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https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12876428#action_12876428
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HBase Review Board commented on HBASE-2468:
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Message from: st...@duboce.net
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Ship it!
I think this good to go. Seem my comments below. See what you think. My one
concern is the number of calls to getRowOrBefore... hopefully this patch cuts
down overall on our need to use this function. I'd like to hear your opinion
on that.
src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/98/#comment744>
This is code duplicated from elsewhere. Can I help make it so we don't
have to do this duplication? Or, for now, since this your fist patch, we can
put it off IF you file a JIRA to fix the duplication (smile).
src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/98/#comment745>
So we start scanning at 'row'? Is this the 'row' the user asked for? No,
it needs to be the row in the .META. table, right? We need to find the row in
.META. that contains the asked for row first? NM, I see below how the row here
is made.. .this looks right.
src/main/java/org/apache/hadoop/hbase/client/HTable.java
<http://review.hbase.org/r/98/#comment746>
This is a nice little facility.
src/main/java/org/apache/hadoop/hbase/client/MetaScanner.java
<http://review.hbase.org/r/98/#comment747>
OK. This looks right.
src/main/java/org/apache/hadoop/hbase/client/MetaScanner.java
<http://review.hbase.org/r/98/#comment748>
getRowOrBefore is an expensive call. Are we sure we are not calling this
too often?
- 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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