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PostgreSQLIntermediateThe old UUID performance problem came from UUIDv4's randomness, not UUIDs themselves. How UUIDv7 changes the trade-off, what the extra 8 bytes still cost and when to pick each.
#data-types#indexing#schema-design
MySQLIntermediatePage 1 takes 5 ms and page 5,000 takes 4 seconds. OFFSET reads and throws away every skipped row. Switch to keyset (cursor) pagination for constant-time pages.
#indexing#pagination#performance
PostgreSQLIntermediateA reference comparison of PostgreSQL and MySQL: storage and MVCC, isolation defaults, DDL, data types, indexes, replication, licensing and tooling, with a decision summary.
#indexing#internals#replication
MySQLIntermediateError 1205 on a simple UPDATE, from code that doesn't even use transactions. Find the blocking session, spot the missing index that's locking too much and stop it coming back.
#locking#transactions#troubleshooting
SQLiteIntermediateWhy Python raises "database is locked", how timeout, isolation_level and autocommit interact, and the working pattern for threads, worker processes, SQLAlchemy, Django and aiosqlite.
#concurrency#locking#orm
PostgreSQLIntermediateRaising max_connections to 1000 usually makes things worse. Learn why Postgres connections are expensive, where they're leaking and how PgBouncer fixes it for good.
#configuration#performance#troubleshooting
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
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
