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Production CRUD in Java Without the Framework Tax
A practical walkthrough of SQL-First persistence: no XML, no Mapper interfaces, no generated queries. I maintain a Java backend that handles ~1M requests/day. For persistence, we used to run MyBatis. The XML was manageable at first, then it wasn't. Dynamic conditions became <if> tag soup. A simple join query needed three files and two languages. We switched to a simpler approach. Here's how it works for the most common case: single-table CRUD. What You Need Java 21+ Spring Boot (any 3.x) A database (H2 for the demo, MySQL/PostgreSQL for production) That's it. No XML parser, no code generator, no annotation processor. The Project pom.xml src/main/java/example/ DemoApplication.java user/ User.java -- entity UserDao.java -- data access UserCond.java -- query conditions src/main/resources/ application.yml schema.sql Three Java files for a complete CRUD API. The Entity @Data @Builder @Table ( "sys_user" ) public class User { @Id private Long id ; private String name ; private Integer age ; private String email ; // ... other fields // These four are auto-managed: private LocalDateTime createTime ; private Long createBy ; private LocalDateTime updateTime ; private Long updateBy ; private Byte dr ; // 0 = active, 1 = soft-deleted } @Table maps to the database table. @Id marks the primary key (Snowflake ID by default). The audit fields and soft-delete marker are handled automatically—you don't set them in business code. The DAO @Repository public class UserDao extends BaseDao < User > { // Empty. All CRUD methods inherited. } BaseDao provides save , saveBatch , update , delete , findById , list , page , count , exists . For single-table operations, this is all you need. The Conditions @Getter @Setter @Builder public class UserCond extends BaseCondition { private String name ; private Integer ageMin ; private Integer ageMax ; private Byte dr ; private Object [] ids ; @Override protected void addCondition () { and ( "name LIKE" , name , 3 ); // 3 = %value% and ( "age >=" , ag
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PostgreSQL 22036 Error: Causes and Solutions Complete Guide
PostgreSQL Error 22036: non numeric sql json item PostgreSQL error code 22036 ( non numeric sql json item ) occurs when a SQL/JSON path expression attempts to perform a numeric operation on a JSON item that is not a number — such as a string, boolean, array, or object. This error was introduced alongside the SQL/JSON Path feature in PostgreSQL 12 and typically surfaces in queries using jsonb_path_query , jsonb_path_exists , or the @@ and @? operators. Top 3 Causes 1. Numeric Values Stored as Strings The most common cause is JSON data where numbers are stored as quoted strings (e.g., "price": "100" instead of "price": 100 ). This frequently happens with data from external APIs or legacy systems that don't enforce type consistency. -- Triggers 22036: "price" is a string, not a number SELECT jsonb_path_query ( '{"price": "100"}' , '$.price + 50' ); -- ERROR: non numeric SQL/JSON item -- Fix: Use the .double() conversion method in JSON Path SELECT jsonb_path_query ( '{"price": "100"}' , '$.price.double() + 50' ); -- Result: 150 -- Alternative fix: Cast at the SQL level SELECT ( data ->> 'price' ):: numeric + 50 FROM ( SELECT '{"price": "100"}' :: jsonb AS data ) t ; -- Result: 150 2. Arithmetic Applied Directly to Arrays or Objects Developers sometimes write JSON Path expressions that target an entire array or object instead of individual elements, then attempt arithmetic on the result. -- Triggers 22036: $.scores returns an array, not a number SELECT jsonb_path_query ( '{"scores": [80, 90, 70]}' , '$.scores + 10' ); -- ERROR: non numeric SQL/JSON item -- Fix: Target a specific array index SELECT jsonb_path_query ( '{"scores": [80, 90, 70]}' , '$.scores[0] + 10' ); -- Result: 90 -- Fix: Use wildcard to apply operation to each element SELECT jsonb_path_query ( '{"scores": [80, 90, 70]}' , '$.scores[*] + 10' ); -- Results: 90, 100, 80 -- Fix: Use unnest for aggregation use cases SELECT elem :: numeric + 10 FROM jsonb_array_elements ( '{"scores": [80, 90, 70]}' :: jsonb ->
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A model with R-squared near 0 can still give valid 90% prediction intervals - here's why (and the catch)
