Simon Willison’s Weblog

Items tagged databases, mysql

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github/gh-ost: Thoughts on Foreign Keys? The biggest challenge I’ve seen with foreign key constraints at scale (at least with MySQL) is how they conflict with online schema migrations using tools like pt-online-schema-change or GitHub’s gh-ost. This is a good explanation of the issue by Shlomi Noach, one of the gh-ost maintainers. # 19th June 2018, 4:12 pm

Showdown: MySQL 8 vs PostgreSQL 10 (via) MySQL 8 makes comparisons between PostgreSQL and MySQL far more interesting, as it closes some of the key feature gaps. Meanwhile the PostgreSQL replication story (long one of MySQL’s key advantages) has improved dramatically in recent versions. This article offers a useful overview of the current differences, including diving into some of the less obvious implementation details that differ between the two. # 23rd May 2018, 5:02 pm

What are the key insights in mastering SQL queries?

You may find this article useful (despite the list-o-matic name): 10 Easy Steps to a Complete Understanding of SQL—I’ve been using SQL for years but I found that some of the concepts explained there helped firm up my fundamental understanding of how to use it effectively.

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How was FriendFeed’s schema less db faster than pure MySQL?

The principle reason they switched to a schemaless DB was to work around the challenges of having to make schemes changes in MySQL, which can lock the table and take hours if bit days to complete in large tables.

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Should I store markdown instead of HTML into database fields?

You should store the exact format that was entered by the user.

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What tools and techniques are used for relational database version control (structure and data)?

The term you are looking for is database migrations (sometimes called database change scripts).

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What are XML feed best practices?

It sounds like you’re pretty much screwed already, if you’re dealing with companies that still think FTPing XML around is a sensible thing to do.

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Is a relational database with many-to-many relationships difficult to develop into a web app?

Many to Many tables can be a bit of a pain to deal with using regular SQL, but a good ORM can abstract away any potential complexity almost entirely. I find using the Django ORM means I’m much less likely to shy away from a design that involves a many-to-many relationship because I know it won’t increase the complexity of the application. I imagine the Rails ORM has the same effect.

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MySQL Connector/Python. A pure Python implementation of the MySQL client/server protocol, meaning you can talk to a MySQL server from Python without needing to first install the MySQL client libraries (which often requires compiling from source). # 2nd October 2009, 2:16 pm

Why we migrated from MySQL to MongoDB. Includes some useful information on MongoDB’s limitations—for example, running many different collections can waste disk space and repairing large datasets or bulk deleting many rows can block and lock the database for the duration of the operation. # 27th July 2009, 10:49 am

Introducing Digg’s IDDB Infrastructure. IDDB is Digg’s new infrastructure component for sharding data across multiple databases, with support for both MySQL and memcachedb. “The DiggBar and URL minifying service is powered by a 16 machine IDDB cluster, which includes 8 write masters in the index and 8 MySQL storage nodes.” # 3rd April 2009, 8:42 pm

[Drizzle] won’t be a get-out-of-jail-free card for very write-heavy applications but I bet it will do wonders for heavily replicated, heavily federated, read-heavy architectures (you know, normal stuff).

Richard Crowley # 8th March 2009, 6:05 pm

Database Sharding at Netlog, with MySQL and PHP. Detailed MySQL sharding case study from Netlog, who serve five billion page requests a month using thousands of shards across more than 80 database servers. # 2nd March 2009, 10:22 am

How FriendFeed uses MySQL to store schema-less data. The pain of altering/ adding indexes to tables with 250 million rows was killing their ability to try out new features, so they’ve moved to storing pickled Python objects and manually creating the indexes they need as denormalised two column tables. These can be created and dropped much more easily, and are continually populated by an off-line index building process. # 27th February 2009, 2:33 pm

Spock Proxy. A MySQL Proxy fork (no Lua) that concentrates solely on sharding, by parsing incoming SQL statements and redirecting them across multiple databases. There are some limitations on the SQL that can be handled (no nested queries, joins across a maximum of two tables) but generally it looks pretty impressive. # 11th December 2008, 9:49 am

Drizzle, Clouds, “What If?”. Exciting news in the world of MySQL: Drizzle is a new project to produce a massively stripped down version of the database server—InnoDB/UTF8 only, no permissions, views, stored procedures or triggers, simplified field types, optimised for the common subset of functionality used by web apps. MySQL’s Firefox? # 23rd July 2008, 12:30 am

Sun To Acquire MySQL. Sun also employ Josh Berkus, one of the lead developers of PostgreSQL. # 16th January 2008, 1:55 pm

CouchDB: Thinking beyond the RDBMS. CouchDB is a fascinating project—an Erlang powered non-relational database with a JSON API that lets you define “views” (really computed tables) based on JavaScript functions that execute using map/reduce. Damien Katz, the main developer currently works for MySQL and used to work on Lotus Notes. # 3rd September 2007, 9:48 am