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/**
*
* 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.regionserver;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.ArrayList;
import java.util.List;
import java.util.NavigableSet;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.DoNotRetryIOException;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.KeyValue.KVComparator;
import org.apache.hadoop.hbase.KeyValueUtil;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.client.IsolationLevel;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.executor.ExecutorService;
import org.apache.hadoop.hbase.filter.Filter;
import org.apache.hadoop.hbase.regionserver.ScannerContext.LimitScope;
import org.apache.hadoop.hbase.regionserver.ScannerContext.NextState;
import org.apache.hadoop.hbase.regionserver.handler.ParallelSeekHandler;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import com.google.common.annotations.VisibleForTesting;
import org.apache.hadoop.hbase.util.CollectionUtils;
/**
* Scanner scans both the memstore and the Store. Coalesce KeyValue stream
* into List<KeyValue> for a single row.
*/
@InterfaceAudience.Private
public class StoreScanner extends NonReversedNonLazyKeyValueScanner
implements KeyValueScanner, InternalScanner, ChangedReadersObserver {
private static final Log LOG = LogFactory.getLog(StoreScanner.class);
// In unit tests, the store could be null
protected final Store store;
protected ScanQueryMatcher matcher;
protected KeyValueHeap heap;
protected boolean cacheBlocks;
protected long countPerRow = 0;
protected int storeLimit = -1;
protected int storeOffset = 0;
// Used to indicate that the scanner has closed (see HBASE-1107)
// Doesnt need to be volatile because it's always accessed via synchronized methods
protected boolean closing = false;
protected final boolean get;
protected final boolean explicitColumnQuery;
protected final boolean useRowColBloom;
/**
* A flag that enables StoreFileScanner parallel-seeking
*/
protected boolean parallelSeekEnabled = false;
protected ExecutorService executor;
protected final Scan scan;
protected final NavigableSet columns;
protected final long oldestUnexpiredTS;
protected final long now;
protected final int minVersions;
protected final long maxRowSize;
protected final long cellsPerHeartbeatCheck;
/**
* If we close the memstore scanners before sending data to client, the chunk may be reclaimed
* by other updates and the data will be corrupt.
*/
private final List scannersForDelayedClose = new ArrayList<>();
/**
* The number of KVs seen by the scanner. Includes explicitly skipped KVs, but not
* KVs skipped via seeking to next row/column. TODO: estimate them?
*/
private long kvsScanned = 0;
private Cell prevCell = null;
/** We don't ever expect to change this, the constant is just for clarity. */
static final boolean LAZY_SEEK_ENABLED_BY_DEFAULT = true;
public static final String STORESCANNER_PARALLEL_SEEK_ENABLE =
"hbase.storescanner.parallel.seek.enable";
/** Used during unit testing to ensure that lazy seek does save seek ops */
protected static boolean lazySeekEnabledGlobally =
LAZY_SEEK_ENABLED_BY_DEFAULT;
/**
* The number of cells scanned in between timeout checks. Specifying a larger value means that
* timeout checks will occur less frequently. Specifying a small value will lead to more frequent
* timeout checks.
*/
public static final String HBASE_CELLS_SCANNED_PER_HEARTBEAT_CHECK =
"hbase.cells.scanned.per.heartbeat.check";
/**
* Default value of {@link #HBASE_CELLS_SCANNED_PER_HEARTBEAT_CHECK}.
*/
public static final long DEFAULT_HBASE_CELLS_SCANNED_PER_HEARTBEAT_CHECK = 10000;
// if heap == null and lastTop != null, you need to reseek given the key below
protected Cell lastTop = null;
// A flag whether use pread for scan
private boolean scanUsePread = false;
// Indicates whether there was flush during the course of the scan
private volatile boolean flushed = false;
// generally we get one file from a flush
private final List flushedstoreFileScanners =
new ArrayList(1);
// generally we get one memstroe scanner from a flush
private final List memStoreScannersAfterFlush = new ArrayList<>(1);
// The current list of scanners
private final List currentScanners = new ArrayList();
// flush update lock
private ReentrantLock flushLock = new ReentrantLock();
private final long readPt;
private boolean topChanged = false;
// used by the injection framework to test race between StoreScanner construction and compaction
enum StoreScannerCompactionRace {
BEFORE_SEEK,
AFTER_SEEK,
COMPACT_COMPLETE
}
/** An internal constructor. */
protected StoreScanner(Store store, Scan scan, final ScanInfo scanInfo,
final NavigableSet columns, long readPt, boolean cacheBlocks) {
this.readPt = readPt;
this.store = store;
this.cacheBlocks = cacheBlocks;
get = scan.isGetScan();
int numCol = columns == null ? 0 : columns.size();
explicitColumnQuery = numCol > 0;
this.scan = scan;
this.columns = columns;
this.now = EnvironmentEdgeManager.currentTime();
this.oldestUnexpiredTS = now - scanInfo.getTtl();
this.minVersions = scanInfo.getMinVersions();
// We look up row-column Bloom filters for multi-column queries as part of
// the seek operation. However, we also look the row-column Bloom filter
// for multi-row (non-"get") scans because this is not done in
// StoreFile.passesBloomFilter(Scan, SortedSet).
