/*
* Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.store;
import java.lang.reflect.Array;
import org.h2.engine.Session;
import org.h2.util.CacheObject;
/**
* A page. Format:
* <ul><li>0-3: parent page id (0 for root)
* </li><li>4-4: page type
* </li><li>page-type specific data
* </li></ul>
*/
public abstract class Page extends CacheObject {
/**
* This is the last page of a chain.
*/
public static final int FLAG_LAST = 16;
/**
* An empty page.
*/
public static final int TYPE_EMPTY = 0;
/**
* A data leaf page (without overflow: + FLAG_LAST).
*/
public static final int TYPE_DATA_LEAF = 1;
/**
* A data node page (never has overflow pages).
*/
public static final int TYPE_DATA_NODE = 2;
/**
* A data overflow page (the last page: + FLAG_LAST).
*/
public static final int TYPE_DATA_OVERFLOW = 3;
/**
* A b-tree leaf page (without overflow: + FLAG_LAST).
*/
public static final int TYPE_BTREE_LEAF = 4;
/**
* A b-tree node page (never has overflow pages).
*/
public static final int TYPE_BTREE_NODE = 5;
/**
* A page containing a list of free pages (the last page: + FLAG_LAST).
*/
public static final int TYPE_FREE_LIST = 6;
/**
* A stream trunk page.
*/
public static final int TYPE_STREAM_TRUNK = 7;
/**
* A stream data page.
*/
public static final int TYPE_STREAM_DATA = 8;
private static final int COPY_THRESHOLD = 4;
/**
* When this page was changed the last time.
*/
protected long changeCount;
/**
* Copy the data to a new location, change the parent to point to the new
* location, and free up the current page.
*
* @param session the session
* @param newPos the new position
*/
public abstract void moveTo(Session session, int newPos);
/**
* Write the page.
*/
public abstract void write();
/**
* Insert a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @param x the value to insert
* @return the (new) array
*/
@SuppressWarnings("unchecked")
public static <T> T[] insert(T[] old, int oldSize, int pos, T x) {
//以下old不像其他两个insert的代码中那样判断是否为null，主要是因为此方法的old是SearchRow[] rows和Row[] rows;
//这两个字段在create方法中都赋值了，所以问题不大
T[] result;
if (old.length > oldSize) {
//old会多申请COPY_THRESHOLD=4个元素，oldSize是真实的有效元素个数，所以old.length > oldSize时，
//说明还有足够的空间
result = old;
} else {
// according to a test, this is as fast as "new Row[..]"
result = (T[]) Array.newInstance(old.getClass().getComponentType(), oldSize + 1 + COPY_THRESHOLD);
//当pos等于0时就不复制了，是因为下面System.arraycopy(old, pos, result, pos + 1, oldSize - pos);
//会为result预留一个位置(pos+1)说明当pos是0是，result数姐从下标1的地方复制，
//紧接着result[pos] = x;就把x放位下标为o的位置处了。
if (pos > 0) {
System.arraycopy(old, 0, result, 0, pos); //复制pos位置前的元素
}
}
if (oldSize - pos > 0) { //把pos位置开始的元素向后移
System.arraycopy(old, pos, result, pos + 1, oldSize - pos);
}
result[pos] = x;
return result;
}
/**
* Delete a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @return the (new) array
*/
@SuppressWarnings("unchecked")
public
static <T> T[] remove(T[] old, int oldSize, int pos) {
T[] result;
if (old.length - oldSize < COPY_THRESHOLD) {
result = old;
} else {
// according to a test, this is as fast as "new Row[..]"
result = (T[]) Array.newInstance(
old.getClass().getComponentType(), oldSize - 1);
System.arraycopy(old, 0, result, 0, Math.min(oldSize - 1, pos));
}
if (pos < oldSize) {
System.arraycopy(old, pos + 1, result, pos, oldSize - pos - 1);
}
return result;
}
/**
* Insert a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @param x the value to insert
* @return the (new) array
*/
protected static long[] insert(long[] old, int oldSize, int pos, long x) {
long[] result;
if (old != null && old.length > oldSize) {
result = old;
} else {
result = new long[oldSize + 1 + COPY_THRESHOLD];
//未像insert(int[], int, int, int)那样判断old是否为null
if (pos > 0) {
System.arraycopy(old, 0, result, 0, pos);
}
}
if (old != null && oldSize - pos > 0) {
System.arraycopy(old, pos, result, pos + 1, oldSize - pos);
}
result[pos] = x;
return result;
}
/**
* Delete a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @return the (new) array
*/
protected static long[] remove(long[] old, int oldSize, int pos) {
long[] result;
if (old.length - oldSize < COPY_THRESHOLD) {
result = old;
} else {
result = new long[oldSize - 1];
System.arraycopy(old, 0, result, 0, pos);
}
System.arraycopy(old, pos + 1, result, pos, oldSize - pos - 1);
return result;
}
/**
* Insert a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @param x the value to insert
* @return the (new) array
*/
protected static int[] insert(int[] old, int oldSize, int pos, int x) {
int[] result;
if (old != null && old.length > oldSize) {
result = old;
} else {
result = new int[oldSize + 1 + COPY_THRESHOLD];
if (pos > 0 && old != null) {
System.arraycopy(old, 0, result, 0, pos);
}
}
if (old != null && oldSize - pos > 0) { //把pos位置开始的元素向后移
System.arraycopy(old, pos, result, pos + 1, oldSize - pos);
}
result[pos] = x;
return result;
}
/**
* Delete a value in an array. A new array is created if required.
*
* @param old the old array
* @param oldSize the old size
* @param pos the position
* @return the (new) array
*/
protected static int[] remove(int[] old, int oldSize, int pos) {
int[] result;
if (old.length - oldSize < COPY_THRESHOLD) {
result = old;
} else {
result = new int[oldSize - 1];
System.arraycopy(old, 0, result, 0, Math.min(oldSize - 1, pos));
}
if (pos < oldSize) {
System.arraycopy(old, pos + 1, result, pos, oldSize - pos - 1);
}
return result;
}
/**
* Add a value to a subset of the array.
*
* @param array the array
* @param from the index of the first element (including)
* @param to the index of the last element (excluding)
* @param x the value to add
*/
protected static void add(int[] array, int from, int to, int x) {
for (int i = from; i < to; i++) {
array[i] += x;
}
}
/**
* If this page can be moved. Transaction log and free-list pages can not.
*
* @return true if moving is allowed
*/
//以下三个子类覆盖了些方法，说明这三种页面不能移动
//6. TYPE_FREE_LIST org.h2.store.PageFreeList
//7. TYPE_STREAM_TRUNK org.h2.store.PageStreamTrunk
//8. TYPE_STREAM_DATA org.h2.store.PageStreamData
public boolean canMove() {
return true;
}
}