[Amemeda]

LruBlockCache was deprecated in #4920 and replaced with TinyLfuBlockCache, this pr removes LruBlockCache and related code:

• LruBlockCache.java: Deleted
• LruBlockCacheConfiguration.java: Deleted
• LruBlockCacheManager.java: Deleted
• TestlLruBlockCache.java: Deleted
• BlockCacheFactoryTest: Updated to remove deprecated test testCreateLruBlockCacheFactory()
• CachedBlock.java: Deleted (only uses were in deleted test file)
• CacheBlockQueue.java: Deleted (only uses were in deleted test file)
• HeapSize.java: Deleted (only uses were in deleted test file)
• TestCachedBlockQueue: Deleted, only tested lru cache using the above 3 files
• SynchronizedLoadingBlockCache.java: Deleted
• blockfile.cache.lru subfolder: Emptied and deleted

Closes #4921

[Amemeda]

There are 4 files remaining in the cache.lru subfolder where all the lru files were deleted from. The only usage of these files is in TestCachedBlockQueue.java which is testing using lru.CachedBlock.java. All tests in this file still pass with the LRU deleted. So I am wondering, should TestCachedBlockQueue.java be deleted along with the remaining 4 files in lru package? Or I can refactor the remaining 4 files from the lru package, probably to rename the package to util or something similar.

[dlmarion]

I think you can remove TestCachedBlockQueue as well

[Amemeda]

There is a method in BlockCacheManager.java that still has documentation referencing LRU. Unsure if this needs to be updated to TinyLFU or its talking about a different LRU like the LRU Map I see throughout the code

   /**
     * This method provides a way for a cache implementation to access arbitrary configuration set
     * by a user.
     *
     * <p>
     * When running in a tserver, returns all Accumulo properties that have a prefix of
     * {@code tserver.cache.config.<prefix>.<type>.} or
     * {@code tserver.cache.config.<prefix>.default.} with values for specific cache types
     * overriding defaults.
     *
     * <p>
     * When running in a scan server, returns all Accumulo properties that have a prefix of
     * {@code sserver.cache.config.<prefix>.<type>.} or
     * {@code sserver.cache.config.<prefix>.default.} with values for specific cache types
     * overriding defaults.
     *
     * <p>
     * For example assume the following data is in Accumulo's system config and the plugin is
     * running in a tserver.
     *
     * <pre>
     * tserver.cache.config.lru.default.evictAfter=3600
     * tserver.cache.config.lru.default.loadFactor=.75
     * tserver.cache.config.lru.index.loadFactor=.55
     * tserver.cache.config.lru.data.loadFactor=.65
     * </pre>
     *
     * <p>
     * If this method is called with {@code prefix=lru} and {@code type=INDEX} then it would return
     * a map with the following key values. The load factor setting for index overrides the default
     * value.
     *
     * <pre>
     * evictAfter=3600
     * loadFactor=.55
     * </pre>
     *
     * @param prefix A unique identifier that corresponds to a particular BlockCacheManager
     *        implementation.
     */
    Map<String,String> getProperties(String prefix, CacheType type);

[dlmarion]

@Amemeda - can you merge main into this branch to get it up to date. Then I'll merge it.

[DomGarguilo]

SynchronizedLoadingBlockCache.java: Moved to spi.cache subfolder. Still used elsewhere in code.

I can't find where else its used in the code? I don't think moving it into spi.cache is a good idea since that makes it public API. Could we just delete it instead?

[DomGarguilo]

There is a method in BlockCacheManager.java that still has documentation referencing LRU. Unsure if this needs to be updated to TinyLFU or its talking about a different LRU like the LRU Map I see throughout the code

Yea I think this should be updated. Maybe just swap the example to use a generic prefix like tserver.cache.config.myplugin.default.* with prefix=myplugin for example.

[DomGarguilo]

Users who have general.block.cache.manager.class set to LruBlockCacheManager will fail to start after upgrading to 4.0. Could we add a release note telling them to unset the property or switch to TinyLfuBlockCacheManager?

[Amemeda]

I can't find where else its used in the code? I don't think moving it into spi.cache is a good idea since that makes it public API. Could we just delete it instead?

SynchronizedLoadingBlochCache has no usages, but it is referenced in BlockCache.getBlock documentation, so I was assuming it was still usable, I will still remove it for now

 /**
   * This method allows a cache to prevent concurrent loads of the same block. However a cache
   * implementation is not required to prevent concurrent loads.
   * {@link SynchronousLoadingBlockCache} is an abstract class that a cache can extent which does
   * prevent concurrent loading of the same block.
   *
   *
   * @param blockName Block name to fetch
   * @param loader If the block is not present in the cache, the loader can be called to load it.
   * @return Block or null if block is not in the cache or didn't load.
   */
  CacheEntry getBlock(String blockName, Loader loader);