this.useRowColBloom = numCol > 1 || (!get && numCol == 1);
this.maxRowSize = scanInfo.getTableMaxRowSize();
this.scanUsePread = scan.isSmall()? true: scanInfo.isUsePread();
this.cellsPerHeartbeatCheck = scanInfo.getCellsPerTimeoutCheck();
// Parallel seeking is on if the config allows and more there is more than one store file.
if (this.store != null && this.store.getStorefilesCount() > 1) {
RegionServerServices rsService = ((HStore)store).getHRegion().getRegionServerServices();
if (rsService != null && scanInfo.isParallelSeekEnabled()) {
this.parallelSeekEnabled = true;
this.executor = rsService.getExecutorService();
}
}
}
protected void addCurrentScanners(List scanners) {
this.currentScanners.addAll(scanners);
}
/**
* Opens a scanner across memstore, snapshot, and all StoreFiles. Assumes we
* are not in a compaction.
*
* @param store who we scan
* @param scan the spec
* @param columns which columns we are scanning
* @throws IOException
*/
public StoreScanner(Store store, ScanInfo scanInfo, Scan scan, final NavigableSet columns,
long readPt)
throws IOException {
this(store, scan, scanInfo, columns, readPt, scan.getCacheBlocks());
if (columns != null && scan.isRaw()) {
throw new DoNotRetryIOException("Cannot specify any column for a raw scan");
}
matcher = new ScanQueryMatcher(scan, scanInfo, columns,
ScanType.USER_SCAN, Long.MAX_VALUE, HConstants.LATEST_TIMESTAMP,
oldestUnexpiredTS, now, store.getCoprocessorHost());
this.store.addChangedReaderObserver(this);
try {
// Pass columns to try to filter out unnecessary StoreFiles.
List scanners = getScannersNoCompaction();
// Seek all scanners to the start of the Row (or if the exact matching row
// key does not exist, then to the start of the next matching Row).
// Always check bloom filter to optimize the top row seek for delete
// family marker.
seekScanners(scanners, matcher.getStartKey(), explicitColumnQuery && lazySeekEnabledGlobally,
parallelSeekEnabled);
// set storeLimit
this.storeLimit = scan.getMaxResultsPerColumnFamily();
// set rowOffset
this.storeOffset = scan.getRowOffsetPerColumnFamily();
addCurrentScanners(scanners);
// Combine all seeked scanners with a heap
resetKVHeap(scanners, store.getComparator());
} catch (IOException e) {
// remove us from the HStore#changedReaderObservers here or we'll have no chance to
// and might cause memory leak
this.store.deleteChangedReaderObserver(this);
throw e;
}
}
/**
* Used for compactions.
*
* Opens a scanner across specified StoreFiles.
* @param store who we scan
* @param scan the spec
* @param scanners ancillary scanners
* @param smallestReadPoint the readPoint that we should use for tracking
* versions
*/
public StoreScanner(Store store, ScanInfo scanInfo, Scan scan,
List scanners, ScanType scanType,
long smallestReadPoint, long earliestPutTs) throws IOException {
this(store, scanInfo, scan, scanners, scanType, smallestReadPoint, earliestPutTs, null, null);
}
/**
* Used for compactions that drop deletes from a limited range of rows.
*
* Opens a scanner across specified StoreFiles.
* @param store who we scan
* @param scan the spec
* @param scanners ancillary scanners
* @param smallestReadPoint the readPoint that we should use for tracking versions
* @param dropDeletesFromRow The inclusive left bound of the range; can be EMPTY_START_ROW.
* @param dropDeletesToRow The exclusive right bound of the range; can be EMPTY_END_ROW.
