/*
* 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.index;
import java.util.Arrays;
import org.h2.api.ErrorCode;
import org.h2.engine.Constants;
import org.h2.engine.Session;
import org.h2.engine.SysProperties;
import org.h2.message.DbException;
import org.h2.result.SearchRow;
import org.h2.store.Data;
import org.h2.store.Page;
import org.h2.store.PageStore;
/**
* A b-tree leaf page that contains index data. Format:
* <ul>
* <li>page type: byte</li>
* <li>checksum: short</li>
* <li>parent page id (0 for root): int</li>
* <li>index id: varInt</li>
* <li>entry count: short</li>
* <li>list of offsets: short</li>
* <li>data (key: varLong, value,...)</li>
* </ul>
*/
public class PageBtreeLeaf extends PageBtree {
private static final int OFFSET_LENGTH = 2;
private final boolean optimizeUpdate;
private boolean writtenData;
private PageBtreeLeaf(PageBtreeIndex index, int pageId, Data data) {
super(index, pageId, data);
this.optimizeUpdate = index.getDatabase().getSettings().optimizeUpdate; //默认为true
}
/**
* Read a b-tree leaf page.
*
* @param index the index
* @param data the data
* @param pageId the page id
* @return the page
*/
public static Page read(PageBtreeIndex index, Data data, int pageId) {
PageBtreeLeaf p = new PageBtreeLeaf(index, pageId, data);
p.read();
return p;
}
/**
* Create a new page.
*
* @param index the index
* @param pageId the page id
* @param parentPageId the parent
* @return the page
*/
static PageBtreeLeaf create(PageBtreeIndex index, int pageId,
int parentPageId) {
PageBtreeLeaf p = new PageBtreeLeaf(index, pageId, index.getPageStore()
.createData());
index.getPageStore().logUndo(p, null);
p.rows = SearchRow.EMPTY_ARRAY;
p.parentPageId = parentPageId;
p.writeHead();
p.start = p.data.length(); //PageBtreeLeaf页头部结束的位置，即写完entryCount项后的位置
return p;
}
private void read() {
data.reset();
int type = data.readByte();
data.readShortInt();
this.parentPageId = data.readInt();
onlyPosition = (type & Page.FLAG_LAST) == 0;
int indexId = data.readVarInt();
if (indexId != index.getId()) {
throw DbException.get(ErrorCode.FILE_CORRUPTED_1,
"page:" + getPos() + " expected index:" + index.getId() +
"got:" + indexId);
}
entryCount = data.readShortInt();
offsets = new int[entryCount];
rows = new SearchRow[entryCount];
for (int i = 0; i < entryCount; i++) {
offsets[i] = data.readShortInt();
}
start = data.length();
written = true;
writtenData = true;
}
@Override
int addRowTry(SearchRow row) {
int x = addRow(row, true);
memoryChange();
return x;
}
//假设一个块128字节，写索引记录的顺序是从块尾开始，offset从块尾开始
private int addRow(SearchRow row, boolean tryOnly) {
int rowLength = index.getRowSize(data, row, onlyPosition);
int pageSize = index.getPageStore().getPageSize();
int last = entryCount == 0 ? pageSize : offsets[entryCount - 1];
//确保page剩余空间能够保存offset
if (last - rowLength < start + OFFSET_LENGTH) {
if (tryOnly && entryCount > 1) {
int x = find(row, false, true, true);
if (entryCount < 5) {
// required, otherwise the index doesn't work correctly
return entryCount / 2;
}
// split near the insertion point to better fill pages
// split in half would be:
// return entryCount / 2;
int third = entryCount / 3;
return x < third ? third : x >= 2 * third ? 2 * third : x;
}
//当索引字段值的大小超过pageSize时只存位置不存字段值
readAllRows();
writtenData = false;
onlyPosition = true;
// change the offsets (now storing only positions)
int o = pageSize;
for (int i = 0; i < entryCount; i++) {
o -= index.getRowSize(data, getRow(i), true);
offsets[i] = o;
}
last = entryCount == 0 ? pageSize : offsets[entryCount - 1];
rowLength = index.getRowSize(data, row, true);
if (SysProperties.CHECK && last - rowLength < start + OFFSET_LENGTH) {
throw DbException.throwInternalError();
}
}
index.getPageStore().logUndo(this, data);
if (!optimizeUpdate) {
readAllRows();
}
changeCount = index.getPageStore().getChangeCount();
written = false;
int x;
if (entryCount == 0) {
x = 0;
} else {
x = find(row, false, true, true);
}
start += OFFSET_LENGTH;
//x所在元素的值，是它前面的元素值-rowLength
