/**
*
* 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 com.google.common.annotations.VisibleForTesting;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
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.CellComparator;
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.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.regionserver.querymatcher.CompactionScanQueryMatcher;
import org.apache.hadoop.hbase.regionserver.querymatcher.LegacyScanQueryMatcher;
import org.apache.hadoop.hbase.regionserver.querymatcher.ScanQueryMatcher;
import org.apache.hadoop.hbase.regionserver.querymatcher.UserScanQueryMatcher;
import org.apache.hadoop.hbase.util.CollectionUtils;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
/**
* Scanner scans both the memstore and the Store. Coalesce KeyValue stream into List<KeyValue>
* for a single row.
* <p>
* The implementation is not thread safe. So there will be no race between next and close. The only
* exception is updateReaders, it will be called in the memstore flush thread to indicate that there
* is a flush.
*/
@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;
private ScanQueryMatcher matcher;
protected KeyValueHeap heap;
private boolean cacheBlocks;
private long countPerRow = 0;
private int storeLimit = -1;
private int storeOffset = 0;
// Used to indicate that the scanner has closed (see HBASE-1107)
// Do not need to be volatile because it's always accessed via synchronized methods
private boolean closing = false;
private final boolean get;
private final boolean explicitColumnQuery;
private final boolean useRowColBloom;
/**
* A flag that enables StoreFileScanner parallel-seeking
*/
private boolean parallelSeekEnabled = false;
private ExecutorService executor;
private final Scan scan;
private final long oldestUnexpiredTS;
private final long now;
private final int minVersions;
private final long maxRowSize;
private final long cellsPerHeartbeatCheck;
// Collects all the KVHeap that are eagerly getting closed during the
// course of a scan
private final List<KeyValueHeap> heapsForDelayedClose = 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;
private final long preadMaxBytes;
private long bytesRead;
/** 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 */
private 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 the read type if Scan.ReadType.DEFAULT, we will start with pread, and if the kvs we scanned
* reaches this limit, we will reopen the scanner with stream. The default value is 4 times of
* block size for this store.
*/
public static final String STORESCANNER_PREAD_MAX_BYTES = "hbase.storescanner.pread.max.bytes";
private final Scan.ReadType readType;
// A flag whether use pread for scan
// it maybe changed if we use Scan.ReadType.DEFAULT and we have read lots of data.
private boolean scanUsePread;
// 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<StoreFile> flushedStoreFiles = new ArrayList<>(1);
// Since CompactingMemstore is now default, we get three memstore scanners from a flush
private final List<KeyValueScanner> memStoreScannersAfterFlush = new ArrayList<>(3);
// The current list of scanners
@VisibleForTesting
final List<KeyValueScanner> currentScanners = new ArrayList<>();
// flush update lock
private final ReentrantLock flushLock = new ReentrantLock();
protected final long readPt;
// 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<byte[]> 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.now = EnvironmentEdgeManager.currentTime();
this.oldestUnexpiredTS = scan.isRaw() ? 0L : 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<byte[]>).
this.useRowColBloom = numCol > 1 || (!get && numCol == 1);
this.maxRowSize = scanInfo.getTableMaxRowSize();
if (get) {
this.readType = Scan.ReadType.PREAD;
this.scanUsePread = true;
} else {
if (scan.getReadType() == Scan.ReadType.DEFAULT) {
this.readType = scanInfo.isUsePread() ? Scan.ReadType.PREAD : Scan.ReadType.DEFAULT;
} else {
this.readType = scan.getReadType();
}
// Always start with pread unless user specific stream. Will change to stream later if
// readType is default if the scan keeps running for a long time.
this.scanUsePread = this.readType != Scan.ReadType.STREAM;
}
this.preadMaxBytes = scanInfo.getPreadMaxBytes();
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();
}
}
}
private void addCurrentScanners(List<? extends KeyValueScanner> 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<byte[]> 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 = UserScanQueryMatcher.create(scan, scanInfo, columns, oldestUnexpiredTS, now,
store.getCoprocessorHost());
this.store.addChangedReaderObserver(this);
try {
// Pass columns to try to filter out unnecessary StoreFiles.
