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https://issues.apache.org/jira/browse/HBASE-9553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13769161#comment-13769161
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Liang Xie commented on HBASE-9553:
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probably it could beat the current implement:) but imho, the off-heap
solution(e.g. bucket cache with off-heap enabled) is still better than padding.
per one of our internal benchmark, the off-heap block caching model could cut
off the "99% pencentile latency" to a half, comparing the current on-heap block
caching implement.
ps: i remembered(unclear) hotspot internal could dynamically resize some stuff,
like PLAB, to meet the diff obj sizes. maybe some vm expects could give more
explaination:) of cause, i agree, the change from app code would be better than
depends on hotspot:)
> Pad HFile blocks to a fixed size before placing them into the blockcache
> ------------------------------------------------------------------------
>
> Key: HBASE-9553
> URL: https://issues.apache.org/jira/browse/HBASE-9553
> Project: HBase
> Issue Type: Bug
> Reporter: Lars Hofhansl
>
> In order to make it easy on the garbage collector and to avoid full
> compaction phases we should make sure that all (or at least a large
> percentage) of the HFile blocks as cached in the block cache are exactly the
> same size.
> Currently an HFile block is typically slightly larger than the declared block
> size, as the block will accommodate that last KV on the block. The padding
> would be a ColumnFamily option. In many cases 100 bytes would probably be a
> good value to make all blocks exactly the same size (but of course it depends
> on the max size of the KVs).
> This does not have to be perfect. The more blocks evicted and replaced in the
> block cache are of the exact same size the easier it should be on the GC.
> Thoughts?
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