hcache on tmpfs?

[void]

Hello Cameron, I've replied in-line

On Fri, Mar 31, 2023 at 10:22:49AM +1100, Cameron Simpson wrote:

>"memory based" might just mean memory mapped - kytotocabinet still has
>persistent storage. Using a tmpfs will mean (a) it uses your physical
>RAM (or possibly swap?) even when you're not using mutt and (b) the db
>will vanosh on reboot.
>
>I've used kyotocabinet elsewhere but do not know much, if anything,
>about its internals.
>
>Are you asking about picking a db backend (eg kyoto versus dbm)?

yes. I have several choices when building mutt:

HCACHE_BDB     : off
HCACHE_GDBM    : off
HCACHE_KYOTOCABINET: off
HCACHE_LMDB    : on
HCACHE_NONE    : off
HCACHE_QDBM    : off
HCACHE_TOKYOCABINET: off

The question is really about "is it worth putting kyotocabinet in there
when ~/tmp is already a tmpfs and it uses (mostly? mainly?) ram

>Subjectively, I'd have thought for moderate data they'd be similar on a
>tmpfs. If you're prepared to rebuild the whole hcache after a reboot
>(which of course might be very infrequent for you) it still may not
>matter.

Yes. The machine is on 24/7 apart from OS upgrades and similar

>Can you qualify what your concerns are here?

It's just interest. I want as fast as possible and it's not an issue if
headers have to be re-fetched after a boot because the connection is
also fast. I use imap with my ISP. I frequently press '$' to resync
last-read pointers with the imap server. Maybe I can tell mutt to do
that automatically every 5 mins. my concern is only that if/when headers
have to be re-fetched that already-read email doesn't have the unread
flag set subsequently.

>I use an hcache. On persistent storage, which is an SSD for me. My
>"python" folder has 157000 messages in it and opening mutt on it and
>then closing it just took about 20 seconds including eyeballing the top
>line to read the message count. This mutt was built with tokyocabinet,
>which I expect is used for the hache (nothing else would have any use
>for it).

I'd recomment lmdb in your context if you need persistent storage. 
Have been v impressed with lmdb. I also have thousands of emails 
spread across different folders. My context is using a rpi4b (8GB) with
usb3-connected hard drive. Right now, with $tmpdir pointing to a tmpfs
mount, and with hcache still pointing to the HD, (and with a zfs
filesystem), mutt is veru useable and quick even on this limited
hardware.
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