List<KeyValueScanner> 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.<p>
*
* 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<? extends KeyValueScanner> 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.<p>
*
* 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<? extends KeyValueScanner> 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<? extends KeyValueScanner> 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 (scan.hasFilter() || (scan.getStartRow() != null && scan.getStartRow().length > 0)
|| (scan.getStopRow() != null && scan.getStopRow().length > 0)
|| !scan.getTimeRange().isAllTime()) {
// use legacy query matcher since we do not consider the scan object in our code. Only used to
// keep compatibility for coprocessor.
matcher = LegacyScanQueryMatcher.create(scan, scanInfo, null, scanType, smallestReadPoint,
earliestPutTs, oldestUnexpiredTS, now, dropDeletesFromRow, dropDeletesToRow,
store.getCoprocessorHost());
} else {
matcher = CompactionScanQueryMatcher.create(scanInfo, scanType, 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<byte[]> columns,
final List<? extends KeyValueScanner> 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<byte[]> columns,
final List<? extends KeyValueScanner> scanners, long earliestPutTs)
throws IOException {
this(scan, scanInfo, scanType, columns, scanners, earliestPutTs,
// 0 is passed as readpoint because the test bypasses Store
0);
}
public StoreScanner(final Scan scan, ScanInfo scanInfo, ScanType scanType,
final NavigableSet<byte[]> columns, final List<? extends KeyValueScanner> scanners, long earliestPutTs,
long readPt) throws IOException {
this(null, scan, scanInfo, columns, readPt,
scanType == ScanType.USER_SCAN ? scan.getCacheBlocks() : false);
if (scanType == ScanType.USER_SCAN) {
this.matcher = UserScanQueryMatcher.create(scan, scanInfo, columns, oldestUnexpiredTS, now,
null);
} else {
if (scan.hasFilter() || (scan.getStartRow() != null && scan.getStartRow().length > 0)
|| (scan.getStopRow() != null && scan.getStopRow().length > 0)
|| !scan.getTimeRange().isAllTime() || columns != null) {
// use legacy query matcher since we do not consider the scan object in our code. Only used
// to keep compatibility for coprocessor.
matcher = LegacyScanQueryMatcher.create(scan, scanInfo, columns, scanType, Long.MAX_VALUE,
earliestPutTs, oldestUnexpiredTS, now, null, null, store.getCoprocessorHost());
} else {
this.matcher = CompactionScanQueryMatcher.create(scanInfo, scanType, Long.MAX_VALUE,
earliestPutTs, oldestUnexpiredTS, now, null, null, null);
}
}
// 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
*/
private List<KeyValueScanner> getScannersNoCompaction() throws IOException {
return selectScannersFrom(
store.getScanners(cacheBlocks, scanUsePread, false, matcher, scan.getStartRow(),
scan.includeStartRow(), scan.getStopRow(), scan.includeStopRow(), 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<? extends KeyValueScanner> 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 (matcher.isUserScan() && 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<? extends KeyValueScanner> scanners,
CellComparator 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.
* <p>
* Will be overridden by testcase so declared as protected.
*/
@VisibleForTesting
protected List<KeyValueScanner> selectScannersFrom(
final List<? extends KeyValueScanner> 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<KeyValueScanner> 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() {
return heap != null ? heap.peek() : null;
}
@Override
public KeyValue next() {
// throw runtime exception perhaps?
throw new RuntimeException("Never call StoreScanner.next()");
}
@Override
public void close() {
close(true);
}
private void close(boolean withHeapClose) {
if (this.closing) {
return;
}
if (withHeapClose) {
this.closing = true;
}
// Under test, we dont have a this.store
if (this.store != null) {
this.store.deleteChangedReaderObserver(this);
}
if (withHeapClose) {
clearAndClose(memStoreScannersAfterFlush);
for (KeyValueHeap h : this.heapsForDelayedClose) {
h.close();
}
this.heapsForDelayedClose.clear();
if (this.heap != null) {
this.heap.close();
this.currentScanners.clear();
this.heap = null; // CLOSED!
