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| <h1 title="Package" class="title">Package org.apache.hadoop.hbase.io.hfile</h1> |
| <div class="docSummary"> |
| <div class="block">Provides implementations of <code>HFile</code> and HFile |
| <code>BlockCache</code>.</div> |
| </div> |
| <p>See: <a href="#package.description">Description</a></p> |
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| <h2 title="Package org.apache.hadoop.hbase.io.hfile Description">Package org.apache.hadoop.hbase.io.hfile Description</h2> |
| <div class="block">Provides implementations of <code>HFile</code> and HFile |
| <code>BlockCache</code>. Caches are configured (and instantiated) |
| by <code>CacheConfig</code>. See head of the |
| <code>CacheConfig</code> class for constants that define |
| cache options and configuration keys to use setting cache options. Cache implementations |
| include the default, native on-heap <code>LruBlockCache</code> and a |
| <code>BucketCache</code> that has a bunch of deploy formats |
| including acting as a L2 for LruBlockCache -- when a block is evicted from LruBlockCache, it |
| goes to the BucketCache and when we search a block, we look in both places -- or, the |
| most common deploy type, |
| using <code>CombinedBlockCache</code>, BucketCache is used as |
| a host for data blocks with meta blocks in an instance of LruBlockCache. BucketCache |
| can also be onheap, offheap, and file-backed. |
| |
| <h1>Which BlockCache should I use?</h1> |
| By default LruBlockCache is on. If you would like to cache more, and offheap (offheap |
| usually means less GC headache), try enabling * BucketCache. Fetching will always |
| be slower when fetching from BucketCache but latencies tend to be less erratic over time |
| (roughly because GC is less). See Nick Dimiduk's |
| <a href="http://www.n10k.com/blog/blockcache-101/">BlockCache 101</a> for some numbers. |
| |
| <h1>Enabling <code>BucketCache</code></h1> |
| See the HBase Reference Guide <a href="http://hbase.apache.org/book.html#enable.bucketcache">Enable BucketCache</a>.</div> |
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