org.h2.index.MultiVersionCursor Maven / Gradle / Ivy
/*
* 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 org.h2.engine.Session;
import org.h2.engine.SysProperties;
import org.h2.message.DbException;
import org.h2.result.Row;
import org.h2.result.SearchRow;
import org.h2.util.MathUtils;
/**
* The cursor implementation for the multi-version index.
*/
public class MultiVersionCursor implements Cursor {
private final MultiVersionIndex index;
private final Session session;
private final Cursor baseCursor, deltaCursor;
private final Object sync;
private SearchRow baseRow;
private Row deltaRow;
private boolean onBase;
private boolean end;
private boolean needNewDelta, needNewBase;
private boolean reverse;
MultiVersionCursor(Session session, MultiVersionIndex index, Cursor base,
Cursor delta, Object sync) {
this.session = session;
this.index = index;
this.baseCursor = base;
this.deltaCursor = delta;
this.sync = sync;
needNewDelta = true;
needNewBase = true;
}
/**
* Load the current row.
*/
void loadCurrent() {
synchronized (sync) {
baseRow = baseCursor.getSearchRow();
deltaRow = deltaCursor.get();
needNewDelta = false;
needNewBase = false;
}
}
private void loadNext(boolean base) {
synchronized (sync) {
if (base) {
if (step(baseCursor)) {
baseRow = baseCursor.getSearchRow();
} else {
baseRow = null;
}
} else {
if (step(deltaCursor)) {
deltaRow = deltaCursor.get();
} else {
deltaRow = null;
}
}
}
}
private boolean step(Cursor cursor) {
return reverse ? cursor.previous() : cursor.next();
}
@Override
public Row get() {
synchronized (sync) {
if (end) {
return null;
}
return onBase ? baseCursor.get() : deltaCursor.get();
}
}
@Override
public SearchRow getSearchRow() {
synchronized (sync) {
if (end) {
return null;
}
return onBase ? baseCursor.getSearchRow() : deltaCursor.getSearchRow();
}
}
@Override
public boolean next() {
synchronized (sync) {
if (SysProperties.CHECK && end) {
DbException.throwInternalError();
}
while (true) {
if (needNewDelta) {
loadNext(false);
needNewDelta = false;
}
if (needNewBase) {
loadNext(true);
needNewBase = false;
}
if (deltaRow == null) {
if (baseRow == null) {
end = true;
return false;
}
onBase = true;
needNewBase = true;
return true;
}
int sessionId = deltaRow.getSessionId();
boolean isThisSession = sessionId == session.getId();
boolean isDeleted = deltaRow.isDeleted();
if (isThisSession && isDeleted) {
needNewDelta = true;
continue;
}
if (baseRow == null) {
if (isDeleted) {
if (isThisSession) {
end = true;
return false;
}
// the row was deleted by another session: return it
onBase = false;
needNewDelta = true;
return true;
}
DbException.throwInternalError();
}
int compare = index.compareRows(deltaRow, baseRow);
if (compare == 0) {
// can't use compareKeys because the
// version would be compared as well
long k1 = deltaRow.getKey();
long k2 = baseRow.getKey();
compare = MathUtils.compareLong(k1, k2);
}
if (compare == 0) {
if (isDeleted) {
if (isThisSession) {
DbException.throwInternalError();
}
// another session updated the row
} else {
if (isThisSession) {
onBase = false;
needNewBase = true;
needNewDelta = true;
return true;
}
// another session inserted the row: ignore
needNewBase = true;
needNewDelta = true;
continue;
}
}
if (compare > 0) {
onBase = true;
needNewBase = true;
return true;
}
onBase = false;
needNewDelta = true;
return true;
}
}
}
@Override
public boolean previous() {
reverse = true;
try {
return next();
} finally {
reverse = false;
}
}
}