org.apache.cassandra.index.sai.disk.v1.postings.PostingListRangeIterator Maven / Gradle / Ivy
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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.index.sai.disk.v1.postings;
import java.io.IOException;
import java.util.Arrays;
import java.util.concurrent.TimeUnit;
import javax.annotation.concurrent.NotThreadSafe;
import com.google.common.base.Stopwatch;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.exceptions.QueryCancelledException;
import org.apache.cassandra.index.sai.QueryContext;
import org.apache.cassandra.index.sai.disk.PrimaryKeyMap;
import org.apache.cassandra.index.sai.utils.IndexIdentifier;
import org.apache.cassandra.index.sai.disk.v1.segment.IndexSegmentSearcherContext;
import org.apache.cassandra.index.sai.iterators.KeyRangeIterator;
import org.apache.cassandra.index.sai.postings.PostingList;
import org.apache.cassandra.index.sai.utils.PrimaryKey;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.utils.Throwables;
/**
* A key iterator based on a {@link PostingList} derived from a single index segment.
*
*
* - fetch next segment row id from posting list or skip to specific segment row id if {@link #skipTo(PrimaryKey)} is called
* - add {@link IndexSegmentSearcherContext#segmentRowIdOffset} to obtain the sstable row id
* - produce a {@link PrimaryKey} from {@link PrimaryKeyMap#primaryKeyFromRowId(long)} which is used
* to avoid fetching duplicated keys due to partition-level indexing on wide partition schema.
*
* Note: in order to reduce disk access in multi-index query, partition keys will only be fetched for intersected tokens
* in {@link org.apache.cassandra.index.sai.plan.StorageAttachedIndexSearcher}.
*
*
*
*/
@NotThreadSafe
public class PostingListRangeIterator extends KeyRangeIterator
{
private static final Logger logger = LoggerFactory.getLogger(PostingListRangeIterator.class);
private final Stopwatch timeToExhaust = Stopwatch.createStarted();
private final QueryContext queryContext;
private final PostingList postingList;
private final IndexIdentifier indexIdentifier;
private final PrimaryKeyMap primaryKeyMap;
private final long rowIdOffset;
private boolean needsSkipping = false;
private PrimaryKey skipToKey = null;
/**
* Create a direct PostingListRangeIterator where the underlying PostingList is materialised
* immediately so the posting list size can be used.
*/
public PostingListRangeIterator(IndexIdentifier indexIdentifier,
PrimaryKeyMap primaryKeyMap,
IndexSegmentSearcherContext searcherContext)
{
super(searcherContext.minimumKey, searcherContext.maximumKey, searcherContext.count());
this.indexIdentifier = indexIdentifier;
this.primaryKeyMap = primaryKeyMap;
this.postingList = searcherContext.postingList;
this.rowIdOffset = searcherContext.segmentRowIdOffset;
this.queryContext = searcherContext.context;
}
@Override
protected void performSkipTo(PrimaryKey nextKey)
{
if (skipToKey != null && skipToKey.compareTo(nextKey) > 0)
return;
skipToKey = nextKey;
needsSkipping = true;
}
@Override
protected PrimaryKey computeNext()
{
try
{
queryContext.checkpoint();
// just end the iterator if we don't have a postingList or current segment is skipped
if (exhausted())
return endOfData();
long rowId = getNextRowId();
if (rowId == PostingList.END_OF_STREAM)
return endOfData();
return primaryKeyMap.primaryKeyFromRowId(rowId);
}
catch (Throwable t)
{
if (!(t instanceof QueryCancelledException))
logger.error(indexIdentifier.logMessage("Unable to provide next token!"), t);
throw Throwables.cleaned(t);
}
}
@Override
public void close()
{
if (logger.isTraceEnabled())
{
final long exhaustedInMills = timeToExhaust.stop().elapsed(TimeUnit.MILLISECONDS);
logger.trace(indexIdentifier.logMessage("PostingListRangeIterator exhausted after {} ms"), exhaustedInMills);
}
FileUtils.closeQuietly(Arrays.asList(postingList, primaryKeyMap));
}
private boolean exhausted()
{
return needsSkipping && skipToKey.compareTo(getMaximum()) > 0;
}
/**
* reads the next sstable row ID from the underlying posting list, potentially skipping to get there.
*/
private long getNextRowId() throws IOException
{
long segmentRowId;
if (needsSkipping)
{
long targetRowID = primaryKeyMap.rowIdFromPrimaryKey(skipToKey);
// skipToToken is larger than max token in token file
if (targetRowID < 0)
{
return PostingList.END_OF_STREAM;
}
segmentRowId = postingList.advance(targetRowID - rowIdOffset);
needsSkipping = false;
}
else
{
segmentRowId = postingList.nextPosting();
}
return segmentRowId != PostingList.END_OF_STREAM
? segmentRowId + rowIdOffset
: PostingList.END_OF_STREAM;
}
}