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https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12878406#action_12878406
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HBase Review Board commented on HBASE-2468:
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Ship it!
+1
I did a quick skim. All looks good. This is a weird one in that to prewarm we
are going to do a getClosestOrBefore (which we'll be doing anyway) and then
we'll open scanner, and scan next 10 rows... then close scanner; i.e. extra
rpcs inline w/ first lookup against tale. This latter will actually slow down
first lookup some but we can make it faster by making open scanner return
results so we don't have to then go call next (already an issue to do this) and
also, making it so we scan forward always by changing keys in .META. such that
region names are keyed by endkey rather than startkey... also another issue to
do this.
- stack
> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
> Key: HBASE-2468
> URL: https://issues.apache.org/jira/browse/HBASE-2468
> Project: HBase
> Issue Type: Improvement
> Components: client
> Reporter: Todd Lipcon
> Assignee: Mingjie Lai
> Fix For: 0.21.0
>
> Attachments: HBASE-2468-trunk.patch
>
>
> A couple different use cases cause storms of reads to META during startup.
> For example, a large MR job will cause each map task to hit meta since it
> starts with an empty cache.
> A couple possible improvements have been proposed:
> - MR jobs could ship a copy of META for the table in the DistributedCache
> - Clients could prewarm cache by doing a large scan of all the meta for the
> table instead of random reads for each miss
> - Each miss could fetch ahead some number of rows in META
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