Comment by markpapadakis | Hacker News Reader

Comment by markpapadakis | Hacker News Reader

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Yes, single threaded, because the contention to the various files and the cost of serialisation would likely negate the benefits of using multiple threads.

Network I/O is obviously asynchronous - you may want to check the codebase. Disk I/O is synchronous, but: - uses sendfile() and read readahead() to reduce or eliminate the likelihood of blocking reads: see here please https://github.com/phaistos-networks/TANK/issues/14#issuecom...

- AIO is either broken or supported on XFS (depending on kernel release, and also in the past, appending to a file on an XFS fs could block and degrade performance). But not using DirectI/O so writes end up in memory and only get flushed if it hits the commit count, or periodically - so, particularly for local disks, HDDs or SSDs, this in practice never blocks for more than a few ms when flushing, if at all.

> Yes, single threaded, because the contention to the various files and the cost of serialisation would likely negate the benefits of using multiple threads.

Multithreaded does not mean multiple files.

> But not using DirectI/O so writes end up in memory and only get flushed if it hits the commit count, or periodically - so, particularly for local disks, HDDs or SSDs, this in practice never blocks for more than a few ms when flushing, if at all.

Unless you are actually using it under a high throughput scenario which is why you would use a lib like this. It will work great until you hit the actual flush point, then possibly block for seconds even minutes.

If your performance needs are high, mandating XFS is not unreasonable.

It's totally unreasonable to mandate a particular FS for modern general purpose software.

Multiple files does mean multiple threads. Unless you manage to run this without a modern operating system.

> It's totally unreasonable to mandate a particular FS for modern general purpose software.

That is completely debatable. We are talking about a "a high performance distributed log service". Not a word processor.

> Multiple files does mean multiple threads.

Which is something entirely different from what I said...

You are making all kinds of assumptions without knowing anything about the implementation.

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