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Performance

Modern Filesystems: Journaling vs Copy-on-Write, the Kernel Write Path, and Data Correctness

··3861 words·19 mins
When engineers discuss storage and file systems, the conversation often starts and stops with the classics: ext4 on Linux, NTFS on Windows, and perhaps XFS for large database servers. For decades, the dominant answer to filesystem reliability was straightforward: journaling.

PostgreSQL MVCC and Autovacuum Learnings

··1251 words·6 mins
PostgreSQL can let readers and writers work concurrently because of multi-version concurrency control, or MVCC. The trade-off is that an update usually creates a new tuple version instead of replacing the old one in place. A delete also makes a tuple obsolete without immediately removing its storage.