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immutable BTree works

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This commit is contained in:
Andreas Rumpf 2017-05-12 22:23:18 +02:00
commit 1f1edeb23f
1 changed files with 28 additions and 28 deletions
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52
src/karaxdb/btree.nim
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@ -5,7 +5,7 @@
## to off load pages to a file system or to send it over the wire. ## to off load pages to a file system or to send it over the wire.
const const
M = 128 # max children per B-tree node = M-1 M = 4 # max children per B-tree node = M-1
# (must be even and greater than 2) # (must be even and greater than 2)
Mhalf = M div 2 Mhalf = M div 2
@ -106,40 +106,40 @@ proc insert(h: Node, key: Key, val: Val, ht: int): Node =
return if h.m < M: nil else: split(h) return if h.m < M: nil else: split(h)
proc insertPs(h: Node, key: Key, val: Val, ht: int): (Node, Node) = proc insertPs(h: Node, key: Key, val: Val, ht: int): (Node, Node) =
#var t = Entry(key: key, val: val, next: nil)
var newKey = key
var j = 0 var j = 0
var hh = Node(m: h.m, isInternal: h.isInternal) var hh = Node(m: h.m, isInternal: h.isInternal)
for i in 0 ..< h.m: hh.keys[i] = h.keys[i]
if ht == 0: if ht == 0:
assert(not h.isInternal) assert(not h.isInternal)
while j < h.m: while j < h.m:
if less(key, h.keys[j]): break if less(key, h.keys[j]): break
inc j inc j
for i in countdown(h.m, j+1): for i in countdown(h.m, j+1): shallowCopy(hh.vals[i], h.vals[i-1])
shallowCopy(hh.vals[i], h.vals[i-1]) for i in 0 ..< j: shallowCopy(hh.vals[i], h.vals[i])
for i in countdown(h.m, j+1): hh.keys[i] = hh.keys[i-1]
hh.vals[j] = val hh.vals[j] = val
hh.keys[j] = key
else: else:
assert h.isInternal assert h.isInternal
var newLink: Node = nil # could optimize this copying here:
for i in 0 ..< h.m: hh.links[i] = h.links[i]
while j < h.m: while j < h.m:
if j+1 == h.m or less(key, h.keys[j+1]): if j+1 == h.m or less(key, h.keys[j+1]):
let (u, root) = insertPs(h.links[j], key, val, ht-1) let (root, r) = insertPs(h.links[j], key, val, ht-1)
if u == nil: return (u, root)
hh.links[j] = root hh.links[j] = root
newKey = u.keys[0] if r == nil:
newLink = u return (hh, nil)
else:
inc j inc j
for i in countdown(h.m, j+1):
hh.links[i] = hh.links[i-1]
hh.keys[i] = hh.keys[i-1]
hh.links[j] = r
hh.keys[j] = r.keys[0]
break break
inc j inc j
for i in countdown(h.m, j+1):
hh.links[i] = h.links[i-1]
hh.links[j] = newLink
for i in countdown(h.m, j+1):
hh.keys[i] = h.keys[i-1]
hh.keys[j] = newKey
inc hh.m inc hh.m
return if hh.m < M: (nil, nil) else: (split(hh), hh) return if hh.m < M: (hh, nil) else: (hh, split(hh))
proc put(b: var BTree; key: Key; val: Val) = proc put(b: var BTree; key: Key; val: Val) =
let u = insert(b.root, key, val, b.height) let u = insert(b.root, key, val, b.height)
@ -156,13 +156,11 @@ proc put(b: var BTree; key: Key; val: Val) =
inc b.height inc b.height
proc putPs(b: BTree; key: Key; val: Val): BTree = proc putPs(b: BTree; key: Key; val: Val): BTree =
let v = insertPs(b.root, key, val, b.height) let (root, u) = insertPs(b.root, key, val, b.height)
result.n = b.n + 1 result.n = b.n + 1
result.height = b.height result.height = b.height
let u = v[0]
let root = v[1]
if u == nil: if u == nil:
result.root = Node(m: 0, isInternal: false) result.root = root
return return
# need to split root # need to split root
let t = Node(m: 2, isInternal: true) let t = Node(m: 2, isInternal: true)
@ -231,15 +229,17 @@ proc main =
echo b2.height echo b2.height
when true: when true:
var b1 = newBTree()
var b2 = newBTree() var b2 = newBTree()
const iters = 10_000 const iters = 60_000
for i in 1..iters: for i in 1..iters:
b2 = b2.putPs($i, $(iters - i)) b2 = b2.putPs($i, $(iters - i))
b1.put($i, $(iters - i))
for i in 1..iters: for i in 1..iters:
let x = b2.get($i) let x = b2.get($i)
if x != $(iters - i): if x != $(iters - i):
echo "got ", x, ", but expected ", iters - i echo i, "th iteration; got ", x, ", but expected ", iters - i
echo b2.n echo b2.n, " = ", b1.n
echo b2.height echo b2.height, " = ", b1.height
main() main()