*/
public StoreScanner(Store store, ScanInfo scanInfo, Scan scan,
List scanners, long smallestReadPoint, long earliestPutTs,
byte[] dropDeletesFromRow, byte[] dropDeletesToRow) throws IOException {
this(store, scanInfo, scan, scanners, ScanType.COMPACT_RETAIN_DELETES, smallestReadPoint,
earliestPutTs, dropDeletesFromRow, dropDeletesToRow);
}
private StoreScanner(Store store, ScanInfo scanInfo, Scan scan,
List scanners, ScanType scanType, long smallestReadPoint,
long earliestPutTs, byte[] dropDeletesFromRow, byte[] dropDeletesToRow) throws IOException {
this(store, scan, scanInfo, null,
((HStore)store).getHRegion().getReadpoint(IsolationLevel.READ_COMMITTED), false);
if (dropDeletesFromRow == null) {
matcher = new ScanQueryMatcher(scan, scanInfo, null, scanType, smallestReadPoint,
earliestPutTs, oldestUnexpiredTS, now, store.getCoprocessorHost());
} else {
matcher = new ScanQueryMatcher(scan, scanInfo, null, smallestReadPoint, earliestPutTs,
oldestUnexpiredTS, now, dropDeletesFromRow, dropDeletesToRow, store.getCoprocessorHost());
}
// Filter the list of scanners using Bloom filters, time range, TTL, etc.
scanners = selectScannersFrom(scanners);
// Seek all scanners to the initial key
seekScanners(scanners, matcher.getStartKey(), false, parallelSeekEnabled);
addCurrentScanners(scanners);
// Combine all seeked scanners with a heap
resetKVHeap(scanners, store.getComparator());
}
@VisibleForTesting
StoreScanner(final Scan scan, ScanInfo scanInfo,
ScanType scanType, final NavigableSet columns,
final List scanners) throws IOException {
this(scan, scanInfo, scanType, columns, scanners,
HConstants.LATEST_TIMESTAMP,
// 0 is passed as readpoint because the test bypasses Store
0);
}
@VisibleForTesting
StoreScanner(final Scan scan, ScanInfo scanInfo,
ScanType scanType, final NavigableSet columns,
final List scanners, long earliestPutTs)
throws IOException {
this(scan, scanInfo, scanType, columns, scanners, earliestPutTs,
// 0 is passed as readpoint because the test bypasses Store
0);
}
private StoreScanner(final Scan scan, ScanInfo scanInfo,
ScanType scanType, final NavigableSet columns,
final List scanners, long earliestPutTs, long readPt)
throws IOException {
this(null, scan, scanInfo, columns, readPt, scan.getCacheBlocks());
this.matcher = new ScanQueryMatcher(scan, scanInfo, columns, scanType,
Long.MAX_VALUE, earliestPutTs, oldestUnexpiredTS, now, null);
// In unit tests, the store could be null
if (this.store != null) {
this.store.addChangedReaderObserver(this);
}
// Seek all scanners to the initial key
seekScanners(scanners, matcher.getStartKey(), false, parallelSeekEnabled);
addCurrentScanners(scanners);
resetKVHeap(scanners, scanInfo.getComparator());
}
/**
* Get a filtered list of scanners. Assumes we are not in a compaction.
* @return list of scanners to seek
*/
protected List getScannersNoCompaction() throws IOException {
final boolean isCompaction = false;
boolean usePread = get || scanUsePread;
return selectScannersFrom(store.getScanners(cacheBlocks, get, usePread,
isCompaction, matcher, scan.getStartRow(), scan.getStopRow(), this.readPt));
}
/**
* Seek the specified scanners with the given key
* @param scanners
* @param seekKey
* @param isLazy true if using lazy seek
* @param isParallelSeek true if using parallel seek
* @throws IOException
*/
protected void seekScanners(List scanners,
Cell seekKey, boolean isLazy, boolean isParallelSeek)
throws IOException {
// Seek all scanners to the start of the Row (or if the exact matching row
// key does not exist, then to the start of the next matching Row).
// Always check bloom filter to optimize the top row seek for delete
// family marker.
if (isLazy) {
for (KeyValueScanner scanner : scanners) {
scanner.requestSeek(seekKey, false, true);
}
} else {
if (!isParallelSeek) {
long totalScannersSoughtBytes = 0;
for (KeyValueScanner scanner : scanners) {
if (totalScannersSoughtBytes >= maxRowSize) {
throw new RowTooBigException("Max row size allowed: " + maxRowSize
+ ", but row is bigger than that");
}
scanner.seek(seekKey);
Cell c = scanner.peek();
if (c != null) {
totalScannersSoughtBytes += CellUtil.estimatedSerializedSizeOf(c);
}
}
} else {
parallelSeek(scanners, seekKey);
}
}
}
protected void resetKVHeap(List scanners,
KVComparator comparator) throws IOException {
// Combine all seeked scanners with a heap
heap = new KeyValueHeap(scanners, comparator);
}
/**
* Filters the given list of scanners using Bloom filter, time range, and
* TTL.
