New class zict.Cache

[crusaderky]

• Closes Spill to disk may cause data duplication distributed#3756
• Blocks Prevent data duplication on unspill distributed#5936

[jakirkham]

Have we looked at cachetools?

[crusaderky]

cachetools.Cache does a lot more than this new class - because it's not composable - and also a lot less, for the exact same reason.

Technically speaking,
cachetools.Cache(maxsize, weightfunc)
is functionally identical to
zict.Cache({}, zict.LRU(maxsize, {}, weight=weightfunc).

Everything else that zict allows - namely,

• having a custom subclass of zict.Func as the data, or
• having a weakref.WeakValueDict as the cache

both of which are key features here, cachetools does not do.

[fjetter]

I think we should briefly talk about naming but otherwise this looks good!

[fjetter]

Do you have an example where update_on_set=False is helpful?

[crusaderky]

Not in distributed.
It boils down to the temporal locality patterns of the library user. Sometimes writing a key/value pair does not imply likelihood that the same key will be read back sooner than the rest.

For example, somebody may write the output of a nightly backup batch job to s3fs or some other very slow filesystem; being a backup, 9 times out of 10 nobody is going to read it back. When people do want to read it back though, they are very likely to access the same files multiple times (assuming the backup is not just dumped back on top of live).

[fjetter]

It is a bit confusing having the Cache and WeakRefCache classes in here although WeakRefCache is not a Cache. Maybe one of the classes should be renamed?

[fjetter]

Maybe this one should be called WeakValueMapping to stick to zict nomenclature?

[crusaderky]

renamed

[jakirkham]

Guessing the conflicts are related to PR ( #66 )?

[crusaderky]

fixed conflicts