You don't write to the WAL on a batch.

> the author tested correctness after a crash.

You mean the LLM?

It seems to me that neither the old nor the new version of the code is really "durable" as I would understand the word. The old version made a write syscall per batch, but doesn't say it also did an fsync per batch. The new version writes data to an mmap'ed file, and calls fsync in the background.

So both versions are "durable" in the sense that written data is preserved even if the process gets killed, because it's in the OS page cache. But in both versions, a write can be completed before the data actually makes it to disk, so a power failure will lose acknowledged writes.

Fsync is often used when the data doesn't truly need to be on disk, because there aren't very good write ordering APIs exposed, even if that's all you truly need.

bool getSchemaSizes(size_t * expectedBatchSize, size_t * expectedEntriesPerBlock) { ... }

size_t expectedEntriesPerBlock, expectedBatchSize;

getSchemaSizes(&expectedEntriesPerBlock, &expectedBatchSize)

initBloomFilter(expectedEntriesPerBlock)