I recently calibrated a recovery-rate model that had only two weak features. Its point accuracy was almost nothing — R² basically zero. I expected its uncertainty estimates to be junk too. They weren't: the 90% conformal prediction intervals covered ~89% of held-out outcomes. Valid, just wide . That surprised me enough to nail it down, because it contradicts a belief a lot of us carry around: "my model isn't accurate, so I can't trust its uncertainty." For split conformal prediction, that's backwards. Here's the precise statement, a runnable demo, and the one caveat that actually bites. Coverage is a property of the procedure, not the model Split conformal prediction gives a distribution-free, finite-sample marginal coverage guarantee : P( Y ∈ Ĉ(X) ) ≥ 1 − α and it holds for any point model, as long as the calibration and test data are exchangeable. The model is a black box. You fit it however you like, then on a held-out calibration set you take the (1−α) quantile of the absolute residuals, and that quantile becomes the half-width of your intervals. Nowhere does that construction require the model to be good. A bad model just has large residuals, so the calibration quantile is large, so the intervals are wide — wide enough to still cover at the stated rate. Accuracy doesn't buy you validity ; it buys you efficiency (narrower intervals at the same coverage). The demo (numbers are reproducible, seed fixed) Same dataset and target, three models from strong to useless, target coverage 90%: model R² marginal coverage mean interval width gradient boosting 0.741 0.895 5.39 weak linear (1 noisy feature) 0.061 0.905 10.39 predict-the-mean −0.000 0.907 10.83 All three land at ~90% coverage. The only thing that changes is width: the good model's intervals are half as wide . That's the whole story in one table — validity is constant, efficiency tracks accuracy. import numpy as np from sklearn.linear_model import LinearRegression from sklearn.ensemble import GradientBoostingReg
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Cybercriminals allegedly hacked tens of thousands of Fortinet firewalls used by major companies all over the world
An alleged Russian-speaking group of cybercriminals is reportedly compromising and targeting several major companies that use Fortinet Firewalls and VPNs through previously known passwords.
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Vector Search in Elasticsearch: From Keywords to Meaning - Building Semantic Search and RAG Pipelines
You type "k8s deployment troubleshooting" into your documentation search. The top result is a page about Kubernetes architecture that never mentions the word "troubleshooting." It is exactly what you need. BM25 would have missed it entirely. This is the promise of vector search: finding documents by meaning, not just matching words. In 2025 and 2026, vector search has moved from niche ML engineering to a core Elasticsearch capability. If you are building search for AI applications - RAG pipelines, semantic Q&A, recommendation systems - understanding how Elasticsearch handles vectors is no longer optional. I have spent the past year building RAG pipelines at Cloudera, and I have learned that vector search is powerful but easy to misuse. This post covers what works, what does not, and how to implement it in production. Why Vector Search Matters (And When It Does Not) BM25, which we covered in a previous post, is brilliant at matching exact terms. But it is fundamentally lexical. It does not understand that: "k8s" and "kubernetes" are the same thing "docker container" and "containerization" are related concepts "out of memory error" and "heap exhaustion" describe the same problem Vector search solves this by converting text into high-dimensional numerical vectors (embeddings) where semantically similar content lives close together in vector space. A query for "k8s deployment troubleshooting" gets embedded into a vector, and Elasticsearch finds the nearest document vectors - even if they do not share a single keyword. But vector search is not a replacement for BM25. It is a complement. BM25 is faster, requires no ML infrastructure, and excels at exact-term matching. Vector search is slower, requires embedding models, and shines at conceptual similarity. The best search systems in 2026 use both. How Elasticsearch Stores and Indexes Vectors Elasticsearch introduced the dense_vector field type in version 7.x and has dramatically improved it through 8.x and into 2026. Here
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How to Rewrite a Chinese-Tenured Faculty Role for US Data Scientist Jobs
