/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.command;
import java.sql.SQLException;
import java.util.ArrayList;
import org.h2.constant.ErrorCode;
import org.h2.engine.Constants;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.expression.ParameterInterface;
import org.h2.message.DbException;
import org.h2.message.Trace;
import org.h2.result.ResultInterface;
import org.h2.util.MathUtils;
/**
* Represents a SQL statement. This object is only used on the server side.
*/
public abstract class Command implements CommandInterface {
/**
* The session.
*/
protected final Session session;
/**
* The last start time.
*/
protected long startTime;
/**
* The trace module.
*/
private final Trace trace;
/**
* If this query was canceled.
*/
private volatile boolean cancel;
private final String sql;
private boolean canReuse;
Command(Parser parser, String sql) {
this.session = parser.getSession();
this.sql = sql;
trace = session.getDatabase().getTrace(Trace.COMMAND);
}
/**
* Check if this command is transactional.
* If it is not, then it forces the current transaction to commit.
*
* @return true if it is
*/
public abstract boolean isTransactional();
/**
* Check if this command is a query.
*
* @return true if it is
*/
public abstract boolean isQuery();
/**
* Get the list of parameters.
*
* @return the list of parameters
*/
public abstract ArrayList<? extends ParameterInterface> getParameters();
/**
* Check if this command is read only.
*
* @return true if it is
*/
public abstract boolean isReadOnly();
/**
* Get an empty result set containing the meta data.
*
* @return an empty result set
*/
public abstract ResultInterface queryMeta();
/**
* Execute an updating statement, if this is possible.
*
* @return the update count
* @throws DbException if the command is not an updating statement
*/
public int update() {
throw DbException.get(ErrorCode.METHOD_NOT_ALLOWED_FOR_QUERY);
}
/**
* Execute a query statement, if this is possible.
*
* @param maxrows the maximum number of rows returned
* @return the local result set
* @throws DbException if the command is not a query
*/
public ResultInterface query(int maxrows) {
throw DbException.get(ErrorCode.METHOD_ONLY_ALLOWED_FOR_QUERY);
}
public final ResultInterface getMetaData() {
return queryMeta();
}
/**
* Start the stopwatch.
*/
void start() {
if (trace.isInfoEnabled()) {
startTime = System.currentTimeMillis();
}
}
void setProgress(int state) {
session.getDatabase().setProgress(state, sql, 0, 0);
}
/**
* Check if this command has been canceled, and throw an exception if yes.
*
* @throws DbException if the statement has been canceled
*/
protected void checkCanceled() {
if (cancel) {
cancel = false;
throw DbException.get(ErrorCode.STATEMENT_WAS_CANCELED);
}
}
private void stop() {
session.closeTemporaryResults();
session.setCurrentCommand(null);
if (!isTransactional()) {
session.commit(true);
} else if (session.getAutoCommit()) {
session.commit(false);
} else if (session.getDatabase().isMultiThreaded()) {
Database db = session.getDatabase();
if (db != null) {
if (db.getLockMode() == Constants.LOCK_MODE_READ_COMMITTED) {
session.unlockReadLocks();
}
}
}
if (trace.isInfoEnabled() && startTime > 0) {
long time = System.currentTimeMillis() - startTime;
if (time > Constants.SLOW_QUERY_LIMIT_MS) {
trace.info("slow query: {0} ms", time);
}
}
}
/**
* Execute a query and return the result.
* This method prepares everything and calls {@link #query(int)} finally.
*
* @param maxrows the maximum number of rows to return
* @param scrollable if the result set must be scrollable (ignored)
* @return the result set
*/
public ResultInterface executeQuery(int maxrows, boolean scrollable) {
startTime = 0;
long start = 0;
Database database = session.getDatabase();
Object sync = database.isMultiThreaded() ? (Object) session : (Object) database;
session.waitIfExclusiveModeEnabled();
boolean writing = !isReadOnly();
if (writing) {
while (!database.beforeWriting()) {
// wait
}
}
synchronized (sync) {
session.setCurrentCommand(this);
try {
while (true) {
database.checkPowerOff();
try {
return query(maxrows);
} catch (DbException e) {
start = filterConcurrentUpdate(e, start);
} catch (Throwable e) {
throw DbException.convert(e);
}
}
} catch (DbException e) {
e.addSQL(sql);
database.exceptionThrown(e.getSQLException(), sql);
throw e;
} finally {
stop();
if (writing) {
database.afterWriting();
}
}
}
}
public int executeUpdate() {
long start = 0;
Database database = session.getDatabase();
Object sync = database.isMultiThreaded() ? (Object) session : (Object) database;
session.waitIfExclusiveModeEnabled();
boolean callStop = true;
boolean writing = !isReadOnly();
if (writing) {
while (!database.beforeWriting()) {
// wait
}
}
synchronized (sync) {
int rollback = session.getUndoLogPos();
session.setCurrentCommand(this);
try {
while (true) {
database.checkPowerOff();
try {
return update();
} catch (DbException e) {
start = filterConcurrentUpdate(e, start);
} catch (Throwable e) {
throw DbException.convert(e);
}
}
} catch (DbException e) {
e = e.addSQL(sql);
SQLException s = e.getSQLException();
database.exceptionThrown(s, sql);
database.checkPowerOff();
if (s.getErrorCode() == ErrorCode.DEADLOCK_1) {
session.rollback();
} else if (s.getErrorCode() == ErrorCode.OUT_OF_MEMORY) {
// there is a serious problem:
// the transaction may be applied partially
// in this case we need to panic:
// close the database
callStop = false;
database.shutdownImmediately();
throw e;
} else {
session.rollbackTo(rollback, false);
}
throw e;
} finally {
try {
if (callStop) {
stop();
}
} finally {
if (writing) {
database.afterWriting();
}
}
}
}
}
private long filterConcurrentUpdate(DbException e, long start) {
if (e.getErrorCode() != ErrorCode.CONCURRENT_UPDATE_1) {
throw e;
}
long now = System.nanoTime() / 1000000;
if (start != 0 && now - start > session.getLockTimeout()) {
throw DbException.get(ErrorCode.LOCK_TIMEOUT_1, e.getCause(), "");
}
Database database = session.getDatabase();
int sleep = 1 + MathUtils.randomInt(10);
while (true) {
try {
if (database.isMultiThreaded()) {
Thread.sleep(sleep);
} else {
database.wait(sleep);
}
} catch (InterruptedException e1) {
// ignore
}
long slept = System.nanoTime() / 1000000 - now;
if (slept >= sleep) {
break;
}
}
return start == 0 ? now : start;
}
public void close() {
canReuse = true;
}
public void cancel() {
this.cancel = true;
}
public String toString() {
return sql + Trace.formatParams(getParameters());
}
public boolean isCacheable() {
return false;
}
/**
* Whether the command is already closed (in which case it can be re-used).
*
* @return true if it can be re-used
*/
public boolean canReuse() {
return canReuse;
}
/**
* The command is now re-used, therefore reset the canReuse flag, and the
* parameter values.
*/
public void reuse() {
canReuse = false;
ArrayList<? extends ParameterInterface> parameters = getParameters();
for (int i = 0, size = parameters.size(); i < size; i++) {
ParameterInterface param = parameters.get(i);
param.setValue(null, true);
}
}
}