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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* 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.cassandra.io.sstable;
import java.util.*;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Functions;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.DataTracker;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.RowIndexEntry;
import org.apache.cassandra.db.compaction.AbstractCompactedRow;
import org.apache.cassandra.utils.CLibrary;
import org.apache.cassandra.utils.FBUtilities;
/**
* Wraps one or more writers as output for rewriting one or more readers: every sstable_preemptive_open_interval_in_mb
* we look in the summary we're collecting for the latest writer for the penultimate key that we know to have been fully
* flushed to the index file, and then double check that the key is fully present in the flushed data file.
* Then we move the starts of each reader forwards to that point, replace them in the datatracker, and attach a runnable
* for on-close (i.e. when all references expire) that drops the page cache prior to that key position
*
* hard-links are created for each partially written sstable so that readers opened against them continue to work past
* the rename of the temporary file, which is deleted once all readers against the hard-link have been closed.
* If for any reason the writer is rolled over, we immediately rename and fully expose the completed file in the DataTracker.
*
* On abort we restore the original lower bounds to the existing readers and delete any temporary files we had in progress,
* but leave any hard-links in place for the readers we opened to cleanup when they're finished as we would had we finished
* successfully.
*/
public class SSTableRewriter
{
private static long preemptiveOpenInterval;
static
{
long interval = DatabaseDescriptor.getSSTablePreempiveOpenIntervalInMB() * (1L << 20);
if (interval < 0)
interval = Long.MAX_VALUE;
preemptiveOpenInterval = interval;
}
@VisibleForTesting
static void overrideOpenInterval(long size)
{
preemptiveOpenInterval = size;
}
private final DataTracker dataTracker;
private final ColumnFamilyStore cfs;
private final long maxAge;
private final List finished = new ArrayList<>();
private final Set rewriting; // the readers we are rewriting (updated as they are replaced)
private final Map originalStarts = new HashMap<>(); // the start key for each reader we are rewriting
private final Map fileDescriptors = new HashMap<>(); // the file descriptors for each reader descriptor we are rewriting
private SSTableReader currentlyOpenedEarly; // the reader for the most recent (re)opening of the target file
private long currentlyOpenedEarlyAt; // the position (in MB) in the target file we last (re)opened at
private final Queue finishedEarly = new ArrayDeque<>();
// as writers are closed from finishedEarly, their last readers are moved
// into discard, so that abort can cleanup after us safely
private final List discard = new ArrayList<>();
private final boolean isOffline; // true for operations that are performed without Cassandra running (prevents updates of DataTracker)
private SSTableWriter writer;
private Map cachedKeys = new HashMap<>();
public SSTableRewriter(ColumnFamilyStore cfs, Set rewriting, long maxAge, boolean isOffline)
{
this.rewriting = rewriting;
for (SSTableReader sstable : rewriting)
{
originalStarts.put(sstable.descriptor, sstable.first);
fileDescriptors.put(sstable.descriptor, CLibrary.getfd(sstable.getFilename()));
}
this.dataTracker = cfs.getDataTracker();
this.cfs = cfs;
this.maxAge = maxAge;
this.isOffline = isOffline;
}
public SSTableWriter currentWriter()
{
return writer;
}
public RowIndexEntry append(AbstractCompactedRow row)
{
// we do this before appending to ensure we can resetAndTruncate() safely if the append fails
maybeReopenEarly(row.key);
RowIndexEntry index = writer.append(row);
if (!isOffline)
{
if (index == null)
{
cfs.invalidateCachedRow(row.key);
}
else
{
boolean save = false;
for (SSTableReader reader : rewriting)
{
if (reader.getCachedPosition(row.key, false) != null)
{
save = true;
break;
}
}
if (save)
cachedKeys.put(row.key, index);
}
}
return index;
}
// attempts to append the row, if fails resets the writer position
public RowIndexEntry tryAppend(AbstractCompactedRow row)
{
writer.mark();
try
{
return append(row);
}
catch (Throwable t)
{
writer.resetAndTruncate();
throw t;
}
}
private void maybeReopenEarly(DecoratedKey key)
{
if (!FBUtilities.isWindows() && writer.getFilePointer() - currentlyOpenedEarlyAt > preemptiveOpenInterval)
{
if (isOffline)
{
for (SSTableReader reader : rewriting)
{
RowIndexEntry index = reader.getPosition(key, SSTableReader.Operator.GE);
CLibrary.trySkipCache(fileDescriptors.get(reader.descriptor), 0, index == null ? 0 : index.position);
}
}
else
{
SSTableReader reader = writer.openEarly(maxAge);
if (reader != null)
{
replaceEarlyOpenedFile(currentlyOpenedEarly, reader);
currentlyOpenedEarly = reader;
currentlyOpenedEarlyAt = writer.getFilePointer();
moveStarts(reader, Functions.constant(reader.last), false);
}
}
}
}
public void abort()
{
switchWriter(null, true);
moveStarts(null, Functions.forMap(originalStarts), true);
// remove already completed SSTables
for (SSTableReader sstable : finished)
{
sstable.markObsolete();
sstable.sharedRef().release();
}
// abort the writers
for (Finished finished : finishedEarly)
{
boolean opened = finished.reader != null;
finished.writer.abort(!opened);
if (opened)
{
// if we've already been opened, add ourselves to the discard pile
discard.add(finished.reader);
finished.reader.markObsolete();
}
}
replaceWithFinishedReaders(Collections.emptyList());
}
/**
* Replace the readers we are rewriting with cloneWithNewStart, reclaiming any page cache that is no longer
* needed, and transferring any key cache entries over to the new reader, expiring them from the old. if reset
* is true, we are instead restoring the starts of the readers from before the rewriting began
*
* note that we replace an existing sstable with a new *instance* of the same sstable, the replacement
* sstable .equals() the old one, BUT, it is a new instance, so, for example, since we releaseReference() on the old
* one, the old *instance* will have reference count == 0 and if we were to start a new compaction with that old
* instance, we would get exceptions.
