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 Detail

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