[Akonadi] [Bug 338402] File system cache is inneficient : too many file per directory

[Martin Steigerwald]

https://bugs.kde.org/show_bug.cgi?id=338402

--- Comment #5 from Martin Steigerwald <ms at teamix.de> ---
Dan, I agree that lookup of an individual file will be fast with Ext4, BTRFS,
XFS, yet it causes other issues:

- updatedb
- backup: my rsync based backup to eSATA 2 TB harddisk takes way more than one
hour now. It was much quicker at some time. It maybe have also different
reasons, but my bet that the large file_db_data directories contribute to that.
It may likely be way faster with btrfs send/receive, but there are a lot of
backup solutions out there, which may have issues with a folder like this.
- any disk usage calculator like filelight will have delays on it (I showed the
5 minute time for du -sch, admitted, this has ecryptfs in between, that visibly
seems to make the performance worse)
- so add ecryptfs to the list, I did a du -sch over the uncrypted version and
it is way faster than the 5 minutes.
- or maybe NFS based setups as well
- and storage appliances with limits

Its not just Akonadi living alone with a superfast PCIe M2 SSD.

And whats about Akonadi on Windows? I bet NTFS may cope, but do you know? Or
Mac OS X with HFS+, how about that?


So arguing modern Linux filesystem can handle these amounts of files is like
arguing:

Ey, we have 16 GiB of RAM available, so why don´t reserve and use it all, even
if we do not need it.

So what is the rationale for caching that much? What is the actual benefit it
provides. I fail to see it.

I will now set that account to offline caching on my laptop. Maybe then I will
see some use. And as it already insists on keeping 7 GiB of my IMAP account
stored locally, I don´t bother if it also downloads the rest of it.

According to filelight file_db_data is the largest folder! Not even Baloo´s
email index is that large. It has just 5,3 GiB. And this one actual provides a
benefit. A huge one. And it has it in way less files.

That said, I know found that Icedove, which I used at some time also has 4,2
GiB locally. But I instructed it to keep mails for offline usage, when I
remember correctly.

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