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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2315) BookKeeper for write-ahead logging
Date Wed, 17 Mar 2010 18:59:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2315?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12846531#action_12846531
] 

Todd Lipcon commented on HBASE-2315:
------------------------------------

Thanks for attaching the design doc, Flavio. Here are a few questions generally about BK (would
be great to address these in the docs too, not just this JIRA):

- Logs are stored replicated on several bookies. If a bookie goes down or loses a disk, the
replication count obviously decreases. Will BK re-replicate the "under-replicated" parts of
the log files? Or do we assume that logs are short-lived enough that we'll never lose all
the replicas during the span of time for which the log is necessary?
- Similar to the above, is there any notion of rack awareness? eg does it ensure that each
part of the log is replicated at least on two racks so that a full rack failure doesn't lose
the logs?

Basically on a broad level what I'm asking is this: HDFS takes a lot of care to ensure availability
of data "forever" across a variety of failure scenarios. From the design doc it wasn't clear
that BK provides the same levels of safety. Can you please clarify what features (if any)
are missing from BK that are present in HDFS with regard to reliability, etc?

> BookKeeper for write-ahead logging
> ----------------------------------
>
>                 Key: HBASE-2315
>                 URL: https://issues.apache.org/jira/browse/HBASE-2315
>             Project: Hadoop HBase
>          Issue Type: New Feature
>          Components: regionserver
>            Reporter: Flavio Paiva Junqueira
>         Attachments: bookkeeperOverview.pdf, HBASE-2315.patch, zookeeper-dev-bookkeeper.jar
>
>
> BookKeeper, a contrib of the ZooKeeper project, is a fault tolerant and high throughput
write-ahead logging service. This issue provides an implementation of write-ahead logging
for hbase using BookKeeper. Apart from expected throughput improvements, BookKeeper also has
stronger durability guarantees compared to the implementation currently used by hbase.

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