}
} else {
if (this.heap != null) {
this.heapsForDelayedClose.add(this.heap);
this.currentScanners.clear();
this.heap = null;
}
}
}
@Override
public boolean seek(Cell key) throws IOException {
if (checkFlushed()) {
reopenAfterFlush();
}
return this.heap.seek(key);
}
@Override
public boolean next(List<Cell> 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<Cell> outResult, ScannerContext scannerContext) throws IOException {
if (scannerContext == null) {
throw new IllegalArgumentException("Scanner context cannot be null");
}
if (checkFlushed() && reopenAfterFlush()) {
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) {
// By this time partial close should happened because already heap is null
close(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
Cell cell = this.heap.peek();
if (cell == null) {
close(false);// Do all cleanup except heap.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
// 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.currentRow() == null) {
this.countPerRow = 0;
matcher.setToNewRow(cell);
}
// 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.
CellComparator 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();
}
}
// Do object compare - we set prevKV from the same heap.
if (prevCell != cell) {
++kvsScanned;
}
checkScanOrder(prevCell, cell, comparator);
int cellSize = CellUtil.estimatedSerializedSizeOf(cell);
bytesRead += cellSize;
prevCell = cell;
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) {
cell = f.transformCell(cell);
}
this.countPerRow++;
if (storeLimit > -1 && this.countPerRow > (storeLimit + storeOffset)) {
// do what SEEK_NEXT_ROW does.
if (!matcher.moreRowsMayExistAfter(cell)) {
close(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
matcher.clearCurrentRow();
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 += cellSize;
// Update the progress of the scanner context
scannerContext.incrementSizeProgress(cellSize, CellUtil.estimatedHeapSizeOf(cell));
scannerContext.incrementBatchProgress(1);
if (matcher.isUserScan() && 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)) {
close(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
matcher.clearCurrentRow();
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 (get) {
// Then no more to this row... exit.
close(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
matcher.clearCurrentRow();
return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
case DONE_SCAN:
close(false);// Do all cleanup except heap.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)) {
close(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
matcher.clearCurrentRow();
seekOrSkipToNextRow(cell);
break;
case SEEK_NEXT_COL:
seekOrSkipToNextColumn(cell);
break;
case SKIP:
this.heap.next();
break;
case SEEK_NEXT_USING_HINT:
Cell nextKV = matcher.getNextKeyHint(cell);
if (nextKV != null) {
seekAsDirection(nextKV);
} 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(false);// Do all cleanup except heap.close()
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
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.
