Durability

2 articles

Tech 16 Sep 2026 5 min read

fsync on a File Does Not Persist Its Directory Entry

A successful fsync() on a regular file does not, by itself, guarantee that the directory entry naming that file has reached persistent storage. Linux documents this boundary explicitly: file synchronization covers the file’s data and associated metadata, while persistence of the containing directory entry requires an fsync() on a file descriptor for that directory. This distinction matters when software creates a new file or atomically replaces an existing pathname. File contents and pathname metadata are separate pieces of filesystem state, and a crash can test the durability boundary between them.

Linux Filesystem

Database 15 Sep 2026 6 min read

PostgreSQL Full-Page Writes Raise WAL Volume After Checkpoints

A PostgreSQL page modified for the first time after a checkpoint can generate much more WAL than a later modification to the same page. With full_page_writes enabled, the first protected change records a full page image so crash recovery can reconstruct a page even if an operating-system failure interrupts a physical page write. That protection creates a recurring WAL pattern tied to checkpoint boundaries. A checkpoint resets the condition for pages, and subsequent writes gradually encounter pages that need a new full page image.

PostgreSQL Database