/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.client;
import java.io.IOException;
import java.util.ArrayList;
import java.util.LinkedList;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.DoNotRetryIOException;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.NotServingRegionException;
import org.apache.hadoop.hbase.OutOfOrderScannerNextException;
import org.apache.hadoop.hbase.UnknownScannerException;
import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
import org.apache.hadoop.hbase.regionserver.RegionServerStoppedException;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.DataOutputBuffer;
/**
* Implements the scanner interface for the HBase client.
* If there are multiple regions in a table, this scanner will iterate
* through them all.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ClientScanner extends AbstractClientScanner {
private final Log LOG = LogFactory.getLog(this.getClass());
private Scan scan;
private boolean closed = false;
// Current region scanner is against. Gets cleared if current region goes
// wonky: e.g. if it splits on us.
private HRegionInfo currentRegion = null;
private ScannerCallable callable = null;
private final LinkedList<Result> cache = new LinkedList<Result>();
private final int caching;
private long lastNext;
// Keep lastResult returned successfully in case we have to reset scanner.
private Result lastResult = null;
private ScanMetrics scanMetrics = null;
private final long maxScannerResultSize;
private final HConnection connection;
private final byte[] tableName;
private final int scannerTimeout;
/**
* Create a new ClientScanner for the specified table. An HConnection will be
* retrieved using the passed Configuration.
* Note that the passed {@link Scan}'s start row maybe changed changed.
*
* @param conf The {@link Configuration} to use.
* @param scan {@link Scan} to use in this scanner
* @param tableName The table that we wish to scan
* @throws IOException
*/
public ClientScanner(final Configuration conf, final Scan scan,
final byte[] tableName) throws IOException {
this(conf, scan, tableName, HConnectionManager.getConnection(conf));
}
/**
* Create a new ClientScanner for the specified table
* Note that the passed {@link Scan}'s start row maybe changed changed.
*
* @param conf The {@link Configuration} to use.
* @param scan {@link Scan} to use in this scanner
* @param tableName The table that we wish to scan
* @param connection Connection identifying the cluster
* @throws IOException
*/
public ClientScanner(final Configuration conf, final Scan scan,
final byte[] tableName, HConnection connection) throws IOException {
if (LOG.isDebugEnabled()) {
LOG.debug("Creating scanner over "
+ Bytes.toString(tableName)
+ " starting at key '" + Bytes.toStringBinary(scan.getStartRow()) + "'");
}
this.scan = scan;
this.tableName = tableName;
this.lastNext = System.currentTimeMillis();
this.connection = connection;
if (scan.getMaxResultSize() > 0) {
this.maxScannerResultSize = scan.getMaxResultSize();
} else {
this.maxScannerResultSize = conf.getLong(
HConstants.HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE_KEY,
HConstants.DEFAULT_HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE);
}
this.scannerTimeout = conf.getInt(HConstants.HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD,
HConstants.DEFAULT_HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD);
// check if application wants to collect scan metrics
byte[] enableMetrics = scan.getAttribute(
Scan.SCAN_ATTRIBUTES_METRICS_ENABLE);
if (enableMetrics != null && Bytes.toBoolean(enableMetrics)) {
scanMetrics = new ScanMetrics();
}
// Use the caching from the Scan. If not set, use the default cache setting for this table.
if (this.scan.getCaching() > 0) {
this.caching = this.scan.getCaching();
} else {
this.caching = conf.getInt("hbase.client.scanner.caching", 1);
}
// initialize the scanner
nextScanner(this.caching, false);
}
protected HConnection getConnection() {
return this.connection;
}
protected byte[] getTableName() {
return this.tableName;
}
protected Scan getScan() {
return scan;
}
protected long getTimestamp() {
return lastNext;
}
// returns true if the passed region endKey
private boolean checkScanStopRow(final byte [] endKey) {
if (this.scan.getStopRow().length > 0) {
// there is a stop row, check to see if we are past it.
byte [] stopRow = scan.getStopRow();
int cmp = Bytes.compareTo(stopRow, 0, stopRow.length,
endKey, 0, endKey.length);
if (cmp <= 0) {
// stopRow <= endKey (endKey is equals to or larger than stopRow)
// This is a stop.
return true;
}
}
return false; //unlikely.