Why Your Chinese-Tenured Faculty Resume Won’t Work in US Industry US data scientist hiring managers scan a resume in 7–15 seconds looking for one thing: evidence you can solve business problems with data. A Chinese faculty resume often leads with tenure status, publication counts, and grant amounts—none of which translate to industry value. Worse, the CV-style length and Chinese-specific qualifications (e.g., “Professor of Record,” “National Natural Science Foundation PI”) confuse HR software and recruiters unfamiliar with that system. You need to strip the academic frame and rebuild around what a US data scientist does: clean messy data, build predictive models, deploy to production, and communicate results to non-technical stakeholders. Think of every faculty achievement as raw material you must reframe. Core Rewriting Rules: From Academic to Industry Rule 1: Replace Tenure Rank with a US-Equivalent Data Science Title Do not list “Tenured Associate Professor” unless it is your most recent position at a well-known university (e.g., Peking University, Tsinghua). Instead, use a title that reveals your function: “Senior Data Scientist – Research Computing” or “Lead Data Scientist – Machine Learning Research Lab.” The point is to signal the job function, not the academic rank. Example: Before: “Tenured Associate Professor, School of Computer Science, Fudan University” After: “Senior Data Scientist / Research Lead, Fudan University AI Lab” Rule 2: Translate Every Accomplishment into a Business-Relevant Metric Chinese faculty resumes often say “published 15 papers in top-tier journals” or “secured ¥3M in research funding.” That means nothing to a hiring manager at a fintech startup. Instead, describe what you did with the data and the outcome. Concrete example – before and after: BEFORE (faculty bullet): “Led research project on deep learning for medical image segmentation; published 3 papers in IEEE TMI.” AFTER (industry data scientist bullet): “Built and validated a co
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UUID v4 vs UUID v7: Performance, Security and Real Benchmarks at 100M
TL;DR — UUID v7 trie 13× plus vite que v4 en simulation B-tree (1M entrées), expose une empreinte mémoire identique, mais révèle son timestamp d'émission. UUID v4 reste le choix "zéro réflexion" pour les identifiants isolés. Le reste de cet article vous donnera les données pour décider. Introduction Les UUIDs sont omniprésents dans les systèmes modernes : clés primaires de bases de données, identifiants de sessions, tokens de traçabilité. Pourtant, le choix de la version impacte directement les performances en écriture et en lecture, la fragmentation des index, et — dans certains contextes — la confidentialité des données. UUID v4 (RFC 4122, 2005) est aujourd'hui la version par défaut de presque tous les ORM et frameworks. UUID v7 (RFC 9562, 2024) est son successeur moderne, conçu pour corriger son principal défaut : le désordre lexicographique. Dans cet article, nous allons mettre les deux en face avec des benchmarks réels sur des volumes de 100 000 à 10 millions d'UUIDs , analyser leur structure bit par bit, et vous donner une grille de décision claire. Structure interne : ce que contiennent ces 128 bits UUID v4 xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx Bits Contenu 0–47 Aléatoire 48–51 Version (0100 = 4) 52–63 Aléatoire 64–65 Variant (10) 66–127 Aléatoire 122 bits d'entropie pure. Aucune information temporelle. Chaque UUID est statistiquement indépendant des autres. UUID v7 019ed5c8-2a2f-7974-91f2-6ba1f313dcfa └──────────────┘ 48 bits = timestamp Unix en millisecondes Bits Contenu 0–47 Timestamp Unix (ms) 48–51 Version (0111 = 7) 52–63 Aléatoire (sub-ms ou compteur) 64–65 Variant (10) 66–127 Aléatoire 74 bits d'entropie + 48 bits de temps. Naturellement monotone : deux UUIDs générés dans la même milliseconde sont toujours distincts et ordonnés de façon cohérente. Lecture du timestamp (Python) : import uuid6 u = uuid6 . uuid7 () b = u . bytes ts_ms = int . from_bytes ( b [: 6 ], ' big ' ) # → 1781703125553 (ms depuis epoch Unix) Depuis la sortie de nos benchmarks : [00
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Presentation: From Hype to Strong Foundations: What the Rise, Fall and Resurgence of Agents Can Teach Us About Outlasting the Cycle
Aditya Kumarakrishnan explains how to move past the "amnesia phase" of AI. He shares a blueprint for engineering leaders to build modular agent frameworks using CoALA, leverage decades of process science for scalable workflows, and "terraform" legacy environments into robust, event-sourced artifacts capable of handling unpredictable, cross-functional agent demands. By Aditya Kumarakrishnan
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GitHub Copilot Desktop App Targets Parallel Agentic Workflows