int offset = (x == 0 ? pageSize : offsets[x - 1]) - rowLength;
//索引或内存中已有记录的情况(第一次运行完JDBC客户端程序后不删表和索引，第2次运行JDBC客户端程序添加记录就能测试)此种情况
if (optimizeUpdate && writtenData) {
if (entryCount > 0) {
byte[] d = data.getBytes();
int dataStart = offsets[entryCount - 1]; //offsets总是降序的，所以offsets[entryCount - 1]是data的最小下标
int dataEnd = offset;
//将data数组中dataStart下标开始的dataEnd - dataStart + rowLength个元素往左移到dataStart - rowLength开始处
//(即: 把数据移到dataStart位置的左边，因为dataStart前的位置还没写数据，所以整体往前挪rowLength, 右边挪出的空位置
//用来放新的row，这个row的位置就是offset)
System.arraycopy(d, dataStart, d, dataStart - rowLength, dataEnd - dataStart + rowLength);
}
index.writeRow(data, offset, row, onlyPosition);
}
//offsets这个数组内的元素是由大到小的，所以在rows中的记录最先的反而写在文件的后面
offsets = insert(offsets, entryCount, x, offset);
//为什么要entryCount + 1呢，因前经过前面一行代码后，offsets的实际长度已经增加1了，但是entryCount在后面才加1
add(offsets, x + 1, entryCount + 1, -rowLength); //x是中间位置时，从x之后的offset要减去rowLength
rows = insert(rows, entryCount, x, row);
entryCount++;
index.getPageStore().update(this);
return -1;
}
private void removeRow(int at) {
if (!optimizeUpdate) {
readAllRows();
}
index.getPageStore().logUndo(this, data);
entryCount--;
written = false;
changeCount = index.getPageStore().getChangeCount();
if (entryCount <= 0) {
DbException.throwInternalError("" + entryCount);
}
int startNext = at > 0 ? offsets[at - 1] : index.getPageStore().getPageSize();
int rowLength = startNext - offsets[at];
start -= OFFSET_LENGTH;
if (optimizeUpdate) {
if (writtenData) {
byte[] d = data.getBytes();
int dataStart = offsets[entryCount];
System.arraycopy(d, dataStart, d,
dataStart + rowLength, offsets[at] - dataStart);
Arrays.fill(d, dataStart, dataStart + rowLength, (byte) 0);
}
}
offsets = remove(offsets, entryCount + 1, at);
add(offsets, at, entryCount, rowLength);
rows = remove(rows, entryCount + 1, at);
}
int getEntryCount() {
return entryCount;
}
@Override
PageBtree split(int splitPoint) {
int newPageId = index.getPageStore().allocatePage();
PageBtreeLeaf p2 = PageBtreeLeaf.create(index, newPageId, parentPageId);
for (int i = splitPoint; i < entryCount;) {
p2.addRow(getRow(splitPoint), false);
removeRow(splitPoint);
}
memoryChange();
p2.memoryChange();
return p2;
}
@Override
PageBtreeLeaf getFirstLeaf() {
return this;
}
@Override
PageBtreeLeaf getLastLeaf() {
return this;
}
@Override
SearchRow remove(SearchRow row) {
int at = find(row, false, false, true);
SearchRow delete = getRow(at);
if (index.compareRows(row, delete) != 0 || delete.getKey() != row.getKey()) {
throw DbException.get(ErrorCode.ROW_NOT_FOUND_WHEN_DELETING_1,
index.getSQL() + ": " + row);
}
index.getPageStore().logUndo(this, data);
if (entryCount == 1) {
// the page is now empty
return row;
}
removeRow(at);
memoryChange();
index.getPageStore().update(this);
if (at == entryCount) {
// the last row changed
return getRow(at - 1);
}
// the last row didn't change
return null;
}
@Override
void freeRecursive() {
index.getPageStore().logUndo(this, data);
index.getPageStore().free(getPos());
}
@Override
int getRowCount() {
return entryCount;
}
@Override
void setRowCountStored(int rowCount) {
// ignore
}
@Override
public void write() {
writeData();
index.getPageStore().writePage(getPos(), data);
}
private void writeHead() {
data.reset();
data.writeByte((byte) (Page.TYPE_BTREE_LEAF |
(onlyPosition ? 0 : Page.FLAG_LAST)));
data.writeShortInt(0);
data.writeInt(parentPageId);
data.writeVarInt(index.getId());
data.writeShortInt(entryCount); //最开始为0
}
private void writeData() {
if (written) {
return;
}
if (!optimizeUpdate) {
readAllRows();
}
writeHead();
for (int i = 0; i < entryCount; i++) {
data.writeShortInt(offsets[i]);
}
if (!writtenData || !optimizeUpdate) {
for (int i = 0; i < entryCount; i++) {
index.writeRow(data, offsets[i], rows[i], onlyPosition);
}
writtenData = true;
}
written = true;
memoryChange();
}
@Override
void find(PageBtreeCursor cursor, SearchRow first, boolean bigger) {
int i = find(first, bigger, false, false); //这里返回的i怎么会>entryCount
if (i > entryCount) { //什么情况下才会使得i > entryCount?