*
* <p>Other notes:
* <ul>
* <li>Rows can straddle block boundaries</li>
* <li>Versions of columns can straddle block boundaries (i.e. column C1 at T1 might be in a
* different block than column C1 at T2)</li>
* <li>We want to SKIP if the chance is high that we'll find the desired Cell after a
* few SKIPs...</li>
* <li>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.</li>
* </ul>
* <p>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:
* <pre>
* | 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
* </pre>
* 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;
do {
Cell nextIndexedKey = getNextIndexedKey();
if (nextIndexedKey != null && nextIndexedKey != KeyValueScanner.NO_NEXT_INDEXED_KEY
&& matcher.compareKeyForNextRow(nextIndexedKey, cell) >= 0) {
this.heap.next();
++kvsScanned;
} else {
return false;
}
} while ((nextCell = this.heap.peek()) != null && CellUtil.matchingRows(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;
do {
Cell nextIndexedKey = getNextIndexedKey();
if (nextIndexedKey != null && nextIndexedKey != KeyValueScanner.NO_NEXT_INDEXED_KEY
&& matcher.compareKeyForNextColumn(nextIndexedKey, cell) >= 0) {
this.heap.next();
++kvsScanned;
} else {
return false;
}
} while ((nextCell = this.heap.peek()) != null && CellUtil.matchingRowColumn(cell, nextCell));
return true;
}
@Override
public long getReadPoint() {
return this.readPt;
}
private static void clearAndClose(List<KeyValueScanner> scanners) {
for (KeyValueScanner s : scanners) {
s.close();
}
scanners.clear();
}
// Implementation of ChangedReadersObserver
@Override
public void updateReaders(List<StoreFile> sfs, List<KeyValueScanner> memStoreScanners) throws IOException {
if (CollectionUtils.isEmpty(sfs)
&& CollectionUtils.isEmpty(memStoreScanners)) {
return;
}
flushLock.lock();
try {
flushed = true;
flushedStoreFiles.addAll(sfs);
if (!CollectionUtils.isEmpty(memStoreScanners)) {
clearAndClose(memStoreScannersAfterFlush);
memStoreScannersAfterFlush.addAll(memStoreScanners);
}
} finally {
flushLock.unlock();
}
// Let the next() call handle re-creating and seeking
}
/**
* @return if top of heap has changed (and KeyValueHeap has to try the next KV)
*/
protected final boolean reopenAfterFlush() throws IOException {
Cell lastTop = heap.peek();
// 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
List<KeyValueScanner> scanners;
flushLock.lock();
try {
List<KeyValueScanner> allScanners = new ArrayList<>(flushedStoreFiles.size() + memStoreScannersAfterFlush.size());
allScanners.addAll(store.getScanners(flushedStoreFiles, cacheBlocks, get,
scanUsePread, false, matcher, scan.getStartRow(), scan.getStopRow(), this.readPt, false));
allScanners.addAll(memStoreScannersAfterFlush);
scanners = selectScannersFrom(allScanners);
// Clear the current set of flushed store files so that they don't get added again
flushedStoreFiles.clear();
memStoreScannersAfterFlush.clear();
} finally {
flushLock.unlock();
}
// Seek the new scanners to the last key
seekScanners(scanners, lastTop, false, parallelSeekEnabled);
// remove the older memstore scanner
for (int i = currentScanners.size() - 1; i >=0; i--) {
if (!currentScanners.get(i).isFileScanner()) {
currentScanners.remove(i).close();
} else {
// we add the memstore scanner to the end of currentScanners
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());
resetQueryMatcher(lastTop);
if (heap.peek() == null || store.getComparator().compareRows(lastTop, this.heap.peek()) != 0) {
if (LOG.isDebugEnabled()) {
LOG.debug("Storescanner.peek() is changed where before = " + lastTop.toString() +
",and after = " + heap.peek());
}
return true;
}
return false;
}
private void resetQueryMatcher(Cell lastTopKey) {
// 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 cell = heap.peek();
if (cell == null) {
cell = lastTopKey;
}
if ((matcher.currentRow() == null) || !CellUtil.matchingRows(cell, matcher.currentRow())) {
this.countPerRow = 0;
// The setToNewRow will call reset internally
matcher.setToNewRow(cell);
}
}
/**
* Check whether scan as expected order
* @param prevKV
* @param kv
* @param comparator
* @throws IOException
*/
protected void checkScanOrder(Cell prevKV, Cell kv,
CellComparator 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 c) throws IOException {