*/
protected List selectScannersFrom(
final List allScanners) {
boolean memOnly;
boolean filesOnly;
if (scan instanceof InternalScan) {
InternalScan iscan = (InternalScan)scan;
memOnly = iscan.isCheckOnlyMemStore();
filesOnly = iscan.isCheckOnlyStoreFiles();
} else {
memOnly = false;
filesOnly = false;
}
List scanners =
new ArrayList(allScanners.size());
// We can only exclude store files based on TTL if minVersions is set to 0.
// Otherwise, we might have to return KVs that have technically expired.
long expiredTimestampCutoff = minVersions == 0 ? oldestUnexpiredTS: Long.MIN_VALUE;
// include only those scan files which pass all filters
for (KeyValueScanner kvs : allScanners) {
boolean isFile = kvs.isFileScanner();
if ((!isFile && filesOnly) || (isFile && memOnly)) {
continue;
}
if (kvs.shouldUseScanner(scan, store, expiredTimestampCutoff)) {
scanners.add(kvs);
} else {
kvs.close();
}
}
return scanners;
}
@Override
public Cell peek() {
if (this.heap == null) {
return this.lastTop;
}
return this.heap.peek();
}
@Override
public KeyValue next() {
// throw runtime exception perhaps?
throw new RuntimeException("Never call StoreScanner.next()");
}
@Override
public void close() {
if (this.closing) {
return;
}
// Lets remove from observers as early as possible
// Under test, we dont have a this.store
if (this.store != null) {
this.store.deleteChangedReaderObserver(this);
}
// There is a race condition between close() and updateReaders(), during region flush. So,
// even though its just close, we will still acquire the flush lock, as a
// ConcurrentModificationException will abort the regionserver.
flushLock.lock();
try {
this.closing = true;
clearAndClose(scannersForDelayedClose);
clearAndClose(memStoreScannersAfterFlush);
// clear them at any case. In case scanner.next() was never called
// and there were some lease expiry we need to close all the scanners
// on the flushed files which are open
clearAndClose(flushedstoreFileScanners);
} finally {
flushLock.unlock();
}
if (this.heap != null)
this.heap.close();
this.heap = null; // CLOSED!
this.lastTop = null; // If both are null, we are closed.
}
@Override
public boolean seek(Cell key) throws IOException {
boolean flushed = checkFlushed();
// reset matcher state, in case that underlying store changed
checkReseek(flushed);
return this.heap.seek(key);
}
@Override
public boolean next(List outResult) throws IOException {
return next(outResult, NoLimitScannerContext.getInstance());
}
/**
* Get the next row of values from this Store.
* @param outResult
* @param scannerContext
* @return true if there are more rows, false if scanner is done
*/
@Override
public boolean next(List outResult, ScannerContext scannerContext) throws IOException {
if (scannerContext == null) {
throw new IllegalArgumentException("Scanner context cannot be null");
}
boolean flushed = checkFlushed();
if (checkReseek(flushed)) {
return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
}
// if the heap was left null, then the scanners had previously run out anyways, close and
// return.
if (this.heap == null) {
close();
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
Cell cell = this.heap.peek();
if (cell == null) {
close();
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
// only call setRow if the row changes; avoids confusing the query matcher
// if scanning intra-row
byte[] row = cell.getRowArray();
int offset = cell.getRowOffset();
short length = cell.getRowLength();
// If no limits exists in the scope LimitScope.Between_Cells then we are sure we are changing
// rows. Else it is possible we are still traversing the same row so we must perform the row
// comparison.
if (!scannerContext.hasAnyLimit(LimitScope.BETWEEN_CELLS) || matcher.row == null) {
this.countPerRow = 0;
matcher.setRow(row, offset, length);
}
// Clear progress away unless invoker has indicated it should be kept.
if (!scannerContext.getKeepProgress()) scannerContext.clearProgress();
// Only do a sanity-check if store and comparator are available.
KeyValue.KVComparator comparator =
store != null ? store.getComparator() : null;
int count = 0;
long totalBytesRead = 0;
LOOP: do {
// Update and check the time limit based on the configured value of cellsPerTimeoutCheck
if ((kvsScanned % cellsPerHeartbeatCheck == 0)) {
scannerContext.updateTimeProgress();
if (scannerContext.checkTimeLimit(LimitScope.BETWEEN_CELLS)) {
return scannerContext.setScannerState(NextState.TIME_LIMIT_REACHED).hasMoreValues();
}
}
if (prevCell != cell) ++kvsScanned; // Do object compare - we set prevKV from the same heap.
checkScanOrder(prevCell, cell, comparator);
prevCell = cell;
topChanged = false;
ScanQueryMatcher.MatchCode qcode = matcher.match(cell);
switch (qcode) {
case INCLUDE:
case INCLUDE_AND_SEEK_NEXT_ROW:
case INCLUDE_AND_SEEK_NEXT_COL:
Filter f = matcher.getFilter();
if (f != null) {
// TODO convert Scan Query Matcher to be Cell instead of KV based ?
