org.apache.hadoop.hbase.regionserver.KeyValueHeap Maven / Gradle / Ivy
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* 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.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.regionserver.ScannerContext.NextState;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Implements a heap merge across any number of KeyValueScanners.
*
* Implements KeyValueScanner itself.
*
* This class is used at the Region level to merge across Stores and at the Store level to merge
* across the memstore and StoreFiles.
*
* In the Region case, we also need InternalScanner.next(List), so this class also implements
* InternalScanner. WARNING: As is, if you try to use this as an InternalScanner at the Store level,
* you will get runtime exceptions.
*/
@InterfaceAudience.Private
public class KeyValueHeap extends NonReversedNonLazyKeyValueScanner
implements KeyValueScanner, InternalScanner {
private static final Logger LOG = LoggerFactory.getLogger(KeyValueHeap.class);
protected PriorityQueue heap = null;
// Holds the scanners when a ever a eager close() happens. All such eagerly closed
// scans are collected and when the final scanner.close() happens will perform the
// actual close.
protected List scannersForDelayedClose = null;
/**
* The current sub-scanner, i.e. the one that contains the next key/value to return to the client.
* This scanner is NOT included in {@link #heap} (but we frequently add it back to the heap and
* pull the new winner out). We maintain an invariant that the current sub-scanner has already
* done a real seek, and that current.peek() is always a real key/value (or null) except for the
* fake last-key-on-row-column supplied by the multi-column Bloom filter optimization, which is OK
* to propagate to StoreScanner. In order to ensure that, always use {@link #pollRealKV()} to
* update current.
*/
protected KeyValueScanner current = null;
protected KVScannerComparator comparator;
/**
* Constructor. This KeyValueHeap will handle closing of passed in KeyValueScanners. nn
*/
public KeyValueHeap(List scanners, CellComparator comparator)
throws IOException {
this(scanners, new KVScannerComparator(comparator));
}
/**
* Constructor. nnn
*/
KeyValueHeap(List scanners, KVScannerComparator comparator)
throws IOException {
this.comparator = comparator;
this.scannersForDelayedClose = new ArrayList<>(scanners.size());
if (!scanners.isEmpty()) {
this.heap = new PriorityQueue<>(scanners.size(), this.comparator);
for (KeyValueScanner scanner : scanners) {
if (scanner.peek() != null) {
this.heap.add(scanner);
} else {
this.scannersForDelayedClose.add(scanner);
}
}
this.current = pollRealKV();
}
}
@Override
public Cell peek() {
if (this.current == null) {
return null;
}
return this.current.peek();
}
boolean isLatestCellFromMemstore() {
return !this.current.isFileScanner();
}
@Override
public Cell next() throws IOException {
if (this.current == null) {
return null;
}
Cell kvReturn = this.current.next();
Cell kvNext = this.current.peek();
if (kvNext == null) {
this.scannersForDelayedClose.add(this.current);
this.current = null;
this.current = pollRealKV();
} else {
KeyValueScanner topScanner = this.heap.peek();
// no need to add current back to the heap if it is the only scanner left
if (topScanner != null && this.comparator.compare(kvNext, topScanner.peek()) >= 0) {
this.heap.add(this.current);
this.current = null;
this.current = pollRealKV();
}
}
return kvReturn;
}
/**
* Gets the next row of keys from the top-most scanner.
*
* This method takes care of updating the heap.
*
* This can ONLY be called when you are using Scanners that implement InternalScanner as well as
* KeyValueScanner (a {@link StoreScanner}).
* @return true if more rows exist after this one, false if scanner is done
*/
@Override
public boolean next(List result, ScannerContext scannerContext) throws IOException {
if (this.current == null) {
return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
InternalScanner currentAsInternal = (InternalScanner) this.current;
boolean moreCells = currentAsInternal.next(result, scannerContext);
Cell pee = this.current.peek();
/*
* By definition, any InternalScanner must return false only when it has no further rows to be
* fetched. So, we can close a scanner if it returns false. All existing implementations seem to
* be fine with this. It is much more efficient to close scanners which are not needed than keep
* them in the heap. This is also required for certain optimizations.
