Package org.apache.jackrabbit.oak.cache

Class CacheLIRS<K,V>

java.lang.Object
org.apache.jackrabbit.oak.cache.CacheLIRS<K,V>
Type Parameters:
K - the key type
V - the value type
All Implemented Interfaces:
Function<K,V>, org.apache.jackrabbit.guava.common.base.Function<K,V>, org.apache.jackrabbit.guava.common.cache.Cache<K,V>, org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
@Internal(since="1.1.1") public class CacheLIRS<K,V> extends Object implements org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
For Oak internal use only. Do not use outside Oak components.

A scan resistant cache. It is meant to cache objects that are relatively costly to acquire, for example file content.

This implementation is multi-threading safe and supports concurrent access. Null keys or null values are not allowed. The map fill factor is at most 75%.

Each entry is assigned a distinct memory size, and the cache will try to use at most the specified amount of memory. The memory unit is not relevant, however it is suggested to use bytes as the unit.

This class implements an approximation of the the LIRS replacement algorithm invented by Xiaodong Zhang and Song Jiang as described in http://www.cse.ohio-state.edu/~zhang/lirs-sigmetrics-02.html with a few smaller changes: An additional queue for non-resident entries is used, to prevent unbound memory usage. The maximum size of this queue is at most the size of the rest of the stack. About 6.25% of the mapped entries are cold.

Internally, the cache is split into a number of segments, and each segment is an individual LIRS cache.

Accessed entries are only moved to the top of the stack if at least a number of other entries have been moved to the front (1% by default). Write access and moving entries to the top of the stack is synchronized per segment.

Author:
Thomas Mueller

  • Constructor Details

    • CacheLIRS

      public CacheLIRS(int maxEntries)
      Create a new cache with the given number of entries, and the default settings (an average size of 1 per entry, 16 segments, and stack move distance equals to the maximum number of entries divided by 100).
      Parameters:
      maxEntries - the maximum number of entries

  • Method Details

    • invalidateAll

      public void invalidateAll()
      Remove all entries.
      Specified by:
      invalidateAll in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • containsKey

      public boolean containsKey(Object key)
      Check whether there is a resident entry for the given key. This method does not adjust the internal state of the cache.
      Parameters:
      key - the key (may not be null)
      Returns:
      true if there is a resident entry

    • peek

      public V peek(K key)
      Get the value for the given key if the entry is cached. This method does not modify the internal state.
      Parameters:
      key - the key (may not be null)
      Returns:
      the value, or null if there is no resident entry

    • put

      public V put(K key, V value, int memory)
      Add an entry to the cache. This method is an explicit memory size (weight), and not using the weigher even if configured. The entry may or may not exist in the cache yet. This method will usually mark unknown entries as cold and known entries as hot.
      Parameters:
      key - the key (may not be null)
      value - the value (may not be null)
      memory - the memory used for the given entry
      Returns:
      the old value, or null if there was no resident entry

    • put

      public void put(K key, V value)
      Add an entry to the cache. If a weigher is specified, it is used, otherwise the average memory size is used.
      Specified by:
      put in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Parameters:
      key - the key (may not be null)
      value - the value (may not be null)

    • get

      public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException
      Specified by:
      get in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Throws:
      ExecutionException

    • getUnchecked

      public V getUnchecked(K key)
      Get the value, loading it if needed.

      If there is an exception loading, an UncheckedExecutionException is thrown.

      Specified by:
      getUnchecked in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
      Parameters:
      key - the key
      Returns:
      the value
      Throws:
      org.apache.jackrabbit.guava.common.util.concurrent.UncheckedExecutionException

    • get

      public V get(K key) throws ExecutionException
      Get the value, loading it if needed.
      Specified by:
      get in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
      Parameters:
      key - the key
      Returns:
      the value
      Throws:
      ExecutionException

    • refresh

      public void refresh(K key)
      Re-load the value for the given key.

      If there is an exception while loading, it is logged and ignored. This method calls CacheLoader.reload, but synchronously replaces the old value.

