btree-double-fsync-per-mutation

Status: IN

B-tree mutations pay for `os.fsync()` twice: once when writing the WAL entry (`btree.py:137`) and again when committing the page to the data file (`btree.py:105`), with the WAL truncated only after the data file sync confirms durability.

Source: entries/2026/05/29/topic-fsync-vs-fdatasync.md

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