org.rocksdb

Class HyperClockCache

java.lang.Object

org.rocksdb.AbstractNativeReference

org.rocksdb.AbstractImmutableNativeReference

org.rocksdb.RocksObject

org.rocksdb.Cache

org.rocksdb.HyperClockCache

All Implemented Interfaces:

java.lang.AutoCloseable

@Experimental(value="HyperClockCache is still experimental and this API may change in future.")
public class HyperClockCache
extends Cache

HyperClockCache - A lock-free Cache alternative for RocksDB block cache that offers much improved CPU efficiency vs. LRUCache under high parallel load or high contention, with some caveats:

• Not a general Cache implementation: can only be used for BlockBasedTableOptions::block_cache, which RocksDB uses in a way that is compatible with HyperClockCache.
• Requires an extra tuning parameter: see estimated_entry_charge below. Similarly, substantially changing the capacity with SetCapacity could harm efficiency. -> EXPERIMENTAL: the tuning parameter can be set to 0 to find the appropriate balance automatically.
• Cache priorities are less aggressively enforced, which could cause cache dilution from long range scans (unless they use fill_cache=false).
• Can be worse for small caches, because if almost all of a cache shard is pinned (more likely with non-partitioned filters), then CLOCK eviction becomes very CPU intensive.

Field Summary

Fields inherited from class org.rocksdb.RocksObject

nativeHandle_

Fields inherited from class org.rocksdb.AbstractImmutableNativeReference

owningHandle_

Constructor Summary

Constructors

Constructor and Description
HyperClockCache(long capacity, long estimatedEntryCharge, int numShardBits, boolean strictCapacityLimit)

Method Summary

Modifier and Type	Method and Description
protected void	disposeInternal(long handle)

Methods inherited from class org.rocksdb.Cache

getPinnedUsage, getUsage

Methods inherited from class org.rocksdb.RocksObject

disposeInternal, getNativeHandle

Methods inherited from class org.rocksdb.AbstractImmutableNativeReference

close, disOwnNativeHandle, isOwningHandle

Methods inherited from class java.lang.Object

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

Constructor Detail

HyperClockCache

public HyperClockCache(long capacity,
                       long estimatedEntryCharge,
                       int numShardBits,
                       boolean strictCapacityLimit)

Parameters:

capacity - The fixed size capacity of the cache

estimatedEntryCharge - EXPERIMENTAL: the field can be set to 0 to size the table dynamically and automatically. See C++ Api for more info.

numShardBits - The cache is sharded to 2^numShardBits shards, by hash of the key

strictCapacityLimit - insert to the cache will fail when cache is full

Method Detail

disposeInternal

protected void disposeInternal(long handle)

Specified by:

disposeInternal in class RocksObject