README.md

AnchorHash - using less memory

This is a version that uses only half the memory for storing state, as compared to the version in the paper. It makes exactly the same hashing decisions and has exactly the same key lookup speed. The only difference is that each bucket remove takes slightly longer (order of a key lookup operation vs. O(1)). Bucket addition time is unchanged.

Code

This code is a direct replacement to AnchorHashQre.cpp and AnchorHashQre.hpp.

Try it

Go into the speed directory, run make, run the python script, and plot

Algorithm

INITWRAPPER(a,S)                // a anchor capacity, S list of resources, a>=|S|
  M←∅
  for i∈(0,1,...,|S|−1) do
    M←M∪{(i,S[i])}              // mapping from bucket to resource
  INITANCHOR(a,|S|)

GETRESOURCE(k)                  // compute resource for key k
  b←GETBUCKET(hash(k))          // convert key to int (e.g., rand(seed=k)) and call anchorHash
  ξ←M(b)
  return ξ

ADDRESOURCE(ξ)
  b←ADDBUCKET( )
  M←M∪{(b,ξ)}

REMOVERESOURCE(ξ)
  b←INV_M(ξ)
  M←M\{(b,ξ)}
  REMOVEBUCKET(b)

INITANCHOR(a,w)                 // a anchor size (capacity), w number of workers (size)
  A[b]←0 for b=0,1,...,a−1      // W_b←0 for b∈A
  R←∅                           // empty stack
  N←w                           // mumber of initially working buckets
  K[b]←b for b=0,1,...,a−1
  for b=a−1 downtow do          // remove initially unused buckets
    R.push(b)
    A[b]←b

BUCKETATVIEW(b,v)               // find who replaced b at view size v
  while A[b]>=v do              // b is removed for view size v
    b←K(b)                      // search for W_v[b]
  return b

GETBUCKET(k)
  b←hash(k) mod a               // can use k if calling through wrapper as it is already hash(key)
  while A[b]>0 do               // b is removed
    h←h_b(k)                    // h←hash(b,k) mod A[b] OR k←rand(seed=k), h←k mod A[b]
    b←BUCKETATVIEW(h,A[b])
  return b

ADDBUCKET( )
  b←R.pop()
  N←N+ 1
  A[b]←0                        // W←W ∪ {b}, delete W_b
  K[b]←b
  return b

REMOVEBUCKET(b)
  R.push(b)
  h←BUCKETATVIEW(N-1,N)
  K[b]←h
  N←N−1
  A[b]←N                        // W_b←W\b, A[b]←|W_b|