151 articles · 35 databases · 63 topics
Practical tutorials, performance tuning and internals for SQL Server, PostgreSQL, MySQL, MongoDB, Redis and every engine in between — written by people who run them in production.
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RelationalMicrosoft's enterprise relational database engine.
34 articles →
RelationalThe world's most advanced open-source relational database.
17 articles →
RelationalThe popular open-source database behind much of the web.
11 articles →
RelationalThe long-standing heavyweight of enterprise data.
9 articles →
EmbeddedA tiny, serverless SQL engine inside everything.
8 articles →
DocumentA document database built around flexible JSON-like documents.
12 articles →
Key-valueIn-memory data structures at microsecond speed.
7 articles →
Wide-columnMasterless, linearly scalable wide-column store.
3 articles →
Editor's picks
GeneralBeginner0.1 isn't exact in binary, so sums drift and cents go missing. Use DECIMAL or integer minor units, store the currency, and make rounding an explicit business rule.
In this article
· 6 min read
PostgreSQLBeginnerAfter an import or migration, every insert collides with an existing id because the sequence is behind. Reset one or all sequences, and prevent it with identity columns.
#data-types#migrations#troubleshooting
Neo4jBeginnerMERGE creates the whole pattern if any part is missing, and it can't stop concurrent duplicates without a constraint. How to merge correctly and clean up existing duplicates.
#concurrency#data-modeling#troubleshooting
Fresh commits
ElasticsearchIntermediateDynamic mapping made your field text, so term queries miss, and mappings can't be changed in place. Use keyword fields, then reindex behind an alias with zero downtime.
#indexing#schema-design#troubleshooting
SQL ServerBeginnerError 8152 never said which column. Message 2628 on SQL Server 2019+ (or trace flag 460 on 2016/2017) names it. Then fix the data or the column, and watch for silent truncation.
#data-types#troubleshooting#t-sql
MongoDBBeginnerA server selection timeout means the driver can't reach the cluster; a pool timeout means you've run out of connections. How to diagnose each, including the serverless one-client-per-request trap.
#configuration#nosql#troubleshooting
MySQLBeginnerThe error points at a query that returned arbitrary values. Fix it with aggregates, primary-key grouping, ANY_VALUE() or window functions, and keep the SQL mode on.
#configuration#troubleshooting
RedisIntermediateOne slow command blocks every client. Find it with SLOWLOG and LATENCY DOCTOR, then replace KEYS with SCAN, split big keys, delete with UNLINK and tame fork pauses.
#caching#performance#troubleshooting
Learning paths
LEVEL 01
Tables, keys, joins and your first indexes. Build intuition that lasts.
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LEVEL 02
Query plans, transactions, replication and schema design trade-offs.
Browse intermediate articles →
LEVEL 03
Storage engines, concurrency control, internals and extreme tuning.
Browse advanced articles →
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