cell = f.transformCell(cell);
}
this.countPerRow++;
if (storeLimit > -1 &&
this.countPerRow > (storeLimit + storeOffset)) {
// do what SEEK_NEXT_ROW does.
if (!matcher.moreRowsMayExistAfter(cell)) {
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
// Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
// the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
// another compareRow to say the current row is DONE
matcher.row = null;
seekToNextRow(cell);
break LOOP;
}
// add to results only if we have skipped #storeOffset kvs
// also update metric accordingly
if (this.countPerRow > storeOffset) {
outResult.add(cell);
// Update local tracking information
count++;
totalBytesRead += CellUtil.estimatedSerializedSizeOf(cell);
// Update the progress of the scanner context
scannerContext.incrementSizeProgress(CellUtil.estimatedHeapSizeOfWithoutTags(cell));
scannerContext.incrementBatchProgress(1);
if (totalBytesRead > maxRowSize) {
throw new RowTooBigException("Max row size allowed: " + maxRowSize
+ ", but the row is bigger than that.");
}
}
if (qcode == ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_ROW) {
if (!matcher.moreRowsMayExistAfter(cell)) {
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
// Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
// the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
// another compareRow to say the current row is DONE
matcher.row = null;
seekOrSkipToNextRow(cell);
} else if (qcode == ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL) {
seekOrSkipToNextColumn(cell);
} else {
this.heap.next();
}
if (scannerContext.checkBatchLimit(LimitScope.BETWEEN_CELLS)) {
break LOOP;
}
if (scannerContext.checkSizeLimit(LimitScope.BETWEEN_CELLS)) {
break LOOP;
}
continue;
case DONE:
// Optimization for Gets! If DONE, no more to get on this row, early exit!
if (this.scan.isGetScan()) {
// Then no more to this row... exit.
close();// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
// We are sure that this row is done and we are in the next row.
// So subsequent StoresScanner.next() call need not do another compare
// and set the matcher.row
matcher.row = null;
return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
case DONE_SCAN:
close();
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
case SEEK_NEXT_ROW:
// This is just a relatively simple end of scan fix, to short-cut end
// us if there is an endKey in the scan.
if (!matcher.moreRowsMayExistAfter(cell)) {
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
// Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
// the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
// another compareRow to say the current row is DONE
matcher.row = null;
seekOrSkipToNextRow(cell);
NextState stateAfterSeekNextRow = needToReturn(outResult);
if (stateAfterSeekNextRow != null) {
return scannerContext.setScannerState(stateAfterSeekNextRow).hasMoreValues();
}
break;
case SEEK_NEXT_COL:
seekOrSkipToNextColumn(cell);
NextState stateAfterSeekNextColumn = needToReturn(outResult);
if (stateAfterSeekNextColumn != null) {
return scannerContext.setScannerState(stateAfterSeekNextColumn).hasMoreValues();
}
break;
case SKIP:
this.heap.next();
break;
case SEEK_NEXT_USING_HINT:
// TODO convert resee to Cell?
Cell nextKV = matcher.getNextKeyHint(cell);
if (nextKV != null) {
seekAsDirection(nextKV);
NextState stateAfterSeekByHint = needToReturn(outResult);
if (stateAfterSeekByHint != null) {
return scannerContext.setScannerState(stateAfterSeekByHint).hasMoreValues();
}
} else {
heap.next();
}
break;
default:
throw new RuntimeException("UNEXPECTED");
}
} while((cell = this.heap.peek()) != null);
if (count > 0) {
return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
}
// No more keys
close();
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
/**
* If the top cell won't be flushed into disk, the new top cell may be
* changed after #reopenAfterFlush. Because the older top cell only exist
* in the memstore scanner but the memstore scanner is replaced by hfile
* scanner after #reopenAfterFlush. If the row of top cell is changed,
* we should return the current cells. Otherwise, we may return
* the cells across different rows.
* @param outResult the cells which are visible for user scan
* @return null is the top cell doesn't change. Otherwise, the NextState
* to return
*/
private NextState needToReturn(List outResult) {
if (!outResult.isEmpty() && topChanged) {
return heap.peek() == null ? NextState.NO_MORE_VALUES : NextState.MORE_VALUES;
}
return null;
}
@Override
public long getReadPoint() {
return readPt;
}
private static void clearAndClose(List scanners) {
for (KeyValueScanner s : scanners) {
s.close();
}
scanners.clear();
}
// Implementation of ChangedReadersObserver
@Override
public void updateReaders(List sfs, List memStoreScanners) throws IOException {
if (CollectionUtils.isEmpty(sfs) && CollectionUtils.isEmpty(memStoreScanners)) {
return;
}
flushLock.lock();
try {
if (this.closing) {
// Lets close scanners created by caller, since close() won't notice this.