GitHub has introduced the GitHub Copilot app, a desktop control centre for agent-native development that aims to keep engineers in charge while AI agents handle more coding work. Mario Rodriguez writes on the GitHub blog that the recent wave of coding agents has brought faster delivery but also "disjointed workflows, more context switching, and too much time spent reviewing agent-generated code". By Matt Saunders
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Day 21 : Time-Series Data in ClickHouse®
Time-series data is one of the most common types of data generated by modern applications. Every log entry, API request, metric, transaction, sensor reading, or user interaction is recorded with a timestamp, making time the primary dimension for analysis. As organizations collect billions of these records, efficiently storing and querying them becomes increasingly challenging. This is where ClickHouse® excels. Although ClickHouse is not a dedicated time-series database, its columnar storage architecture, vectorized query execution, high compression ratios, and massively parallel processing make it an excellent choice for time-series analytics at scale. It is capable of ingesting large volumes of data while delivering analytical queries in milliseconds. The article begins by explaining the fundamentals of time-series data and highlighting common real-world use cases such as application monitoring, IoT sensor data, financial market analysis, server metrics, user activity tracking, and business analytics. These workloads typically involve continuous data ingestion, time-based filtering, aggregations, and trend analysis. One of ClickHouse's biggest strengths is its optimization for analytical workloads. Since data is stored column-wise rather than row-wise, only the required columns are read during query execution. Combined with compression and vectorized processing, this significantly reduces I/O and improves query performance over massive datasets. The article also demonstrates how to create an optimized table for time-series workloads using the MergeTree engine. Proper partitioning by month and ordering data by dimensions and timestamps help ClickHouse prune unnecessary partitions and efficiently locate relevant data during queries. Several practical SQL examples are covered, including: Filtering records within a specific time range Aggregating metrics by hour, day, week, or month Calculating averages, sums, minimums, and maximums Grouping events over time Working wi
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Why AI Agents Make Me Reach for SQLite
Lately I keep reaching for SQLite where, before, I'd have reached for Postgres without thinking. It started with small services, then a bigger question: could a multi-tenant SaaS actually run on SQLite? And for AI agents specifically, isn't a local, embedded database the more natural home for their state? Turso is the version of this stack I've found most compelling so far, especially when paired with Cloudflare. I wish D1 would reach embedded-replica parity with Turso, and that AWS offered a managed SQLite-style service the way it offers RDS for Postgres. This isn't a "Postgres is over" argument. I still use Postgres more often than SQLite. And it isn't advice. It's just where my thinking has drifted recently — written down mostly so I can find out where it's wrong. Read it as one person's notes, not a recommendation. Where I've landed for now (and expect to keep revising): SQLite isn't replacing Postgres. For work state , it's increasingly my first reach, not my last. AI agents push this harder: their state is high-churn, local, and mostly private. The answer isn't all-local. It's a local workbench plus a central ledger . Why the old default existed For years, "where does the data live?" had one practical answer: a server, behind an API, in a shared Postgres. A lot of that wasn't architecture — it was the cheapest shape available. SQLite was already everywhere, but it lacked the operational layer that makes a database viable as SaaS infrastructure: networking, replication, managed backups, and a way to run many small databases without drowning in tooling. So centralizing was the path of least resistance, and a tenant_id column in shared Postgres became the reflex. What changed isn't SQLite. It's that the ecosystem grew the missing parts — and for a growing class of workloads, the thing doing the most frequent writing moved onto my own machine. The constraint that's lifting SQLite itself is, by design: Embedded, not networked — a library, nothing listens on a port.
