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https://issues.apache.org/jira/browse/HBASE-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13205318#comment-13205318
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Phabricator commented on HBASE-5074:
------------------------------------
dhruba has commented on the revision "[jira] [HBASE-5074] Support checksums in
HBase block cache".
INLINE COMMENTS
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java:1545 This is
the initialization code in the constructor that assumes that we always verify
hbase checksums. In the next line, it will be set to false if the minor version
is an old one. Similarly, If there is a HFileSystem and the called has
voluntarily cleared hfs.useHBaseChecksum, then we respect the caller's wishes
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:1 I do not know
of nay performance penalty. For hbase code, this wrapper is traversed only once
when an HFile is opened of an HLog is created. Since the number of times we
open/create a file is miniscule compared to the number of reads/writes to those
files, the overhead (if any) should not show up in any benchmark. I will
validate this on my cluster and report if I see any.
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:1 I do not yet
see a package o.apache.hadoop.hbase.fs Do you want m to create it? There is a
pre-exising class o.a.h.h.utils.FSUtils, that's why I created HFileSystem
inside that package.
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:40 We would
create a method HFileSystem.getLogFs(). The implementation of this method can
open a new filesystem object (for storing transaction logs) Then, HRegionServer
will pass in HFileSystem.getLogFs() into the constructor of HLog().
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:49 Currently, the
only place HFileSystem is created is inside HRegionServer
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:107 You would see
that readfs is the filesystem object that will be used to avoid checksum
verification inside of hdfs.
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java:172 The hadoop
code base recently introduced the method FileSystem.createNonRecursive. But
whoever added it to FileSystem forgot to add it to FilterFileSystem. Apache
hadoop trunk should roll out a patch for this one soon.
REVISION DETAIL
https://reviews.facebook.net/D1521
> support checksums in HBase block cache
> --------------------------------------
>
> Key: HBASE-5074
> URL: https://issues.apache.org/jira/browse/HBASE-5074
> Project: HBase
> Issue Type: Improvement
> Components: regionserver
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: D1521.1.patch, D1521.1.patch, D1521.2.patch,
> D1521.2.patch, D1521.3.patch, D1521.3.patch, D1521.4.patch, D1521.4.patch,
> D1521.5.patch, D1521.5.patch
>
>
> The current implementation of HDFS stores the data in one block file and the
> metadata(checksum) in another block file. This means that every read into the
> HBase block cache actually consumes two disk iops, one to the datafile and
> one to the checksum file. This is a major problem for scaling HBase, because
> HBase is usually bottlenecked on the number of random disk iops that the
> storage-hardware offers.
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