[Question] why deleting value by object key is slow ?

[orangemi]

You mentioned in README.md:

Then I discovered why some of the fast algorithms where so slow - they used delete cache[key] which is much slower than cache[key] = value, much much slower.

Do you have any tip about why deleting value by object key is slow ? I'm just curious about the reason.

[wesleytodd]

AFAIK, JS uses hidden classes to optimize property lookup on objects with the same shape. Deleting a property makes the current hidden class invalid, so the VM has to use a much slower generic representation.

[ibigbug]

@orangemi You may check out this article: https://github.com/petkaantonov/bluebird/wiki/Optimization-killers

[orangemi]

@ibigbug nice!

[dominictarr]

reopening this issue because the linked article did not answer the question for me.
hashlru should certainly be putting things the cache into hash table mode. I can see that deleting from a hidden class object and changing to a hash table object would be expensive, but I don't know why deleting from a hash table is more expensive...

Hmm, it just occured to me that I am using incrementing integers as keys. maybe this is handled as a special case and is not a hash table? I'll have to do another bench mark to test.

[Kikobeats]

highly related: https://mythbusters.js.org/#/v8-tips/freeing-memory