      Specified by:
      refresh in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
      Parameters:
      key - the key

    • putIfAbsent

      protected V putIfAbsent(K key, V value)

    • getIfPresent

      @Nullable public V getIfPresent(Object key)
      Get the value for the given key if the entry is cached. This method adjusts the internal state of the cache sometimes, to ensure commonly used entries stay in the cache.
      Specified by:
      getIfPresent in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Parameters:
      key - the key (may not be null)
      Returns:
      the value, or null if there is no resident entry

    • sizeOf

      protected int sizeOf(K key, V value)
      Get the size of the given value. The default implementation returns the average memory as configured for this cache.
      Parameters:
      key - the key
      value - the value
      Returns:
      the size

    • invalidate

      public void invalidate(Object key)
      Remove an entry. Both resident and non-resident entries can be removed.
      Specified by:
      invalidate in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Parameters:
      key - the key (may not be null)

    • remove

      public V remove(Object key)
      Remove an entry. Both resident and non-resident entries can be removed.
      Parameters:
      key - the key (may not be null)
      Returns:
      the old value or null

    • invalidateAll

      public void invalidateAll(Iterable<?> keys)
      Specified by:
      invalidateAll in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • getMemory

      public int getMemory(K key)
      Get the memory used for the given key.
      Parameters:
      key - the key (may not be null)
      Returns:
      the memory, or 0 if there is no resident entry

    • getUsedMemory

      public long getUsedMemory()
      Get the currently used memory.
      Returns:
      the used memory

    • setMaxMemory

      public void setMaxMemory(long maxMemory)
      Set the maximum memory this cache should use. This will not immediately cause entries to get removed however; it will only change the limit. To resize the internal array, call the clear method.
      Parameters:
      maxMemory - the maximum size (1 or larger)

    • setAverageMemory

      public void setAverageMemory(int averageMemory)
      Set the average memory used per entry. It is used to calculate the length of the internal array.
      Parameters:
      averageMemory - the average memory used (1 or larger)

    • getAverageMemory

      public int getAverageMemory()
      Get the average memory used per entry.
      Returns:
      the average memory

    • getMaxMemory

      public long getMaxMemory()
      Get the maximum memory to use.
      Returns:
      the maximum memory

    • entrySet

      public Set<Map.Entry<K,V>> entrySet()
      Get the entry set for all resident entries.
      Returns:
      the entry set

    • values

      protected Collection<V> values()

    • keySet

      public Set<K> keySet()
      Get the set of keys for resident entries.
      Returns:
      the set of keys

    • sizeNonResident

      public int sizeNonResident()
      Get the number of non-resident entries in the cache.
      Returns:
      the number of non-resident entries

    • sizeMapArray

      public int sizeMapArray()
      Get the length of the internal map array.
      Returns:
      the size of the array

    • sizeHot

      public int sizeHot()
      Get the number of hot entries in the cache.
      Returns:
      the number of hot entries

    • size

      public long size()
      Get the number of resident entries.
      Specified by:
      size in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Returns:
      the number of entries

    • keys

      public List<K> keys(boolean cold, boolean nonResident)
      Get the list of keys. This method allows to read the internal state of the cache.
      Parameters:
      cold - if true, only keys for the cold entries are returned
      nonResident - true for non-resident entries
      Returns:
      the key list

    • stats

      public org.apache.jackrabbit.guava.common.cache.CacheStats stats()
      Specified by:
      stats in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • newBuilder

      public static <K, V> CacheLIRS.Builder<K,V> newBuilder()
      Create a builder.
      Returns:
      the builder

    • getAllPresent

      public org.apache.jackrabbit.guava.common.collect.ImmutableMap<K,V> getAllPresent(Iterable<?> keys)
      Specified by:
      getAllPresent in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • asMap

      public ConcurrentMap<K,V> asMap()
      Specified by:
      asMap in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>
      Specified by:
      asMap in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>

    • cleanUp

      public void cleanUp()
      Specified by:
      cleanUp in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • putAll

      public void putAll(Map<? extends K,? extends V> m)
      Specified by:
      putAll in interface org.apache.jackrabbit.guava.common.cache.Cache<K,V>

    • getAll

      public org.apache.jackrabbit.guava.common.collect.ImmutableMap<K,V> getAll(Iterable<? extends K> keys) throws ExecutionException
      Specified by:
      getAll in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>
      Throws:
      ExecutionException

    • apply

      public V apply(K key)
      Specified by:
      apply in interface Function<K,V>
      Specified by:
      apply in interface org.apache.jackrabbit.guava.common.base.Function<K,V>
      Specified by:
      apply in interface org.apache.jackrabbit.guava.common.cache.LoadingCache<K,V>

    • isEmpty

      public boolean isEmpty()