// memStoreScanners is immutable, so lets create a new list.
if (!CollectionUtils.isEmpty(memStoreScanners)) {
clearAndClose(new ArrayList<>(memStoreScanners));
}
return;
}
flushed = true;
final boolean isCompaction = false;
boolean usePread = get || scanUsePread;
// SEE HBASE-19468 where the flushed files are getting compacted even before a scanner
// calls next(). So its better we create scanners here rather than next() call. Ensure
// these scanners are properly closed() whether or not the scan is completed successfully
// Eagerly creating scanners so that we have the ref counting ticking on the newly created
// store files. In case of stream scanners this eager creation does not induce performance
// penalty because in scans (that uses stream scanners) the next() call is bound to happen.
List scanners = store.getScanners(sfs, cacheBlocks, get, usePread,
isCompaction, matcher, scan.getStartRow(), scan.getStopRow(), this.readPt, false);
flushedstoreFileScanners.addAll(scanners);
if (!CollectionUtils.isEmpty(memStoreScanners)) {
clearAndClose(memStoreScannersAfterFlush);
memStoreScannersAfterFlush.addAll(memStoreScanners);
}
} finally {
flushLock.unlock();
}
}
// Implementation of ChangedReadersObserver
protected void nullifyCurrentHeap() throws IOException {
if (this.closing) return;
// All public synchronized API calls will call 'checkReseek' which will cause
// the scanner stack to reseek if this.heap==null && this.lastTop != null.
// But if two calls to updateReaders() happen without a 'next' or 'peek' then we
// will end up calling this.peek() which would cause a reseek in the middle of a updateReaders
// which is NOT what we want, not to mention could cause an NPE. So we early out here.
if (this.heap == null) return;
// this could be null.
this.lastTop = this.heap.peek();
//DebugPrint.println("SS updateReaders, topKey = " + lastTop);
// close scanners to old obsolete Store files
this.heap.close(); // bubble thru and close all scanners.
this.heap = null; // the re-seeks could be slow (access HDFS) free up memory ASAP
// Let the next() call handle re-creating and seeking
}
private void seekOrSkipToNextRow(Cell cell) throws IOException {
// If it is a Get Scan, then we know that we are done with this row; there are no more
// rows beyond the current one: don't try to optimize.
if (!get) {
if (trySkipToNextRow(cell)) {
return;
}
}
seekToNextRow(cell);
}
private void seekOrSkipToNextColumn(Cell cell) throws IOException {
if (!trySkipToNextColumn(cell)) {
seekAsDirection(matcher.getKeyForNextColumn(cell));
}
}
/**
* See if we should actually SEEK or rather just SKIP to the next Cell (see HBASE-13109).
* ScanQueryMatcher may issue SEEK hints, such as seek to next column, next row, or seek to an
* arbitrary seek key. This method decides whether a seek is the most efficient _actual_ way to
* get us to the requested cell (SEEKs are more expensive than SKIP, SKIP, SKIP inside the
* current, loaded block). It does this by looking at the next indexed key of the current HFile.
* This key is then compared with the _SEEK_ key, where a SEEK key is an artificial 'last possible
* key on the row' (only in here, we avoid actually creating a SEEK key; in the compare we work
* with the current Cell but compare as though it were a seek key; see down in
* matcher.compareKeyForNextRow, etc). If the compare gets us onto the next block we *_SEEK,
* otherwise we just SKIP to the next requested cell.
*
* Other notes:
*
* - Rows can straddle block boundaries
* - Versions of columns can straddle block boundaries (i.e. column C1 at T1 might be in a
* different block than column C1 at T2)
* - We want to SKIP if the chance is high that we'll find the desired Cell after a few
* SKIPs...
* - We want to SEEK when the chance is high that we'll be able to seek past many Cells,
* especially if we know we need to go to the next block.
*
*
* A good proxy (best effort) to determine whether SKIP is better than SEEK is whether we'll
* likely end up seeking to the next block (or past the next block) to get our next column.
