Module org.eclipse.jgit
Package org.eclipse.jgit.internal.storage.dfs

Class DfsBlockCache

java.lang.Object
org.eclipse.jgit.internal.storage.dfs.DfsBlockCache
public final class DfsBlockCache extends Object
Caches slices of a BlockBasedFile in memory for faster read access.

The DfsBlockCache serves as a Java based "buffer cache", loading segments of a BlockBasedFile into the JVM heap prior to use. As JGit often wants to do reads of only tiny slices of a file, the DfsBlockCache tries to smooth out these tiny reads into larger block-sized IO operations.

Its too expensive during object access to be accurate with a least recently used (LRU) algorithm. Strictly ordering every read is a lot of overhead that typically doesn't yield a corresponding benefit to the application.

The key tuple is passed through to methods as a pair of parameters rather than as a single Object, thus reducing the transient memory allocations of callers. It is more efficient to avoid the allocation, as we can't be 100% sure that a JIT would be able to stack-allocate a key tuple.

  • Method Details

    • reconfigure

      public static void reconfigure(DfsBlockCacheConfig cfg)
      Modify the configuration of the window cache.

      The new configuration is applied immediately, and the existing cache is cleared.

      Parameters:
      cfg - the new window cache configuration.
      Throws:
      IllegalArgumentException - the cache configuration contains one or more invalid settings, usually too low of a limit.

    • getInstance

      public static DfsBlockCache getInstance()
      Get the currently active DfsBlockCache.
      Returns:
      the currently active DfsBlockCache.

    • getCurrentSize

      public long[] getCurrentSize()
      Get total number of bytes in the cache, per pack file extension.
      Returns:
      total number of bytes in the cache, per pack file extension.

    • getFillPercentage

      public long getFillPercentage()
      Get 0..100, defining how full the cache is.
      Returns:
      0..100, defining how full the cache is.

    • getHitCount

      public long[] getHitCount()
      Get number of requests for items in the cache, per pack file extension.
      Returns:
      number of requests for items in the cache, per pack file extension.

    • getMissCount

      public long[] getMissCount()
      Get number of requests for items not in the cache, per pack file extension.
      Returns:
      number of requests for items not in the cache, per pack file extension.

    • getTotalRequestCount

      public long[] getTotalRequestCount()
      Get total number of requests (hit + miss), per pack file extension.
      Returns:
      total number of requests (hit + miss), per pack file extension.

    • getHitRatio

      public long[] getHitRatio()
      Get hit ratios
      Returns:
      hit ratios

    • getEvictions

      public long[] getEvictions()
      Get number of evictions performed due to cache being full, per pack file extension.
      Returns:
      number of evictions performed due to cache being full, per pack file extension.

    • getAllBlockCacheStats

      public List<DfsBlockCacheTable.BlockCacheStats> getAllBlockCacheStats()
      Get the list of DfsBlockCacheTable.BlockCacheStats for all underlying caches.

      Useful in monitoring caches with breakdown.

      Returns:
      the list of DfsBlockCacheTable.BlockCacheStats for all underlying caches.

    • hasBlock0

      public boolean hasBlock0(DfsStreamKey key)
      Quickly check if the cache contains block 0 of the given stream.

      This can be useful for sophisticated pre-read algorithms to quickly determine if a file is likely already in cache, especially small reftables which may be smaller than a typical DFS block size.

      Parameters:
      key - the file to check.
      Returns:
      true if block 0 (the first block) is in the cache.