Package org.apache.storm.metricstore.rocksdb

Class StringMetadataCache

java.lang.Object
org.apache.storm.metricstore.rocksdb.StringMetadataCache
All Implemented Interfaces:
ReadOnlyStringMetadataCache, WritableStringMetadataCache, LruMap.CacheEvictionCallback<String,org.apache.storm.metricstore.rocksdb.StringMetadata>
public class StringMetadataCache extends Object implements LruMap.CacheEvictionCallback<String,org.apache.storm.metricstore.rocksdb.StringMetadata>, WritableStringMetadataCache, ReadOnlyStringMetadataCache
Class to create a use a cache that stores Metadata string information in memory. It allows searching for a Metadata string's unique id, or looking up the string by the unique id. The StringMetadata is stored in an LRU map. When an entry is added to the cache, an older entry may be evicted, which then needs to be immediately stored to the database to provide a consistent view of all the metadata strings.

All write operations adding metadata to RocksDB are done by a single thread (a RocksDbMetricsWriter), but multiple threads can read values from the cache. To clarify which permissions are accessible by various threads, the ReadOnlyStringMetadataCache and WritableStringMetadataCache are provided to be used.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    contains(Integer stringId)
    Determines if a string Id is contained in the cache.
    Set<Map.Entry<String,org.apache.storm.metricstore.rocksdb.StringMetadata>>
    entrySet()
    Get the map of the cache contents.
    void
    evictionCallback(String key, org.apache.storm.metricstore.rocksdb.StringMetadata val)
    Callback when data is about to be removed from the cache.
    org.apache.storm.metricstore.rocksdb.StringMetadata
    get(String s)
    Get the string metadata from the cache.
    String
    getMetadataString(Integer stringId)
    Returns the string matching the string Id if in the cache.
    void
    put(String s, org.apache.storm.metricstore.rocksdb.StringMetadata stringMetadata, boolean newEntry)
    Add the string metadata to the cache.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Method Details

    • get

      public org.apache.storm.metricstore.rocksdb.StringMetadata get(String s)
      Get the string metadata from the cache.
      Specified by:
      get in interface ReadOnlyStringMetadataCache
      Parameters:
      s - The string to look for
      Returns:
      the metadata associated with the string or null if not found

    • put

      public void put(String s, org.apache.storm.metricstore.rocksdb.StringMetadata stringMetadata, boolean newEntry) throws MetricException
      Add the string metadata to the cache.

      NOTE: this can cause data to be evicted from the cache when full. When this occurs, the evictionCallback() method is called to store the metadata back into the RocksDB database.

      This method is only exposed to the WritableStringMetadataCache interface.

      Specified by:
      put in interface WritableStringMetadataCache
      Parameters:
      s - The string to add
      stringMetadata - The string's metadata
      newEntry - Indicates the metadata is being used for the first time and should be written to RocksDB immediately
      Throws:
      MetricException - when evicted data fails to save to the database or when the database is shutdown

    • evictionCallback

      public void evictionCallback(String key, org.apache.storm.metricstore.rocksdb.StringMetadata val)
      Callback when data is about to be removed from the cache. This method then immediately writes the metadata to RocksDB.
      Specified by:
      evictionCallback in interface LruMap.CacheEvictionCallback<String,org.apache.storm.metricstore.rocksdb.StringMetadata>
      Parameters:
      key - The evicted string
      val - The evicted string's metadata
      Throws:
      RuntimeException - when evicted data fails to save to the database

    • contains

      public boolean contains(Integer stringId)
      Determines if a string Id is contained in the cache.
      Specified by:
      contains in interface ReadOnlyStringMetadataCache
      Parameters:
      stringId - The string Id to check
      Returns:
      true if the Id is in the cache, false otherwise

    • getMetadataString

      public String getMetadataString(Integer stringId)
      Returns the string matching the string Id if in the cache.
      Specified by:
      getMetadataString in interface ReadOnlyStringMetadataCache
      Parameters:
      stringId - The string Id to check
      Returns:
      the associated string if the Id is in the cache, null otherwise

    • entrySet

      public Set<Map.Entry<String,org.apache.storm.metricstore.rocksdb.StringMetadata>> entrySet()
      Get the map of the cache contents. Provided to allow writing the data to RocksDB on shutdown.
      Specified by:
      entrySet in interface WritableStringMetadataCache
      Returns:
      the string metadata map entrySet