return reseek(CellUtil.createLastOnRow(c));
}
/**
* 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 {
if (checkFlushed()) {
reopenAfterFlush();
}
if (explicitColumnQuery && lazySeekEnabledGlobally) {
return heap.requestSeek(kv, true, useRowColBloom);
}
return heap.reseek(kv);
}
private void trySwitchToStreamRead() {
if (readType != Scan.ReadType.DEFAULT || !scanUsePread || closing || heap.peek() == null ||
bytesRead < preadMaxBytes) {
return;
}
if (LOG.isDebugEnabled()) {
LOG.debug("Switch to stream read because we have already read " + bytesRead +
" bytes from this scanner");
}
scanUsePread = false;
Cell lastTop = heap.peek();
Map<String, StoreFile> name2File = new HashMap<>(store.getStorefilesCount());
for (StoreFile file : store.getStorefiles()) {
name2File.put(file.getFileInfo().getActiveFileName(), file);
}
List<StoreFile> filesToReopen = new ArrayList<>();
List<KeyValueScanner> memstoreScanners = new ArrayList<>();
List<KeyValueScanner> scannersToClose = new ArrayList<>();
for (KeyValueScanner kvs : currentScanners) {
if (!kvs.isFileScanner()) {
memstoreScanners.add(kvs);
} else {
scannersToClose.add(kvs);
if (kvs.peek() == null) {
continue;
}
filesToReopen.add(name2File.get(kvs.getFilePath().getName()));
}
}
if (filesToReopen.isEmpty()) {
return;
}
List<KeyValueScanner> fileScanners = null;
List<KeyValueScanner> newCurrentScanners;
KeyValueHeap newHeap;
try {
fileScanners =
store.getScanners(filesToReopen, cacheBlocks, false, false, matcher, scan.getStartRow(),
scan.includeStartRow(), scan.getStopRow(), scan.includeStopRow(), readPt, false);
seekScanners(fileScanners, lastTop, false, parallelSeekEnabled);
newCurrentScanners = new ArrayList<>(fileScanners.size() + memstoreScanners.size());
newCurrentScanners.addAll(fileScanners);
newCurrentScanners.addAll(memstoreScanners);
newHeap = new KeyValueHeap(newCurrentScanners, store.getComparator());
} catch (Exception e) {
LOG.warn("failed to switch to stream read", e);
if (fileScanners != null) {
fileScanners.forEach(KeyValueScanner::close);
}
return;
}
currentScanners.clear();
addCurrentScanners(newCurrentScanners);
this.heap = newHeap;
resetQueryMatcher(lastTop);
scannersToClose.forEach(KeyValueScanner::close);
}
protected final 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) {
return false;
}
// reset the flag
flushed = false;
return true;
}
return false;
}
/**
* @see KeyValueScanner#getScannerOrder()
*/
@Override
public long getScannerOrder() {
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<? extends KeyValueScanner>
scanners, final Cell kv) throws IOException {
if (scanners.isEmpty()) return;
int storeFileScannerCount = scanners.size();
CountDownLatch latch = new CountDownLatch(storeFileScannerCount);
List<ParallelSeekHandler> 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
*/
@VisibleForTesting
List<KeyValueScanner> getAllScannersForTesting() {
List<KeyValueScanner> 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();
}
@Override
public void shipped() throws IOException {
if (prevCell != null) {
// Do the copy here so that in case the prevCell ref is pointing to the previous
// blocks we can safely release those blocks.
// This applies to blocks that are got from Bucket cache, L1 cache and the blocks
// fetched from HDFS. Copying this would ensure that we let go the references to these
// blocks so that they can be GCed safely(in case of bucket cache)
prevCell = KeyValueUtil.toNewKeyCell(this.prevCell);
}
matcher.beforeShipped();
// There wont be further fetch of Cells from these scanners. Just close.
this.heapsForDelayedClose.forEach(KeyValueHeap::close);
this.heapsForDelayedClose.clear();
if (this.heap != null) {
this.heap.shipped();
// When switching from pread to stream, we will open a new scanner for each store file, but
// the old scanner may still track the HFileBlocks we have scanned but not sent back to client
// yet. If we close the scanner immediately then the HFileBlocks may be messed up by others
// before we serialize and send it back to client. The HFileBlocks will be released in shipped
// method, so we here will also open new scanners and close old scanners in shipped method.
// See HBASE-18055 for more details.
trySwitchToStreamRead();
}
}
}