HBASE-9999 Add support for small reverse scan - with new files
git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1573951 13f79535-47bb-0310-9956-ffa450edef68
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nkeywal
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/**
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* Copyright The Apache Software Foundation
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with this
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* work for additional information regarding copyright ownership. The ASF
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* licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package org.apache.hadoop.hbase.client;
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import org.apache.commons.logging.Log;
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import org.apache.commons.logging.LogFactory;
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import org.apache.hadoop.classification.InterfaceAudience;
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import org.apache.hadoop.classification.InterfaceStability;
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import org.apache.hadoop.conf.Configuration;
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import org.apache.hadoop.hbase.Cell;
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import org.apache.hadoop.hbase.HConstants;
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import org.apache.hadoop.hbase.KeyValueUtil;
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import org.apache.hadoop.hbase.TableName;
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import org.apache.hadoop.hbase.util.Bytes;
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import java.io.IOException;
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/**
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* Client scanner for small reversed scan. Generally, only one RPC is called to fetch the
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* scan results, unless the results cross multiple regions or the row count of
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* results exceed the caching.
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* <p/>
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* For small scan, it will get better performance than {@link ReversedClientScanner}
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*/
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@InterfaceAudience.Public
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@InterfaceStability.Evolving
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public class ClientSmallReversedScanner extends ReversedClientScanner {
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private static final Log LOG = LogFactory.getLog(ClientSmallReversedScanner.class);
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private RegionServerCallable<Result[]> smallScanCallable = null;
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private byte[] skipRowOfFirstResult = null;
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/**
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* Create a new ReversibleClientScanner for the specified table Note that the
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* passed {@link org.apache.hadoop.hbase.client.Scan}'s start row maybe changed.
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*
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* @param conf The {@link org.apache.hadoop.conf.Configuration} to use.
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* @param scan {@link org.apache.hadoop.hbase.client.Scan} to use in this scanner
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* @param tableName The table that we wish to scan
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* @param connection Connection identifying the cluster
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* @throws java.io.IOException
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*/
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public ClientSmallReversedScanner(Configuration conf, Scan scan, TableName tableName,
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HConnection connection) throws IOException {
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super(conf, scan, tableName, connection);
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}
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/**
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* Gets a scanner for following scan. Move to next region or continue from the
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* last result or start from the start row.
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*
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* @param nbRows
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* @param done true if Server-side says we're done scanning.
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* @param currentRegionDone true if scan is over on current region
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* @return true if has next scanner
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* @throws IOException
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*/
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private boolean nextScanner(int nbRows, final boolean done,
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boolean currentRegionDone) throws IOException {
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// Where to start the next getter
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byte[] localStartKey;
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int cacheNum = nbRows;
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skipRowOfFirstResult = null;
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// if we're at end of table, close and return false to stop iterating
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if (this.currentRegion != null && currentRegionDone) {
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byte[] startKey = this.currentRegion.getStartKey();
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if (startKey == null
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|| Bytes.equals(startKey, HConstants.EMPTY_BYTE_ARRAY)
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|| checkScanStopRow(startKey) || done) {
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close();
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if (LOG.isDebugEnabled()) {
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LOG.debug("Finished with small scan at " + this.currentRegion);
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}
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return false;
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}
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// We take the row just under to get to the previous region.
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localStartKey = createClosestRowBefore(startKey);
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if (LOG.isDebugEnabled()) {
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LOG.debug("Finished with region " + this.currentRegion);
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}
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} else if (this.lastResult != null) {
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localStartKey = this.lastResult.getRow();
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skipRowOfFirstResult = this.lastResult.getRow();
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cacheNum++;
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} else {
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localStartKey = this.scan.getStartRow();
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}
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if (LOG.isTraceEnabled()) {
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LOG.trace("Advancing internal small scanner to startKey at '"
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+ Bytes.toStringBinary(localStartKey) + "'");
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}
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smallScanCallable = ClientSmallScanner.getSmallScanCallable(
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scan, getConnection(), getTable(), localStartKey, cacheNum);
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if (this.scanMetrics != null && skipRowOfFirstResult == null) {
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this.scanMetrics.countOfRegions.incrementAndGet();
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}
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return true;
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}
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@Override
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public Result next() throws IOException {
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// If the scanner is closed and there's nothing left in the cache, next is a
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// no-op.
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if (cache.size() == 0 && this.closed) {
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return null;
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}
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if (cache.size() == 0) {
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Result[] values = null;
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long remainingResultSize = maxScannerResultSize;
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int countdown = this.caching;
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boolean currentRegionDone = false;
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// Values == null means server-side filter has determined we must STOP
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while (remainingResultSize > 0 && countdown > 0
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&& nextScanner(countdown, values == null, currentRegionDone)) {
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// Server returns a null values if scanning is to stop. Else,
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// returns an empty array if scanning is to go on and we've just
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// exhausted current region.
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values = this.caller.callWithRetries(smallScanCallable, scannerTimeout);
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this.currentRegion = smallScanCallable.getHRegionInfo();
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long currentTime = System.currentTimeMillis();
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if (this.scanMetrics != null) {
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this.scanMetrics.sumOfMillisSecBetweenNexts.addAndGet(currentTime
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- lastNext);
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}
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lastNext = currentTime;
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if (values != null && values.length > 0) {
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for (int i = 0; i < values.length; i++) {
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Result rs = values[i];
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if (i == 0 && this.skipRowOfFirstResult != null
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&& Bytes.equals(skipRowOfFirstResult, rs.getRow())) {
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// Skip the first result
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continue;
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}
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cache.add(rs);
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for (Cell kv : rs.rawCells()) {
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remainingResultSize -= KeyValueUtil.ensureKeyValue(kv).heapSize();
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}
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countdown--;
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this.lastResult = rs;
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}
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}
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currentRegionDone = countdown > 0;
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}
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}
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if (cache.size() > 0) {
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return cache.poll();
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}
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// if we exhausted this scanner before calling close, write out the scan
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// metrics
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writeScanMetrics();
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return null;
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}
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@Override
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protected void initializeScannerInConstruction() throws IOException {
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// No need to initialize the scanner when constructing instance, do it when
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// calling next(). Do nothing here.
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}
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@Override
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public void close() {
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if (!scanMetricsPublished) writeScanMetrics();
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closed = true;
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}
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}
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