org.h2.mvstore.CursorPos Maven / Gradle / Ivy
/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.mvstore;
/**
* A position in a cursor.
* Instance represents a node in the linked list, which traces path
* from a specific (target) key within a leaf node all the way up to te root
* (bottom up path).
*/
public class CursorPos
{
/**
* The page at the current level.
*/
public Page page;
/**
* Index of the key (within page above) used to go down to a lower level
* in case of intermediate nodes, or index of the target key for leaf a node.
* In a later case, it could be negative, if the key is not present.
*/
public int index;
/**
* Next node in the linked list, representing the position within parent level,
* or null, if we are at the root level already.
*/
public CursorPos parent;
public CursorPos(Page page, int index, CursorPos parent) {
this.page = page;
this.index = index;
this.parent = parent;
}
/**
* Searches for a given key and creates a breadcrumb trail through a B-tree
* rooted at a given Page. Resulting path starts at "insertion point" for a
* given key and goes back to the root.
*
* @param page root of the tree
* @param key the key to search for
* @return head of the CursorPos chain (insertion point)
*/
public static CursorPos traverseDown(Page page, Object key) {
CursorPos cursorPos = null;
while (!page.isLeaf()) {
int index = page.binarySearch(key) + 1;
if (index < 0) {
index = -index;
}
cursorPos = new CursorPos(page, index, cursorPos);
page = page.getChildPage(index);
}
return new CursorPos(page, page.binarySearch(key), cursorPos);
}
/**
* Calculate the memory used by changes that are not yet stored.
*
* @param version the version
* @return the amount of memory
*/
int processRemovalInfo(long version) {
int unsavedMemory = 0;
for (CursorPos head = this; head != null; head = head.parent) {
unsavedMemory += head.page.removePage(version);
}
return unsavedMemory;
}
@Override
public String toString() {
return "CursorPos{" +
"page=" + page +
", index=" + index +
", parent=" + parent +
'}';
}
}