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Discovering PII Inside InterSystems IRIS
Data privacy regulations such as GDPR, LGPD, and HIPAA demand that organizations know exactly where Personally Identifiable Information (PII) lives inside their databases. Yet in practice, most teams rely on manual inventories, tribal knowledge, or external scanning tools that require data to leave the database engine — a process that itself creates privacy and security risks. This article presents an MVP that takes a different approach: it runs PII detection inside InterSystems IRIS using Embedded Python, analyzing data where it lives and never exporting it to an external process. The result is a lightweight, non-intrusive utility that scans your tables, identifies PII using AI, and produces a structured CSV report — all without data ever leaving the IRIS process. The Problem: PII You Don't Know You Have Organizations today face a painful blind spot. A typical IRIS instance may contain hundreds of tables across dozens of schemas, some holding decades of accumulated data. Columns named ContactInfo , Notes , or Description might silently contain social security numbers, email addresses, or government IDs — sometimes intentionally, sometimes as a side effect of free-text fields that capture whatever users type in. Traditional approaches to PII discovery share a common flaw: they require data extraction. You export samples, send them to an external service, or pipe them through a standalone tool. Every step in that pipeline is an additional attack surface and a potential compliance violation. The principle of data sovereignty — keeping data within its jurisdiction and under controlled access — suggests a better path: bring the analysis to the data, not the data to the analysis. This is not just a technical preference; it is a governance requirement: GDPR (EU) — Article 28 requires that any processing of personal data by a third-party processor be governed by a binding contract covering subject-matter, duration, purpose, data types, and obligations [ Art. 28 GDPR ]. Art
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DOJ claims xAI’s unpermitted gas turbines are a matter of ‘national, economic, and energy security’
The Justice department says the Pentagon needs xAI to keep using its unpermitted gas turbines.
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I cleaned India's Census 2011 data so you never have to
Every Indian data scientist hits the same wall. You need district-level population data. You go to censusindia.gov.in. You find hundreds of inconsistent Excel files with merged headers, footnote rows, and zero documentation. You spend a full day just loading the data before doing any actual analysis. I fixed that. Once. For everyone. What I built indiaset/census-2011 India's Census 2011 district data, clean, typed, and ready for pandas. 640 districts · 29 columns · 0 missing values Validated against official India total · LGD codes attached Load it in 4 lines from huggingface_hub import hf_hub_download import pandas as pd path = hf_hub_download ( repo_id = " indiaset/census-2011 " , filename = " census_2011_districts_final.parquet " , repo_type = " dataset " ) df = pd . read_parquet ( path ) print ( df . shape ) # (640, 29) What's in it Column Description state_code Census 2011 state code state_name Official state/UT name district_code Census 2011 district code district_name District name as per Census lgd_code LGD permanent district code district_name_lgd District name as per LGD pop_total Total population pop_male Male population pop_female Female population pop_under6_total Children under 6 years pop_sc Scheduled Caste population pop_st Scheduled Tribe population literate_total Literate persons literate_male Literate males literate_female Literate females illiterate_total Illiterate persons workers_total Total workers workers_male Male workers workers_female Female workers non_workers_total Non workers literacy_rate Literate / Total × 100 sex_ratio Females per 1000 males workforce_participation Workers / Total × 100 The validation The most important test - do all 640 district populations sum to India's official total? print ( df [ ' pop_total ' ]. sum ()) # 1210854977 ✅ — exact match, zero discrepancy What the data actually shows Most literate district → Pathanamthitta, Kerala : 88.74% Least literate district → Alirajpur, Madhya Pradesh : 28.77% Literacy gap acro
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PostgreSQL 19 Beta Introduces SQL Graph Queries and Concurrent Table Repacking
