immediate Updates and lazy cost evaluation #75

karlmcguire · 2019-09-27T22:15:18Z

This PR addresses the Set/Del race condition by putting Dels on the same internal buffer, as well as immediately updating Set values and eventually updating the corresponding cost.

Costs can also now be calculated using the config.Coster function.

This change is

manishrjain

Comments.

Reviewed 5 of 5 files at r1.
Reviewable status: all files reviewed, 10 unresolved discussions (waiting on @jarifibrahim and @karlmcguire)

cache.go, line 98 at r1 (raw file):

	// is ran after Set is called for a new item or an item update with a cost
	// param of 0.
	Coster func(value interface{}) int64

Cost

cache.go, line 188 at r1 (raw file):

		return false
	}
	i := &item{itemNew, c.keyToHash(key), value, cost}

and here as well (see below)

cache.go, line 189 at r1 (raw file):

	}
	i := &item{itemNew, c.keyToHash(key), value, cost}
	// attempt to immediately update hashmap value and set flag to update so the

Attempt to

cache.go, line 194 at r1 (raw file):

		i.flag = itemUpdate
	}
	// attempt to send item to policy

Attempt to

cache.go, line 209 at r1 (raw file):

		return
	}
	c.setBuf <- &item{itemDelete, c.keyToHash(key), nil, 0}

&item{
  flag: ...,
  hash: ...,
}

cache.go, line 219 at r1 (raw file):

	for i := range c.setBuf {
		// calculate item cost value if new or update
		if (i.flag == itemNew || i.flag == itemUpdate) && i.cost == 0 {

i.cost == 0 && c.coster && i.flag != itemDelete

policy.go, line 192 at r1 (raw file):

func (p *defaultPolicy) Update(key uint64, cost int64) {
	p.Lock()
	defer p.Unlock()

Avoid a defer here.

policy.go, line 198 at r1 (raw file):

func (p *defaultPolicy) Cost(key uint64) int64 {
	p.Lock()
	defer p.Unlock()

cost, found = ...
p.Unlock()
if found { return cost }
return -1

policy.go, line 244 at r1 (raw file):

func (p *sampledLFU) updateIfHas(key uint64, cost int64) (updated bool) {
	if prev, exists := p.keyCosts[key]; exists {
		// Update the cost of the existing key. For simplicity, don't worry about evicting anything

Keep the comment.

store.go, line 111 at r1 (raw file):

func (m *lockedMap) Update(key uint64, value interface{}) bool {
	m.Lock()
	defer m.Unlock()

Take a sweep across the entire code base. And see what all defers you can get rid of.

ben-manes · 2019-09-27T23:15:10Z

Is there a reason you prefer cost and Coster versus the Java terms (weight and Weigher)?(When refer you referred to the entry's size in your article, "a heavy item could displace many lightweight items", you used weight as the metaphor)

karlmcguire · 2019-09-28T17:50:43Z

I was just going to change it to Cost, but I like the idea of using Weigher for the reason you mentioned... I will check with @manishrjain.

karlmcguire

Dismissed @manishrjain from 10 discussions.
Reviewable status: 1 of 5 files reviewed, all discussions resolved (waiting on @jarifibrahim and @manishrjain)

cache.go, line 98 at r1 (raw file):