78 lines
2.3 KiB
Go
78 lines
2.3 KiB
Go
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package graviton
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import "fmt"
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import "math"
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import "crypto/rand"
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// Random returns a random key,value from the tree, provided a tree has keys
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// the following are limitations
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// a tree containing 0 key, value pairs will return err
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// randomness depends on number of keys, if tree contains only 1 value, it will be ported etc
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func (t *Tree) Random() (k, v []byte, err error) {
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return t.random(t.root)
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}
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func (t *Tree) random(cnode node) (k, v []byte, err error) {
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switch node := cnode.(type) {
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case *inner:
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if node.loaded_partial { // if node is loaded partially, load it fully now
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if err = node.loadinnerfromstore(t.store); err != nil {
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return
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}
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}
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left, right := node.left, node.right
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if left != nil && right != nil { // we have an option to choose from left or right randomly
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var rbyte [1]byte
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if _, err = rand.Read(rbyte[:]);err != nil {
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return
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}
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if rbyte[0] & 1 == 1 {
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return t.random(right) // descend further
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}
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return t.random(left) // descend further
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}
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if right != nil {
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return t.random(right) // descend further without any option
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}
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if left != nil {
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return t.random(left) // descend further without any option
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}
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// we can only reach here if a tree has both left,right nil, ie an empty tree
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err = ErrNoMoreKeys
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return
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case *leaf:
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if node.loaded_partial { // if leaf is loaded partially, load it fully now
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if err = node.loadfullleaffromstore(t.store); err != nil {
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return
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}
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}
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return node.key, node.value, nil
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default:
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return k, v, fmt.Errorf("unknown node type, corruption")
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}
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}
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// estimate number of keys that exist in the tree
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// very crude but only used for use display
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func (t *Tree) KeyCountEstimate() (count int64) {
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c := t.Cursor()
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var depth_array []int
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var floatsum float64
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for _, _, err := c.First(); err == nil ; _, _, err = c.Next() {
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floatsum += float64( len(c.node_path))
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depth_array = append(depth_array, len(c.node_path))
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if len(depth_array) >= 20 {
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break
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}
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}
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if len(depth_array) <= 4 {
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return int64(count)
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}
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avg := floatsum / float64(len(depth_array)+1)
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return int64 ( math.Exp2(avg))
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}
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