* Example:
*
*
* | BLOCK 1 | BLOCK 2 |
* | r1/c1, r1/c2, r1/c3 | r1/c4, r1/c5, r2/c1 |
* ^ ^
* | |
* Next Index Key SEEK_NEXT_ROW (before r2/c1)
*
*
* | BLOCK 1 | BLOCK 2 |
* | r1/c1/t5, r1/c1/t4, r1/c1/t3 | r1/c1/t2, r1/c1/T1, r1/c2/T3 |
* ^ ^
* | |
* Next Index Key SEEK_NEXT_COL
*
*
* Now imagine we want columns c1 and c3 (see first diagram above), the 'Next Index Key' of r1/c4
* is > r1/c3 so we should seek to get to the c1 on the next row, r2. In second case, say we only
* want one version of c1, after we have it, a SEEK_COL will be issued to get to c2. Looking at
* the 'Next Index Key', it would land us in the next block, so we should SEEK. In other scenarios
* where the SEEK will not land us in the next block, it is very likely better to issues a series
* of SKIPs.
* @param cell current cell
* @return true means skip to next row, false means not
*/
@VisibleForTesting
protected boolean trySkipToNextRow(Cell cell) throws IOException {
Cell nextCell = null;
// used to guard against a changed next indexed key by doing a identity comparison
// when the identity changes we need to compare the bytes again
Cell previousIndexedKey = null;
do {
Cell nextIndexedKey = getNextIndexedKey();
if (nextIndexedKey != null && nextIndexedKey != KeyValueScanner.NO_NEXT_INDEXED_KEY
&& (nextIndexedKey == previousIndexedKey
|| matcher.compareKeyForNextRow(nextIndexedKey, cell) >= 0)) {
this.heap.next();
++kvsScanned;
previousIndexedKey = nextIndexedKey;
} else {
return false;
}
nextCell = this.heap.peek();
} while (nextCell != null && CellUtil.matchingRow(cell, nextCell));
return true;
}
/**
* See {@link org.apache.hadoop.hbase.regionserver.StoreScanner#trySkipToNextRow(Cell)}
* @param cell current cell
* @return true means skip to next column, false means not
*/
@VisibleForTesting
protected boolean trySkipToNextColumn(Cell cell) throws IOException {
Cell nextCell = null;
// used to guard against a changed next indexed key by doing a identity comparison
// when the identity changes we need to compare the bytes again
Cell previousIndexedKey = null;
do {
Cell nextIndexedKey = getNextIndexedKey();
if (nextIndexedKey != null && nextIndexedKey != KeyValueScanner.NO_NEXT_INDEXED_KEY
&& (nextIndexedKey == previousIndexedKey
|| matcher.compareKeyForNextColumn(nextIndexedKey, cell) >= 0)) {
this.heap.next();
++kvsScanned;
previousIndexedKey = nextIndexedKey;
} else {
return false;
}
nextCell = this.heap.peek();
} while (nextCell != null && CellUtil.matchingRow(cell, nextCell)
&& CellUtil.matchingColumn(cell, nextCell));
// We need this check because it may happen that the new scanner that we get
// during heap.next() is requiring reseek due of fake KV previously generated for
// ROWCOL bloom filter optimization. See HBASE-19863 for more details
if (nextCell != null && matcher.compareKeyForNextColumn(nextCell, cell) < 0) {
return false;
}
return true;
}
/**
* @param flushed indicates if there was a flush
* @return true if top of heap has changed (and KeyValueHeap has to try the
* next KV)
* @throws IOException
*/
protected boolean checkReseek(boolean flushed) throws IOException {
if (flushed && this.lastTop != null) {
resetScannerStack(this.lastTop);
if (this.heap.peek() == null
|| store.getComparator().compareRows(this.lastTop, this.heap.peek()) != 0) {
LOG.info("Storescanner.peek() is changed where before = "
+ this.lastTop.toString() + ",and after = " + this.heap.peek());
this.lastTop = null;
topChanged = true;
return true;
}
this.lastTop = null; // gone!
}
// else dont need to reseek
topChanged = false;
return false;
}
protected void resetScannerStack(Cell lastTopKey) throws IOException {
/* When we have the scan object, should we not pass it to getScanners()
* to get a limited set of scanners? We did so in the constructor and we
* could have done it now by storing the scan object from the constructor
*/
final boolean isCompaction = false;
boolean usePread = get || scanUsePread;
List scanners = null;
flushLock.lock();
try {
List allScanners =
new ArrayList<>(flushedstoreFileScanners.size() + memStoreScannersAfterFlush.size());
allScanners.addAll(flushedstoreFileScanners);
allScanners.addAll(memStoreScannersAfterFlush);
scanners = selectScannersFrom(allScanners);
// Clear the current set of flushed store files so that they don't get added again
flushedstoreFileScanners.clear();
memStoreScannersAfterFlush.clear();
} finally {
flushLock.unlock();
}
// Seek the new scanners to the last key
seekScanners(scanners, lastTopKey, false, parallelSeekEnabled);
// remove the older memstore scanner
for (int i = 0; i < currentScanners.size(); i++) {
if (!currentScanners.get(i).isFileScanner()) {
scannersForDelayedClose.add(currentScanners.remove(i));
break;
}
}
// add the newly created scanners on the flushed files and the current active memstore scanner
addCurrentScanners(scanners);
// Combine all seeked scanners with a heap
resetKVHeap(this.currentScanners, store.getComparator());
// Reset the state of the Query Matcher and set to top row.
