com.metamx.druid.client.cache.MemcachedCache.java Source code

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Here is the source code for com.metamx.druid.client.cache.MemcachedCache.java

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/*
 * Druid - a distributed column store.
 * Copyright (C) 2012  Metamarkets Group Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

package com.metamx.druid.client.cache;

import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.base.Throwables;
import com.google.common.collect.Maps;
import com.google.common.primitives.Ints;
import com.metamx.common.logger.Logger;
import net.spy.memcached.AddrUtil;
import net.spy.memcached.ConnectionFactoryBuilder;
import net.spy.memcached.DefaultHashAlgorithm;
import net.spy.memcached.FailureMode;
import net.spy.memcached.MemcachedClient;
import net.spy.memcached.MemcachedClientIF;
import net.spy.memcached.internal.BulkFuture;
import net.spy.memcached.transcoders.SerializingTranscoder;
import org.apache.commons.codec.digest.DigestUtils;

import javax.annotation.Nullable;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.Map;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicLong;

public class MemcachedCache implements Cache {
    private static final Logger log = new Logger(MemcachedCache.class);

    public static MemcachedCache create(final MemcachedCacheConfig config) {
        try {
            LZ4Transcoder transcoder = new LZ4Transcoder(config.getMaxObjectSize());

            // always use compression
            transcoder.setCompressionThreshold(0);

            return new MemcachedCache(new MemcachedClient(
                    new ConnectionFactoryBuilder().setProtocol(ConnectionFactoryBuilder.Protocol.BINARY)
                            .setHashAlg(DefaultHashAlgorithm.FNV1A_64_HASH)
                            .setLocatorType(ConnectionFactoryBuilder.Locator.CONSISTENT).setDaemon(true)
                            .setFailureMode(FailureMode.Cancel).setTranscoder(transcoder).setShouldOptimize(true)
                            .setOpQueueMaxBlockTime(config.getTimeout()).setOpTimeout(config.getTimeout()).build(),
                    AddrUtil.getAddresses(config.getHosts())), config.getMemcachedPrefix(), config.getTimeout(),
                    config.getExpiration());
        } catch (IOException e) {
            throw Throwables.propagate(e);
        }
    }

    private final int timeout;
    private final int expiration;
    private final String memcachedPrefix;

    private final MemcachedClientIF client;

    private final AtomicLong hitCount = new AtomicLong(0);
    private final AtomicLong missCount = new AtomicLong(0);
    private final AtomicLong timeoutCount = new AtomicLong(0);
    private final AtomicLong errorCount = new AtomicLong(0);

    MemcachedCache(MemcachedClientIF client, String memcachedPrefix, int timeout, int expiration) {
        Preconditions.checkArgument(memcachedPrefix.length() <= MAX_PREFIX_LENGTH,
                "memcachedPrefix length [%d] exceeds maximum length [%d]", memcachedPrefix.length(),
                MAX_PREFIX_LENGTH);
        this.timeout = timeout;
        this.expiration = expiration;
        this.client = client;
        this.memcachedPrefix = memcachedPrefix;
    }

    @Override
    public CacheStats getStats() {
        return new CacheStats(hitCount.get(), missCount.get(), 0, 0, 0, timeoutCount.get(), errorCount.get());
    }

    @Override
    public byte[] get(NamedKey key) {
        Future<Object> future;
        try {
            future = client.asyncGet(computeKeyHash(memcachedPrefix, key));
        } catch (IllegalStateException e) {
            // operation did not get queued in time (queue is full)
            errorCount.incrementAndGet();
            log.warn(e, "Unable to queue cache operation");
            return null;
        }
        try {
            byte[] bytes = (byte[]) future.get(timeout, TimeUnit.MILLISECONDS);
            if (bytes != null) {
                hitCount.incrementAndGet();
            } else {
                missCount.incrementAndGet();
            }
            return bytes == null ? null : deserializeValue(key, bytes);
        } catch (TimeoutException e) {
            timeoutCount.incrementAndGet();
            future.cancel(false);
            return null;
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw Throwables.propagate(e);
        } catch (ExecutionException e) {
            errorCount.incrementAndGet();
            log.warn(e, "Exception pulling item from cache");
            return null;
        }
    }

    @Override
    public void put(NamedKey key, byte[] value) {
        try {
            client.set(computeKeyHash(memcachedPrefix, key), expiration, serializeValue(key, value));
        } catch (IllegalStateException e) {
            // operation did not get queued in time (queue is full)
            errorCount.incrementAndGet();
            log.warn(e, "Unable to queue cache operation");
        }
    }

    private static byte[] serializeValue(NamedKey key, byte[] value) {
        byte[] keyBytes = key.toByteArray();
        return ByteBuffer.allocate(Ints.BYTES + keyBytes.length + value.length).putInt(keyBytes.length)
                .put(keyBytes).put(value).array();
    }

    private static byte[] deserializeValue(NamedKey key, byte[] bytes) {
        ByteBuffer buf = ByteBuffer.wrap(bytes);

        final int keyLength = buf.getInt();
        byte[] keyBytes = new byte[keyLength];
        buf.get(keyBytes);
        byte[] value = new byte[buf.remaining()];
        buf.get(value);

        Preconditions.checkState(Arrays.equals(keyBytes, key.toByteArray()),
                "Keys do not match, possible hash collision?");
        return value;
    }

    @Override
    public Map<NamedKey, byte[]> getBulk(Iterable<NamedKey> keys) {
        Map<String, NamedKey> keyLookup = Maps.uniqueIndex(keys, new Function<NamedKey, String>() {
            @Override
            public String apply(@Nullable NamedKey input) {
                return computeKeyHash(memcachedPrefix, input);
            }
        });

        Map<NamedKey, byte[]> results = Maps.newHashMap();

        BulkFuture<Map<String, Object>> future;
        try {
            future = client.asyncGetBulk(keyLookup.keySet());
        } catch (IllegalStateException e) {
            // operation did not get queued in time (queue is full)
            errorCount.incrementAndGet();
            log.warn(e, "Unable to queue cache operation");
            return results;
        }

        try {
            Map<String, Object> some = future.getSome(timeout, TimeUnit.MILLISECONDS);

            if (future.isTimeout()) {
                future.cancel(false);
                timeoutCount.incrementAndGet();
            }
            missCount.addAndGet(keyLookup.size() - some.size());
            hitCount.addAndGet(some.size());

            for (Map.Entry<String, Object> entry : some.entrySet()) {
                final NamedKey key = keyLookup.get(entry.getKey());
                final byte[] value = (byte[]) entry.getValue();
                results.put(key, value == null ? null : deserializeValue(key, value));
            }

            return results;
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw Throwables.propagate(e);
        } catch (ExecutionException e) {
            errorCount.incrementAndGet();
            log.warn(e, "Exception pulling item from cache");
            return results;
        }
    }

    @Override
    public void close(String namespace) {
        // no resources to cleanup
    }

    public static final int MAX_PREFIX_LENGTH = MemcachedClientIF.MAX_KEY_LENGTH - 40 // length of namespace hash
            - 40 // length of key hash
            - 2 // length of separators
    ;

    private static String computeKeyHash(String memcachedPrefix, NamedKey key) {
        // hash keys to keep things under 250 characters for memcached
        return memcachedPrefix + ":" + DigestUtils.sha1Hex(key.namespace) + ":" + DigestUtils.sha1Hex(key.key);
    }
}