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https://issues.apache.org/jira/browse/HBASE-11364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14037745#comment-14037745
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stack commented on HBASE-11364:
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[~lhofhansl]
bq. I can see this both way. Since off caching is a separate option your way is
better: Once off heap cache is enabled, data goes there by default.
Come again Lars. I don't follow. Options are:
1. Do NOT enable offheap by default. Just talk it up as the way to go
underlining it will make pure in-memory access slower (but you can make it so
some of your tables are pegged in memory if you want because of the flag here).
Upside: No surprise. Downside: Folks don't read manuals nor change defaults.
2. Enable offheap BucketCache using CombinedBucketCache. When folks upgrade,
latency to user-level DATA blocks will go up. Upsides: less GC, more cached.
Downside: those who notice added latency might get upset. Changing schema will
require alter table.
3. Enable offheap BucketCache but in additive mode where we just add in an L2
under the L1 LruBlockCache. Upside: Additive. Downside: Could make for more
GC.
Of the above, maybe 1. is the way to go? 2. may surprise in that perf and GC
gets better of a sudden (this would be ok) but others may be surprised that
their latencies have gone up for some key tables. 3. may actually make GC
worse (at least that is case in the SlabCache case which is similar and the
L1/L2 layout doesn't get good review to date going by HBASE-8894).
Will test 3.
> [BlockCache] Add a flag to cache data blocks in L1 if multi-tier cache
> ----------------------------------------------------------------------
>
> Key: HBASE-11364
> URL: https://issues.apache.org/jira/browse/HBASE-11364
> Project: HBase
> Issue Type: Task
> Reporter: stack
> Assignee: stack
> Fix For: 0.99.0
>
> Attachments: 11364.txt
>
>
> This is a prerequisite for HBASE-11323 BucketCache on all the time. It
> addresses a @lars hofhansl ask that we be able to ask that for some column
> families, even their data blocks get cached up in the LruBlockCache L1 tier
> in a multi-tier deploy as happens when doing BucketCache (CombinedBlockCache)
> setups.
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