}
/*
* Gets a scanner for the next region. If this.currentRegion != null, then
* we will move to the endrow of this.currentRegion. Else we will get
* scanner at the scan.getStartRow(). We will go no further, just tidy
* up outstanding scanners, if <code>currentRegion != null</code> and
* <code>done</code> is true.
* @param nbRows
* @param done Server-side says we're done scanning.
*/
private boolean nextScanner(int nbRows, final boolean done)
throws IOException {
// Close the previous scanner if it's open
if (this.callable != null) {
this.callable.setClose();
callable.withRetries();
this.callable = null;
}
// Where to start the next scanner
byte [] localStartKey;
// if we're at end of table, close and return false to stop iterating
if (this.currentRegion != null) {
byte [] endKey = this.currentRegion.getEndKey();
if (endKey == null ||
Bytes.equals(endKey, HConstants.EMPTY_BYTE_ARRAY) ||
checkScanStopRow(endKey) ||
done) {
close();
if (LOG.isDebugEnabled()) {
LOG.debug("Finished with scanning at " + this.currentRegion);
}
return false;
}
localStartKey = endKey;
if (LOG.isDebugEnabled()) {
LOG.debug("Finished with region " + this.currentRegion);
}
} else {
localStartKey = this.scan.getStartRow();
}
if (LOG.isDebugEnabled()) {
LOG.debug("Advancing internal scanner to startKey at '" +
Bytes.toStringBinary(localStartKey) + "'");
}
try {
callable = getScannerCallable(localStartKey, nbRows);
// Open a scanner on the region server starting at the
// beginning of the region
callable.withRetries();
this.currentRegion = callable.getHRegionInfo();
if (this.scanMetrics != null) {
this.scanMetrics.countOfRegions.inc();
}
} catch (IOException e) {
close();
throw e;
}
return true;
}
protected ScannerCallable getScannerCallable(byte [] localStartKey,
int nbRows) {
scan.setStartRow(localStartKey);
ScannerCallable s = new ScannerCallable(getConnection(),
getTableName(), scan, this.scanMetrics);
s.setCaching(nbRows);
return s;
}
/**
* Publish the scan metrics. For now, we use scan.setAttribute to pass the metrics back to the
* application or TableInputFormat.Later, we could push it to other systems. We don't use metrics
* framework because it doesn't support multi-instances of the same metrics on the same machine;
* for scan/map reduce scenarios, we will have multiple scans running at the same time.
*
* By default, scan metrics are disabled; if the application wants to collect them, this behavior
* can be turned on by calling calling:
*
* scan.setAttribute(SCAN_ATTRIBUTES_METRICS_ENABLE, Bytes.toBytes(Boolean.TRUE))
*/
private void writeScanMetrics() throws IOException {
if (this.scanMetrics == null) {
return;
}
final DataOutputBuffer d = new DataOutputBuffer();
scanMetrics.write(d);
scan.setAttribute(Scan.SCAN_ATTRIBUTES_METRICS_DATA, d.getData());
}
public Result next() throws IOException {
// If the scanner is closed and there's nothing left in the cache, next is a no-op.
if (cache.size() == 0 && this.closed) {
return null;
}
if (cache.size() == 0) {
Result [] values = null;
long remainingResultSize = maxScannerResultSize;
int countdown = this.caching;
// We need to reset it if it's a new callable that was created
// with a countdown in nextScanner
callable.setCaching(this.caching);
// This flag is set when we want to skip the result returned. We do
// this when we reset scanner because it split under us.
boolean skipFirst = false;
boolean retryAfterOutOfOrderException = true;
do {
try {
if (skipFirst) {
// Skip only the first row (which was the last row of the last
// already-processed batch).