PostgreSQL 19 Beta has been announced, with general availability expected in September, following the project's yearly major-release cadence. This release introduces native SQL Property Graph Queries (SQL/PGQ), concurrent table repacking to reclaim storage without downtime, and a broad set of performance, observability, and administration improvements. By Renato Losio
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I Built a Mini Message Broker in Pure Python and Finally Understood How Kafka Moves Millions of Events
Last year I was on a team that pushed 40 million events per day through Kafka. We had consumer lag alerts, rebalancing incidents, and a whole runbook for when the broker got behind. I understood how to operate Kafka. But I did not understand how Kafka works. So I built a tiny one. No dependencies. No Zookeeper. No JVM. Just Python and the core ideas. Here is what I learned. The Three Things Kafka Actually Does People say "Kafka is a message queue." That is not quite right. Kafka is a distributed commit log . It has three jobs: Accept writes from producers and append them to a log Let consumers read from any offset in that log Remember where each consumer group is up to That third one is the thing that makes Kafka different from a traditional queue. A queue forgets a message once it is consumed. Kafka remembers. You can replay. You can have 10 different consumer groups reading the same topic at different speeds. The code to implement this is smaller than you think. brokelite: A Message Broker in 120 Lines import threading import time from collections import defaultdict from typing import Dict , List , Tuple class Partition : """ Append-only log for one partition of a topic. """ def __init__ ( self ): self . _log : List [ Tuple [ int , bytes ]] = [] # (offset, message) self . _lock = threading . Lock () self . _next_offset = 0 def append ( self , message : bytes ) -> int : with self . _lock : offset = self . _next_offset self . _log . append (( offset , message )) self . _next_offset += 1 return offset def read_from ( self , offset : int , max_count : int = 100 ) -> List [ Tuple [ int , bytes ]]: with self . _lock : return [ ( off , msg ) for off , msg in self . _log if off >= offset ][: max_count ] def __len__ ( self ): return self . _next_offset class Topic : """ A topic is just N partitions. """ def __init__ ( self , name : str , num_partitions : int = 3 ): self . name = name self . partitions = [ Partition () for _ in range ( num_partitions )] def route ( self , k
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CloudNativePG: Running PostgreSQL in Kubernetes Without the Pain
A CloudNativePG cluster that sits in Setting up primary forever, with zero error events on the Cluster resource and a perfectly healthy operator, is one of the more frustrating ways to spend an afternoon. The operator says it's working. The pods never appear. And the actual cause has nothing to do with the database at all. Running stateful databases on Kubernetes used to be the thing everyone told you not to do. CloudNativePG (CNPG) changed that calculus for a lot of people, including me. It's a proper operator: it handles failover, backups, connection routing, and rolling upgrades through native Kubernetes primitives instead of bolting Postgres onto a StatefulSet and praying. If you run a hardened cluster with admission controllers, network policies, and least-privilege RBAC, this post is about the friction you'll hit that the quickstart never mentions. Who should care If your cluster is vanilla, kubectl apply the operator and a Cluster manifest, and you're done in ten minutes. The CNPG docs are genuinely good for that path. This is for the rest of us: people running Kyverno or OPA Gatekeeper, self-signed cert chains, and the kind of policy-as-code setup where every workload has to justify its existence. That's where CNPG stops being a ten-minute install and starts being an integration project. What I tried first The first instinct, when a CNPG cluster hangs, is to assume you got the database config wrong. So you go read your Cluster manifest line by line. You check the storage class. You check that the PVC bound. You bump the operator log level and watch it cheerfully report that it's reconciling, over and over, with no complaints. Here's the trap: the CNPG operator doesn't run initdb itself. It creates a Kubernetes Job to bootstrap the primary. That Job spawns a Pod. And in a hardened cluster, the Pod is where everything dies, because your admission controller is judging it against policies the operator's own Pods were exempted from but the bootstrap Job was not.