*/
if (pee == null || !moreCells) {
// add the scanner that is to be closed
this.scannersForDelayedClose.add(this.current);
} else {
this.heap.add(this.current);
}
this.current = null;
this.current = pollRealKV();
if (this.current == null) {
moreCells = scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
}
return moreCells;
}
protected static class KVScannerComparator implements Comparator {
protected CellComparator kvComparator;
/**
* Constructor n
*/
public KVScannerComparator(CellComparator kvComparator) {
this.kvComparator = kvComparator;
}
@Override
public int compare(KeyValueScanner left, KeyValueScanner right) {
int comparison = compare(left.peek(), right.peek());
if (comparison != 0) {
return comparison;
} else {
// Since both the keys are exactly the same, we break the tie in favor of higher ordered
// scanner since it'll have newer data. Since higher value should come first, we reverse
// sort here.
return Long.compare(right.getScannerOrder(), left.getScannerOrder());
}
}
/**
* Compares two KeyValue nn * @return less than 0 if left is smaller, 0 if equal etc..
*/
public int compare(Cell left, Cell right) {
return this.kvComparator.compare(left, right);
}
/**
* n
*/
public CellComparator getComparator() {
return this.kvComparator;
}
}
@Override
public void close() {
for (KeyValueScanner scanner : this.scannersForDelayedClose) {
scanner.close();
}
this.scannersForDelayedClose.clear();
if (this.current != null) {
this.current.close();
}
if (this.heap != null) {
// Order of closing the scanners shouldn't matter here, so simply iterate and close them.
for (KeyValueScanner scanner : heap) {
scanner.close();
}
}
}
/**
* Seeks all scanners at or below the specified seek key. If we earlied-out of a row, we may end
* up skipping values that were never reached yet. Rather than iterating down, we want to give the
* opportunity to re-seek.
*
* As individual scanners may run past their ends, those scanners are automatically closed and
* removed from the heap.
*
* This function (and {@link #reseek(Cell)}) does not do multi-column Bloom filter and lazy-seek
* optimizations. To enable those, call {@link #requestSeek(Cell, boolean, boolean)}.
* @param seekKey KeyValue to seek at or after
* @return true if KeyValues exist at or after specified key, false if not n
*/
@Override
public boolean seek(Cell seekKey) throws IOException {
return generalizedSeek(false, // This is not a lazy seek
seekKey, false, // forward (false: this is not a reseek)
false); // Not using Bloom filters
}
/**
* This function is identical to the {@link #seek(Cell)} function except that
* scanner.seek(seekKey) is changed to scanner.reseek(seekKey).
*/
@Override
public boolean reseek(Cell seekKey) throws IOException {
return generalizedSeek(false, // This is not a lazy seek
seekKey, true, // forward (true because this is reseek)
false); // Not using Bloom filters
}
/**
* {@inheritDoc}
*/
@Override
public boolean requestSeek(Cell key, boolean forward, boolean useBloom) throws IOException {
return generalizedSeek(true, key, forward, useBloom);
}
/**
* @param isLazy whether we are trying to seek to exactly the given row/col. Enables Bloom
* filter and most-recent-file-first optimizations for multi-column get/scan
* queries.
* @param seekKey key to seek to
* @param forward whether to seek forward (also known as reseek)
* @param useBloom whether to optimize seeks using Bloom filters
*/
private boolean generalizedSeek(boolean isLazy, Cell seekKey, boolean forward, boolean useBloom)
throws IOException {
if (!isLazy && useBloom) {
throw new IllegalArgumentException(
"Multi-column Bloom filter " + "optimization requires a lazy seek");
}
if (current == null) {
return false;
}
KeyValueScanner scanner = current;
try {
while (scanner != null) {
Cell topKey = scanner.peek();
if (comparator.getComparator().compare(seekKey, topKey) <= 0) {
// Top KeyValue is at-or-after Seek KeyValue. We only know that all
// scanners are at or after seekKey (because fake keys of
// scanners where a lazy-seek operation has been done are not greater
// than their real next keys) but we still need to enforce our
// invariant that the top scanner has done a real seek. This way
// StoreScanner and RegionScanner do not have to worry about fake
// keys.