// Only reset and call setRow if the row changes; avoids confusing the
// query matcher if scanning intra-row.
Cell kv = heap.peek();
if (kv == null) {
kv = lastTopKey;
}
byte[] row = kv.getRowArray();
int offset = kv.getRowOffset();
short length = kv.getRowLength();
if ((matcher.row == null) || !Bytes.equals(row, offset, length, matcher.row,
matcher.rowOffset, matcher.rowLength)) {
this.countPerRow = 0;
matcher.reset();
matcher.setRow(row, offset, length);
}
}
/**
* Check whether scan as expected order
* @param prevKV
* @param kv
* @param comparator
* @throws IOException
*/
protected void checkScanOrder(Cell prevKV, Cell kv,
KeyValue.KVComparator comparator) throws IOException {
// Check that the heap gives us KVs in an increasing order.
assert prevKV == null || comparator == null
|| comparator.compare(prevKV, kv) <= 0 : "Key " + prevKV
+ " followed by a " + "smaller key " + kv + " in cf " + store;
}
protected boolean seekToNextRow(Cell kv) throws IOException {
return reseek(KeyValueUtil.createLastOnRow(kv));
}
/**
* Do a reseek in a normal StoreScanner(scan forward)
* @param kv
* @return true if scanner has values left, false if end of scanner
* @throws IOException
*/
protected boolean seekAsDirection(Cell kv)
throws IOException {
return reseek(kv);
}
@Override
public boolean reseek(Cell kv) throws IOException {
boolean flushed = checkFlushed();
// Heap will not be null, if this is called from next() which.
// If called from RegionScanner.reseek(...) make sure the scanner
// stack is reset if needed.
checkReseek(flushed);
if (explicitColumnQuery && lazySeekEnabledGlobally) {
return heap.requestSeek(kv, true, useRowColBloom);
}
return heap.reseek(kv);
}
protected boolean checkFlushed() {
// check the var without any lock. Suppose even if we see the old
// value here still it is ok to continue because we will not be resetting
// the heap but will continue with the referenced memstore's snapshot. For compactions
// any way we don't need the updateReaders at all to happen as we still continue with
// the older files
if (flushed) {
// If there is a flush and the current scan is notified on the flush ensure that the
// scan's heap gets reset and we do a seek on the newly flushed file.
if(!this.closing) {
this.lastTop = this.peek();
} else {
return false;
}
// reset the flag
flushed = false;
return true;
}
return false;
}
@Override
public long getSequenceID() {
return 0;
}
/**
* Seek storefiles in parallel to optimize IO latency as much as possible
* @param scanners the list {@link KeyValueScanner}s to be read from
* @param kv the KeyValue on which the operation is being requested
* @throws IOException
*/
private void parallelSeek(final List
scanners, final Cell kv) throws IOException {
if (scanners.isEmpty()) return;
int storeFileScannerCount = scanners.size();
CountDownLatch latch = new CountDownLatch(storeFileScannerCount);
List handlers =
new ArrayList(storeFileScannerCount);
for (KeyValueScanner scanner : scanners) {
if (scanner instanceof StoreFileScanner) {
ParallelSeekHandler seekHandler = new ParallelSeekHandler(scanner, kv,
this.readPt, latch);
executor.submit(seekHandler);
handlers.add(seekHandler);
} else {
scanner.seek(kv);
latch.countDown();
}
}
try {
latch.await();
} catch (InterruptedException ie) {
throw (InterruptedIOException)new InterruptedIOException().initCause(ie);
}
for (ParallelSeekHandler handler : handlers) {
if (handler.getErr() != null) {
throw new IOException(handler.getErr());
}
}
}
/**
* Used in testing.
* @return all scanners in no particular order
*/
List getAllScannersForTesting() {
List allScanners = new ArrayList();
KeyValueScanner current = heap.getCurrentForTesting();
if (current != null)
allScanners.add(current);
for (KeyValueScanner scanner : heap.getHeap())
allScanners.add(scanner);
return allScanners;
}
static void enableLazySeekGlobally(boolean enable) {
lazySeekEnabledGlobally = enable;
}
/**
* @return The estimated number of KVs seen by this scanner (includes some skipped KVs).
*/
public long getEstimatedNumberOfKvsScanned() {
return this.kvsScanned;
}
@Override
public Cell getNextIndexedKey() {
return this.heap.getNextIndexedKey();
}
}
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