unix
9 minLinux Disk Full Errors: Blocks, Inodes, Deleted Files, and Safe Cleanup
Diagnose ENOSPC when disk usage looks confusing, including exhausted inodes and deleted files still held open.
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Q&A
Q&AWhy can a Linux filesystem be full when du shows free space?
Inodes may be exhausted, or deleted files may still be held open by running processes.
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Compare df -h with df -i. If block usage and directory totals disagree, inspect open-but-deleted files with lsof +L1. A process retains allocated blocks until it closes the file; restart or signal the owning service through its safe lifecycle after confirming the file is disposable.
unix
18 minLinux Under Load: Epoll, File Descriptors, OOM, TCP Queues, and VFS
Connect kernel readiness APIs, resource limits, cgroups, socket queues, page cache, and inode behavior to production symptoms.
databases
9 minMySQL InnoDB: Transactions, Indexes, and Reading EXPLAIN
Understand InnoDB's clustered primary key, secondary-index lookups, transaction behavior, and practical query-plan analysis.
databases
8 minPostgreSQL concurrent indexes: reason about locks, retries, and invalid states
Use concurrent index builds without assuming they are lock-free or all-or-nothing.
Q&A
Q&AHow does the InnoDB primary key affect secondary indexes?
InnoDB secondary-index entries carry the primary-key value used to find the clustered row.
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InnoDB organizes table rows by the clustered primary key. Secondary indexes store their indexed columns plus the primary-key value, so a query requesting columns absent from the secondary index may need a second lookup. Wide primary keys therefore increase the footprint of every secondary index.
databases
10 minPostgreSQL MVCC and Indexes: Reads, Vacuum, and Query Plans
Connect PostgreSQL's multi-version concurrency control to transaction visibility, vacuum work, index choice, and EXPLAIN output.
databases
10 minFix Slow SQL: N+1 Queries, Missing Indexes, and Bad Cardinality Estimates
A systematic approach to diagnosing ORM query explosions and slow database plans without guessing at indexes.