulls](<https://devfeed.tech/tags/nulls.md>), [pg19](<https://devfeed.tech/tags/pg19.md>), [postgresql](<https://devfeed.tech/tags/postgresql.md>), [uncategorized](<https://devfeed.tech/tags/uncategorized.md>), [waiting](<https://devfeed.tech/tags/waiting.md>), [window](<https://devfeed.tech/tags/window.md>), [window-functions](<https://devfeed.tech/tags/window-functions.md>)

### AI overview

The article describes a PostgreSQL patch adding IGNORE NULLS and RESPECT NULLS options, also called a null treatment clause, to the lead, lag, first_value, last_value, and nth_value window functions. IGNORE NULLS skips NULL values, while RESPECT NULLS remains the default behavior.

### Source excerpt

On 3rd of October 2025, Tatsuo Ishii committed patch: Add IGNORE NULLS/RESPECT NULLS option to Window functions. Add IGNORE NULLS/RESPECT NULLS option (null treatment clause) to lead, lag, first_value, last_value and nth_value window functions. If unspecified, the default is RESPECT NULLS which includes NULL values in any result calculation. IGNORE NULLS ignores NULL values. ... Continue reading "Waiting for PostgreSQL 19 - Add IGNORE NULLS/RESPECT NULLS option to Window functions."

## 4K display on MacOS: the saga

DevFeed: [4K display on MacOS: the saga](<https://devfeed.tech/articles/4k-display-on-macos-the-saga-37806.md>)

Original publisher: [Read original article](<https://carlosbecker.com/posts/macos-4k-display/>)

Author: Carlos Alexandro Becker

Published: 2020-02-05T00:00:00Z

Content type: opinion

Language: en

Sources: [Carlos Becker](<https://devfeed.tech/sources/carlos-becker.md>)

Topics: [macOS](<https://devfeed.tech/topics/macos.md>), [hdmi](<https://devfeed.tech/topics/hdmi.md>), [Bluetooth](<https://devfeed.tech/topics/bluetooth.md>), [dell](<https://devfeed.tech/topics/dell.md>)

Tags: [4k](<https://devfeed.tech/tags/4k.md>), [adapter](<https://devfeed.tech/tags/adapter.md>), [apple](<https://devfeed.tech/tags/apple.md>), [bluetooth](<https://devfeed.tech/tags/bluetooth.md>), [display](<https://devfeed.tech/tags/display.md>), [electronics](<https://devfeed.tech/tags/electronics.md>), [hdmi](<https://devfeed.tech/tags/hdmi.md>), [lag](<https://devfeed.tech/tags/lag.md>), [mac](<https://devfeed.tech/tags/mac.md>), [macos](<https://devfeed.tech/tags/macos.md>), [pretty](<https://devfeed.tech/tags/pretty.md>), [solved](<https://devfeed.tech/tags/solved.md>)

### AI overview

A personal account of configuring a Dell U2718Q 4K display with a MacBook Pro. The initial USB-C-to-HDMI setup produced 4K resolution at 30 Hz, while a USB-C-to-miniDisplayPort cable resolved the display problems described.

### Source excerpt

I recently got a 4K display, and it didn't work as I expected on my MacBook Pro. This is what I tried, what worked and what didn't.

## Talking at the SFPUG

DevFeed: [Talking at the SFPUG](<https://devfeed.tech/articles/talking-at-the-sfpug-34511.md>)

Original publisher: [Read original article](<https://tapoueh.org/blog/2013/07/talking-at-the-sfpug/>)

Author: Dimitri Fontaine PostgreSQL Major Contributor; Author

Published: 2013-07-19T08:24:00Z

Content type: opinion

Language: en

Sources: [Dimitri Fontaine](<https://devfeed.tech/sources/dimitri-fontaine.md>)

Topics: [Tool](<https://devfeed.tech/topics/tool.md>), [Documentation](<https://devfeed.tech/topics/documentation.md>), [version](<https://devfeed.tech/topics/version.md>), [upgrade](<https://devfeed.tech/topics/upgrade.md>)

Tags: [batch](<https://devfeed.tech/tags/batch.md>), [lag](<https://devfeed.tech/tags/lag.md>), [technical](<https://devfeed.tech/tags/technical.md>), [technical-writing](<https://devfeed.tech/tags/technical-writing.md>), [tools](<https://devfeed.tech/tags/tools.md>), [upgrade](<https://devfeed.tech/tags/upgrade.md>), [version](<https://devfeed.tech/tags/version.md>)

### AI overview

The author recounts speaking at an SFPUG meeting in San Francisco about the latest version of Skytools. The talk highlighted missing documentation and prompted questions about upgrades, PGQ, Londiste operations, batch size, and lag. Bazaarvoice's use of Skytools contributed to its interest in the discussion.

### Source excerpt

Those days feel really lucky to me. I'm currently visiting friends and customers in San Francisco, and really enjoying my trip here! Of course Josh Berkus took the opportunity to organise a SFPUG meeting and I had the pleasure of being the speaker over there. My talk was about the most recent version of Skytools and the opportunity to realise that we're still missing a lot on documentation. One of the attendee did propose to help us on that front as he apparently really likes technical writing. I hope that effort will happen and help solve the main issue here.