heap.add(scanner);
scanner = null;
current = pollRealKV();
return current != null;
}
boolean seekResult;
if (isLazy && heap.size() > 0) {
// If there is only one scanner left, we don't do lazy seek.
seekResult = scanner.requestSeek(seekKey, forward, useBloom);
} else {
seekResult = NonLazyKeyValueScanner.doRealSeek(scanner, seekKey, forward);
}
if (!seekResult) {
this.scannersForDelayedClose.add(scanner);
} else {
heap.add(scanner);
}
scanner = heap.poll();
if (scanner == null) {
current = null;
}
}
} catch (Exception e) {
if (scanner != null) {
try {
scanner.close();
} catch (Exception ce) {
LOG.warn("close KeyValueScanner error", ce);
}
}
throw e;
}
// Heap is returning empty, scanner is done
return false;
}
/**
* Fetches the top sub-scanner from the priority queue, ensuring that a real seek has been done on
* it. Works by fetching the top sub-scanner, and if it has not done a real seek, making it do so
* (which will modify its top KV), putting it back, and repeating this until success. Relies on
* the fact that on a lazy seek we set the current key of a StoreFileScanner to a KV that is not
* greater than the real next KV to be read from that file, so the scanner that bubbles up to the
* top of the heap will have global next KV in this scanner heap if (1) it has done a real seek
* and (2) its KV is the top among all top KVs (some of which are fake) in the scanner heap.
*/
protected KeyValueScanner pollRealKV() throws IOException {
KeyValueScanner kvScanner = heap.poll();
if (kvScanner == null) {
return null;
}
while (kvScanner != null && !kvScanner.realSeekDone()) {
if (kvScanner.peek() != null) {
try {
kvScanner.enforceSeek();
} catch (IOException ioe) {
// Add the item to delayed close set in case it is leak from close
this.scannersForDelayedClose.add(kvScanner);
throw ioe;
}
Cell curKV = kvScanner.peek();
if (curKV != null) {
KeyValueScanner nextEarliestScanner = heap.peek();
if (nextEarliestScanner == null) {
// The heap is empty. Return the only possible scanner.
return kvScanner;
}
// Compare the current scanner to the next scanner. We try to avoid
// putting the current one back into the heap if possible.
Cell nextKV = nextEarliestScanner.peek();
if (nextKV == null || comparator.compare(curKV, nextKV) < 0) {
// We already have the scanner with the earliest KV, so return it.
return kvScanner;
}
// Otherwise, put the scanner back into the heap and let it compete
// against all other scanners (both those that have done a "real
// seek" and a "lazy seek").
heap.add(kvScanner);
} else {
// Close the scanner because we did a real seek and found out there
// are no more KVs.
this.scannersForDelayedClose.add(kvScanner);
}
} else {
// Close the scanner because it has already run out of KVs even before
// we had to do a real seek on it.
this.scannersForDelayedClose.add(kvScanner);
}
kvScanner = heap.poll();
}
return kvScanner;
}
/**
* @return the current Heap
*/
public PriorityQueue getHeap() {
return this.heap;
}
KeyValueScanner getCurrentForTesting() {
return current;
}
@Override
public Cell getNextIndexedKey() {
// here we return the next index key from the top scanner
return current == null ? null : current.getNextIndexedKey();
}
@Override
public void shipped() throws IOException {
for (KeyValueScanner scanner : this.scannersForDelayedClose) {
scanner.close(); // There wont be further fetch of Cells from these scanners. Just close.
}
this.scannersForDelayedClose.clear();
if (this.current != null) {
this.current.shipped();
}
if (this.heap != null) {
for (KeyValueScanner scanner : this.heap) {
scanner.shipped();
}
}
}
}
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