SQL Server34
General18
PostgreSQL17
MongoDB12
MySQL11
Oracle Database9
SQLite8
Redis7
Apache Hadoop5
Apache Cassandra3
Elasticsearch2
IBM Db22
Microsoft Access2
Apache CouchDB1
ClickHouse1
Cloud Firestore1
CockroachDB1
Couchbase1
DuckDB1
Google BigQuery1
InfluxDB1
Milvus1
Neo4j1
Qdrant1
ScyllaDB1
Snowflake1
Supabase1
TiDB1
TimescaleDB1Articles
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ElasticsearchIntermediateYellow means missing replicas and red means missing primaries. Use the allocation explain API to find the exact cause: replica count, disk watermarks, allocation filters or failed retries.
#configuration#nosql#troubleshooting
MongoDBIntermediateThe 100 MB blocking-sort limit means your index doesn't provide the sort order. Build compound indexes with the ESR rule, order pipeline stages correctly, and know when allowDiskUse is fine.
#indexing#nosql#performance
Oracle DatabaseIntermediateYour long query needed undo that was already overwritten. How Oracle read consistency uses undo, how to read V$UNDOSTAT, and why committing inside a loop causes it.
#configuration#mvcc#troubleshooting
MySQLIntermediateStale reads and 2 a.m. lag spikes usually come down to single-threaded apply, tables without primary keys and giant transactions. Diagnose and fix each one.
#performance#replication#troubleshooting
SQL ServerBeginnerIt's caching by design, not a leak, but the default limit is 'everything'. How to set max server memory and tell real memory pressure from a full buffer pool.
#configuration#internals#performance
SQL ServerIntermediateNOLOCK doesn't just risk dirty reads. It can skip rows, count rows twice and fail with error 601. Read Committed Snapshot Isolation removes the blocking without the wrong answers.
#concurrency#locking#transactions
PostgreSQLAdvancedA one-line migration can freeze every query on a table. lock_timeout, CREATE INDEX CONCURRENTLY, NOT VALID constraints and expand-and-contract keep schema changes online.
#indexing#locking#migrations
GeneralIntermediateSelect-then-insert breaks under concurrency. Use a unique constraint plus one atomic statement: ON CONFLICT, ON DUPLICATE KEY UPDATE, or UPDLOCK/SERIALIZABLE in SQL Server.
#concurrency#schema-design#transactions
SQLiteBeginnerStill getting SQLITE_BUSY with a timeout set? The default timeout is zero and deferred transactions can't wait. WAL mode, busy_timeout and BEGIN IMMEDIATE fix most cases.
#concurrency#locking#troubleshooting
PostgreSQLIntermediateMVCC means Postgres doesn't store a row count. Make exact counts cheaper, get instant estimates from the planner, and keep exact counters when you really need them.
#internals#mvcc#performance
GeneralBeginnerThe N+1 query problem: each query takes 1 ms, but there are 301 of them. How to spot it, fix it with eager loading and avoid the cartesian-explosion overcorrection.
#orm#performance#troubleshooting
SQL ServerIntermediateExecution plans tell you exactly how SQL Server ran your query. Learn which operators matter, how to spot bad estimates and what the warnings really mean.
#execution-plans#performance#t-sql