if (parentPageId == PageBtree.ROOT) {
return;
}
PageBtreeNode next = (PageBtreeNode) index.getPage(parentPageId);
next.find(cursor, first, bigger);
return;
}
cursor.setCurrent(this, i);
}
@Override
void last(PageBtreeCursor cursor) {
cursor.setCurrent(this, entryCount - 1);
}
@Override
void remapChildren() {
// nothing to do
}
/**
* Set the cursor to the first row of the next page.
*
* @param cursor the cursor
*/
void nextPage(PageBtreeCursor cursor) {
if (parentPageId == PageBtree.ROOT) {
cursor.setCurrent(null, 0);
return;
}
PageBtreeNode next = (PageBtreeNode) index.getPage(parentPageId);
next.nextPage(cursor, getPos());
}
/**
* Set the cursor to the last row of the previous page.
*
* @param cursor the cursor
*/
void previousPage(PageBtreeCursor cursor) {
if (parentPageId == PageBtree.ROOT) {
cursor.setCurrent(null, 0);
return;
}
PageBtreeNode next = (PageBtreeNode) index.getPage(parentPageId);
next.previousPage(cursor, getPos());
}
@Override
public String toString() {
return tree();
//return "page[" + getPos() + "] b-tree leaf table:" + index.getId() + " entries:" + entryCount;
}
@Override
public void moveTo(Session session, int newPos) {
PageStore store = index.getPageStore();
readAllRows();
PageBtreeLeaf p2 = PageBtreeLeaf.create(index, newPos, parentPageId);
store.logUndo(this, data);
store.logUndo(p2, null);
p2.rows = rows;
p2.entryCount = entryCount;
p2.offsets = offsets;
p2.onlyPosition = onlyPosition;
p2.parentPageId = parentPageId;
p2.start = start;
store.update(p2);
if (parentPageId == ROOT) { //最顶层的leaf，重新把rootPageId指向newPos
index.setRootPageId(session, newPos);
} else {
//此leaf有父PageBtreeNode
PageBtreeNode p = (PageBtreeNode) store.getPage(parentPageId);
p.moveChild(getPos(), newPos);
}
store.free(getPos());
}
@Override
protected void memoryChange() {
if (!PageBtreeIndex.isMemoryChangeRequired()) {
return;
}
int memory = Constants.MEMORY_PAGE_BTREE + index.getPageStore().getPageSize();
if (rows != null) {
memory += getEntryCount() * (4 + Constants.MEMORY_POINTER);
for (int i = 0; i < entryCount; i++) {
SearchRow r = rows[i];
if (r != null) {
memory += r.getMemory();
}
}
}
index.memoryChange(memory >> 2);
}
// 我加上的
@Override
public String tree(String p) {
StringBuilder s = new StringBuilder(200);
s.append(p + "PageBtreeLeaf {\r\n");
s.append(p + "\t" + "indexId = " + index.getId() + "\r\n");
s.append(p + "\t" + "parentPageId = " + parentPageId + "\r\n");
s.append(p + "\t" + "pageId = " + getPos() + "\r\n");
s.append(p + "\t" + "start = " + start + "\r\n");
s.append(p + "\t" + "offsets = " + PageBtreeNode.stringArray2(offsets, entryCount) + "\r\n");
s.append(p + "\t" + "entryCount = " + entryCount + "\r\n");
s.append(p + "\t" + "rows = " + PageBtreeNode.stringArray(rows, p, entryCount));
s.append(p + "}\r\n");
return s.toString();
}
}