callable.setCaching(1);
values = callable.withRetries();
callable.setCaching(this.caching);
skipFirst = false;
}
// Server returns a null values if scanning is to stop. Else,
// returns an empty array if scanning is to go on and we've just
// exhausted current region.
values = callable.withRetries();
retryAfterOutOfOrderException = true;
} catch (DoNotRetryIOException e) {
if (e instanceof UnknownScannerException) {
long timeout = lastNext + scannerTimeout;
// If we are over the timeout, throw this exception to the client
// Else, it's because the region moved and we used the old id
// against the new region server; reset the scanner.
if (timeout < System.currentTimeMillis()) {
long elapsed = System.currentTimeMillis() - lastNext;
ScannerTimeoutException ex = new ScannerTimeoutException(
elapsed + "ms passed since the last invocation, " +
"timeout is currently set to " + scannerTimeout);
ex.initCause(e);
throw ex;
}
} else {
Throwable cause = e.getCause();
if ((cause == null || (!(cause instanceof NotServingRegionException)
&& !(cause instanceof RegionServerStoppedException)))
&& !(e instanceof OutOfOrderScannerNextException)) {
throw e;
}
}
// Else, its signal from depths of ScannerCallable that we got an
// NSRE on a next and that we need to reset the scanner.
if (this.lastResult != null) {
this.scan.setStartRow(this.lastResult.getRow());
// Skip first row returned. We already let it out on previous
// invocation.
skipFirst = true;
}
if (e instanceof OutOfOrderScannerNextException) {
if (retryAfterOutOfOrderException) {
retryAfterOutOfOrderException = false;
} else {
throw new DoNotRetryIOException("Failed after retry"
+ ", it could be cause by rpc timeout", e);
}
}
// Clear region
this.currentRegion = null;
callable = null;
continue;
}
long currentTime = System.currentTimeMillis();
if (this.scanMetrics != null ) {
this.scanMetrics.sumOfMillisSecBetweenNexts.inc(currentTime-lastNext);
}
lastNext = currentTime;
if (values != null && values.length > 0) {
for (Result rs : values) {
cache.add(rs);
for (KeyValue kv : rs.raw()) {
remainingResultSize -= kv.heapSize();
}
countdown--;
this.lastResult = rs;
}
}
// Values == null means server-side filter has determined we must STOP
} while (remainingResultSize > 0 && countdown > 0 && nextScanner(countdown, values == null));
}
if (cache.size() > 0) {
return cache.poll();
}
// if we exhausted this scanner before calling close, write out the scan metrics
writeScanMetrics();
return null;
}
/**
* Get <param>nbRows</param> rows.
* How many RPCs are made is determined by the {@link Scan#setCaching(int)}
* setting (or hbase.client.scanner.caching in hbase-site.xml).
* @param nbRows number of rows to return
* @return Between zero and <param>nbRows</param> RowResults. Scan is done
* if returned array is of zero-length (We never return null).
* @throws IOException
*/
public Result [] next(int nbRows) throws IOException {
// Collect values to be returned here
ArrayList<Result> resultSets = new ArrayList<Result>(nbRows);
for(int i = 0; i < nbRows; i++) {
Result next = next();
if (next != null) {
resultSets.add(next);
} else {
break;
}
}
return resultSets.toArray(new Result[resultSets.size()]);
}
public void close() {
if (callable != null) {
callable.setClose();
try {
callable.withRetries();
} catch (IOException e) {
// We used to catch this error, interpret, and rethrow. However, we
// have since decided that it's not nice for a scanner's close to
// throw exceptions. Chances are it was just an UnknownScanner
// exception due to lease time out.
} finally {
// we want to output the scan metrics even if an error occurred on close
try {
writeScanMetrics();
} catch (IOException e) {
// As above, we still don't want the scanner close() method to throw.
}
}
callable = null;
}
closed = true;
}
}