Library
150 results
SQLiteIntermediateAn ordered procedure for SQLITE_BUSY with a verification for each step, a script that reproduces the contention, and the matching settings for Python, Node and Go drivers.
#concurrency#locking#troubleshooting
PostgreSQLBeginnerThe index exists, but the plan still shows a scan. Nine common reasons the optimizer can't (or shouldn't) use your index, and how to fix each one.
#execution-plans#indexing#performance
SQLiteIntermediateWhat SQLITE_BUSY means, where it is returned in rollback-journal and WAL mode, why a timeout sometimes does nothing, the extended codes, and how to find who holds the lock.
#concurrency#internals#locking
SQL ServerIntermediateSame proc, same code, suddenly 100× slower, and fast again when you run it in SSMS. Here's how parameter sniffing causes it, how to prove it and the fixes that actually hold.
#execution-plans#performance#troubleshooting
GeneralIntermediateAdjacency lists, materialized paths, nested sets and closure tables compared, and why a parent_id column plus a recursive CTE is the right default.
#data-modeling#schema-design
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
