> On Oct 29, 2018, at 7:13 PM, Simon Slavin <[email protected]> wrote:
>
> This post is about a problem with Apple's new APFS file system. The problem
> will affect you only if you have multiple reads/writes happening at the same
> time. The problem involves merely slowing of performance, not corruption of
> databases or incorrect answers being returned by SQLite.
I finally got around to reading the article — thanks for posting the link,
Simon.
However, I don’t think the issue described in the article is relevant to SQLite
at all. The article is specifically about slowdowns in the readdir system call,
not file I/O. ("I haven't conducted a comprehensive analysis of APFS to
determine what other filesystem operations seem to acquire global kernel locks:
all I know is readdir() does.”) But there are no calls to readdir in the SQLite
3.25 source code!
Second, it’s good to see that the situation has been improved in macOS 10.14.
"It is apparent that macOS 10.14 Mojave has received performance work relative
to macOS 10.13! Overall kernel CPU time when performing parallel directory
walks has decreased substantially - to ~50% of original on some invocations!”
However, "Despite those improvements, APFS is still spending a lot of CPU time
in the kernel.”
—Jens
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