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PostgreSQL HA Risks, Replication Internals, & Rapid Branching
PostgreSQL HA Risks, Replication Internals, & Rapid Branching Today's Highlights Today's highlights include critical insights into Patroni's replication slot management, an architectural deep dive into PostgreSQL's synchronous commit behavior, and a look at achieving sub-second database branching for enhanced developer workflows. When Patroni Silently Deletes Your Replication Slots (Planet PostgreSQL) Source: https://postgr.es/p/9lM This article uncovers a critical operational pitfall when using Patroni, a popular high-availability solution for PostgreSQL, with logical replication. It details how Patroni, under specific failure scenarios or configuration changes, can silently remove replication slots without warning. Replication slots are vital for ensuring that standbys or logical replication consumers do not miss any changes, making their deletion a potentially severe data integrity issue. The author explains the underlying reasons for this behavior, often related to how Patroni manages pg_basebackup or restores, and how it might not re-create logical replication slots automatically. The post provides concrete scenarios where this can occur, such as when a new primary is elected and old slots aren't re-established, or during certain recovery operations. It emphasizes the importance of diligent monitoring of replication slot status and proposes strategies to mitigate the risk of silent deletion, including careful Patroni configuration and robust alerting mechanisms. This insight is crucial for database administrators and developers relying on Patroni for resilient PostgreSQL deployments, highlighting a subtle but dangerous interaction between these two powerful components. Comment: This is a must-read for anyone running Patroni with PostgreSQL, especially if using logical replication. Understanding this specific behavior of Patroni deleting replication slots silently is essential to prevent unexpected data loss or integrity issues in production. Why Postgres Doesn'
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Anthropic Explains How Claude Builds Its Own Execution Harnesses
Anthropic has published additional details about the orchestration system behind Claude Code's recently introduced Dynamic Workflows, highlighting how the feature generates custom execution harnesses designed to coordinate teams of AI agents for complex tasks. By Robert Krzaczyński
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Your Hand-Rolled Two-Phase Commit Between Two Databases Isn't Atomic
I had a write that spanned two physically separate databases. A rename that had to propagate across several tables in one database and a couple of tables in another, and the two had to stay consistent. No distributed transaction coordinator was available to me. So I did the obvious thing: opened a transaction on each, did the work, and committed them one after the other inside a try/catch with rollbacks on both sides. It felt safe. It compiled. It passed tests. Then I drew the failure on a whiteboard, and the safety evaporated. The window that ruins everything Here's the structure, simplified: await using var txA = await dbA . Database . BeginTransactionAsync (); await using var txB = await dbB . Database . BeginTransactionAsync (); await DoWorkOnA ( dbA ); await DoWorkOnB ( dbB ); await txA . CommitAsync (); // <-- succeeds await txB . CommitAsync (); // <-- what if this throws? Two transactions do not make one atomic operation. CommitAsync is a point of no return, and there are two of them. Between the first commit returning and the second one starting, there is a window. If txB fails in that window — the connection drops, the process is killed, the database hiccups — then A is permanently committed and B never happens. Your rollback in the catch block is useless: you can't roll back txA , it's already durable. The two databases now disagree, and nothing in your code will heal that on its own. This is the dual-write problem , and it's not a bug you can fix by being more careful with try/catch. The atomicity you want simply isn't available from two independent commits. Ordering them, nesting them, wrapping them — none of it closes the window, because the window is inherent to having two commit points. Why "it's never failed" isn't reassurance The seductive thing about this pattern is that the window is small, so in practice it almost never triggers. You can run it for a year and never see an inconsistency. That's exactly what makes it dangerous: it trains you to tr