*
* @param newReader the rewritten reader that replaces them for this region
* @param newStarts a function mapping a reader's descriptor to their new start value
* @param reset true iff we are restoring earlier starts (increasing the range over which they are valid)
*/
private void moveStarts(SSTableReader newReader, Function newStarts, boolean reset)
{
if (isOffline)
return;
List toReplace = new ArrayList<>();
List replaceWith = new ArrayList<>();
final List invalidateKeys = new ArrayList<>();
if (!reset)
{
invalidateKeys.addAll(cachedKeys.keySet());
for (Map.Entry cacheKey : cachedKeys.entrySet())
newReader.cacheKey(cacheKey.getKey(), cacheKey.getValue());
}
cachedKeys = new HashMap<>();
for (final SSTableReader sstable : rewriting)
{
DecoratedKey newStart = newStarts.apply(sstable.descriptor);
assert newStart != null;
if (sstable.first.compareTo(newStart) < 0 || (reset && newStart != sstable.first))
{
toReplace.add(sstable);
// we call getCurrentReplacement() to support multiple rewriters operating over the same source readers at once.
// note: only one such writer should be written to at any moment
replaceWith.add(sstable.getCurrentReplacement().cloneWithNewStart(newStart, new Runnable()
{
public void run()
{
// this is somewhat racey, in that we could theoretically be closing this old reader
// when an even older reader is still in use, but it's not likely to have any major impact
for (DecoratedKey key : invalidateKeys)
sstable.invalidateCacheKey(key);
}
}));
}
}
cfs.getDataTracker().replaceWithNewInstances(toReplace, replaceWith);
rewriting.removeAll(toReplace);
rewriting.addAll(replaceWith);
}
private void replaceEarlyOpenedFile(SSTableReader toReplace, SSTableReader replaceWith)
{
if (isOffline)
return;
Set toReplaceSet;
if (toReplace != null)
{
toReplace.setReplacedBy(replaceWith);
toReplaceSet = Collections.singleton(toReplace);
}
else
{
dataTracker.markCompacting(Collections.singleton(replaceWith));
toReplaceSet = Collections.emptySet();
}
dataTracker.replaceEarlyOpenedFiles(toReplaceSet, Collections.singleton(replaceWith));
}
public void switchWriter(SSTableWriter newWriter)
{
switchWriter(newWriter, false);
}
private void switchWriter(SSTableWriter newWriter, boolean abort)
{
if (writer == null)
{
writer = newWriter;
return;
}
// we leave it as a tmp file, but we open it and add it to the dataTracker
if (writer.getFilePointer() != 0 && !abort)
{
SSTableReader reader = writer.finish(SSTableWriter.FinishType.EARLY, maxAge, -1);
replaceEarlyOpenedFile(currentlyOpenedEarly, reader);
moveStarts(reader, Functions.constant(reader.last), false);
finishedEarly.add(new Finished(writer, reader));
}
else
{
writer.abort();
}
currentlyOpenedEarly = null;
currentlyOpenedEarlyAt = 0;
writer = newWriter;
}
public List finish()
{
return finish(-1);
}
/**
* Finishes the new file(s)
*
* Creates final files, adds the new files to the dataTracker (via replaceReader).
*
* We add them to the tracker to be able to get rid of the tmpfiles
*
* It is up to the caller to do the compacted sstables replacement
* gymnastics (ie, call DataTracker#markCompactedSSTablesReplaced(..))
*
*
* @param repairedAt the repair time, -1 if we should use the time we supplied when we created
* the SSTableWriter (and called rewriter.switchWriter(..)), actual time if we want to override the
* repair time.
*/
public List finish(long repairedAt)
{
return finishAndMaybeThrow(repairedAt, false, false);
}
@VisibleForTesting
void finishAndThrow(boolean throwEarly)
{
finishAndMaybeThrow(-1, throwEarly, !throwEarly);
}
private List finishAndMaybeThrow(long repairedAt, boolean throwEarly, boolean throwLate)
{
List newReaders = new ArrayList<>();
switchWriter(null, false);
if (throwEarly)
throw new RuntimeException("exception thrown early in finish, for testing");
while (!finishedEarly.isEmpty())
{
Finished f = finishedEarly.poll();
if (f.writer.getFilePointer() > 0)
{
if (f.reader != null)
discard.add(f.reader);
SSTableReader newReader = f.writer.finish(SSTableWriter.FinishType.FINISH_EARLY, maxAge, repairedAt);
if (f.reader != null)
f.reader.setReplacedBy(newReader);
finished.add(newReader);
newReaders.add(newReader);
}
else
{
f.writer.abort(true);
assert f.reader == null;
}
}
if (throwLate)
throw new RuntimeException("exception thrown after all sstables finished, for testing");
replaceWithFinishedReaders(newReaders);
return finished;
}
// cleanup all our temporary readers and swap in our new ones
private void replaceWithFinishedReaders(List finished)
{
if (isOffline)
{
for (SSTableReader reader : discard)
{
if (reader.getCurrentReplacement() == null)
reader.markObsolete();
reader.sharedRef().release();
}
}
else
{
dataTracker.replaceEarlyOpenedFiles(discard, finished);
dataTracker.unmarkCompacting(discard);
}
discard.clear();
}
private static final class Finished
{
final SSTableWriter writer;
final SSTableReader reader;
private Finished(SSTableWriter writer, SSTableReader reader)
{
this.writer = writer;
this.reader = reader;
}
}
}
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