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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
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* 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,
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package org.apache.cassandra.db;
import java.util.*;
import java.util.concurrent.TimeUnit;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.db.lifecycle.SSTableIntervalTree;
import org.apache.cassandra.db.lifecycle.SSTableSet;
import org.apache.cassandra.db.lifecycle.View;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.locator.TokenMetadata;
import org.apache.cassandra.schema.Schema;
import org.apache.cassandra.schema.SchemaChangeListener;
import org.apache.cassandra.schema.TableMetadata;
import org.apache.cassandra.service.StorageService;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.Pair;
import org.apache.cassandra.utils.concurrent.Refs;
import static org.apache.cassandra.utils.Clock.Global.nanoTime;
/**
* A very simplistic/crude partition count/size estimator.
*
* Exposing per-primary-range estimated partitions count and size in CQL form.
*
* Estimates (per primary range) are calculated and dumped into a system table (system.size_estimates) every 5 minutes.
*
* See CASSANDRA-7688.
*/
public class SizeEstimatesRecorder implements SchemaChangeListener, Runnable
{
private static final Logger logger = LoggerFactory.getLogger(SizeEstimatesRecorder.class);
public static final SizeEstimatesRecorder instance = new SizeEstimatesRecorder();
private SizeEstimatesRecorder()
{
Schema.instance.registerListener(this);
}
public void run()
{
TokenMetadata metadata = StorageService.instance.getTokenMetadata().cloneOnlyTokenMap();
if (!metadata.isMember(FBUtilities.getBroadcastAddressAndPort()))
{
logger.debug("Node is not part of the ring; not recording size estimates");
return;
}
logger.trace("Recording size estimates");
for (Keyspace keyspace : Keyspace.nonLocalStrategy())
{
// In tools the call to describe_splits_ex() used to be coupled with the call to describe_local_ring() so
// most access was for the local primary range; after creating the size_estimates table this was changed
// to be the primary range.
// In a multi-dc setup its not uncommon for the local ring to be offset by 1 for the next DC; example:
// DC1: [0, 10, 20, 30]
// DC2: [1, 11, 21, 31]
// DC3: [2, 12, 22, 32]
// When working with the primary ring we have:
// [0, 1, 2, 10, 11, 12, 20, 21, 22, 30, 31, 32]
// this then leads to primrary ranges with one token in it, which cause the estimates to be less useful.
// Since only one range was published some tools make this assumption; for this reason we can't publish
// all ranges (including the replica ranges) nor can we keep backwards compatability and publish primary
// range. If we publish multiple ranges downstream integrations may start to see duplicate data.
// See CASSANDRA-15637
Collection> primaryRanges = StorageService.instance.getPrimaryRanges(keyspace.getName());
Collection> localPrimaryRanges = StorageService.instance.getLocalPrimaryRange();
boolean rangesAreEqual = primaryRanges.equals(localPrimaryRanges);
for (ColumnFamilyStore table : keyspace.getColumnFamilyStores())
{
long start = nanoTime();
// compute estimates for primary ranges for backwards compatability
Map, Pair> estimates = computeSizeEstimates(table, primaryRanges);
SystemKeyspace.updateSizeEstimates(table.metadata.keyspace, table.metadata.name, estimates);
SystemKeyspace.updateTableEstimates(table.metadata.keyspace, table.metadata.name, SystemKeyspace.TABLE_ESTIMATES_TYPE_PRIMARY, estimates);
if (!rangesAreEqual)
{
// compute estimate for local primary range
estimates = computeSizeEstimates(table, localPrimaryRanges);
}
SystemKeyspace.updateTableEstimates(table.metadata.keyspace, table.metadata.name, SystemKeyspace.TABLE_ESTIMATES_TYPE_LOCAL_PRIMARY, estimates);
long passed = nanoTime() - start;
if (logger.isTraceEnabled())
logger.trace("Spent {} milliseconds on estimating {}.{} size",
TimeUnit.NANOSECONDS.toMillis(passed),
table.metadata.keyspace,
table.metadata.name);
}
}
}
private static Map, Pair> computeSizeEstimates(ColumnFamilyStore table, Collection> ranges)
{
// for each local primary range, estimate (crudely) mean partition size and partitions count.
Map, Pair> estimates = new HashMap<>(ranges.size());
for (Range localRange : ranges)
{
for (Range unwrappedRange : localRange.unwrap())
{
// filter sstables that have partitions in this range.
Refs refs = null;
long partitionsCount, meanPartitionSize;
try
{
while (refs == null)
{
Iterable sstables = table.getTracker().getView().select(SSTableSet.CANONICAL);
SSTableIntervalTree tree = SSTableIntervalTree.build(sstables);
Range r = Range.makeRowRange(unwrappedRange);
Iterable canonicalSSTables = View.sstablesInBounds(r.left, r.right, tree);
refs = Refs.tryRef(canonicalSSTables);
}
// calculate the estimates.
partitionsCount = estimatePartitionsCount(refs, unwrappedRange);
meanPartitionSize = estimateMeanPartitionSize(refs);
}
finally
{
if (refs != null)
refs.release();
}
estimates.put(unwrappedRange, Pair.create(partitionsCount, meanPartitionSize));
}
}
return estimates;
}
private static long estimatePartitionsCount(Collection sstables, Range range)
{
long count = 0;
for (SSTableReader sstable : sstables)
count += sstable.estimatedKeysForRanges(Collections.singleton(range));
return count;
}
private static long estimateMeanPartitionSize(Collection sstables)
{
long sum = 0, count = 0;
for (SSTableReader sstable : sstables)
{
long n = sstable.getEstimatedPartitionSize().count();
sum += sstable.getEstimatedPartitionSize().mean() * n;
count += n;
}
return count > 0 ? sum / count : 0;
}
@Override
public void onDropTable(TableMetadata table, boolean dropData)
{
SystemKeyspace.clearEstimates(table.keyspace, table.name);
}
}