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From dm...@apache.org
Subject svn commit: r1342094 - in /hbase/trunk/src/docbkx: book.xml ops_mgt.xml
Date Wed, 23 May 2012 23:41:02 GMT
Author: dmeil
Date: Wed May 23 23:41:02 2012
New Revision: 1342094

URL: http://svn.apache.org/viewvc?rev=1342094&view=rev
Log:
hbase-6082.  porting hbck document to the RefGuide Appendix

Modified:
    hbase/trunk/src/docbkx/book.xml
    hbase/trunk/src/docbkx/ops_mgt.xml

Modified: hbase/trunk/src/docbkx/book.xml
URL: http://svn.apache.org/viewvc/hbase/trunk/src/docbkx/book.xml?rev=1342094&r1=1342093&r2=1342094&view=diff
==============================================================================
--- hbase/trunk/src/docbkx/book.xml (original)
+++ hbase/trunk/src/docbkx/book.xml Wed May 23 23:41:02 2012
@@ -2711,6 +2711,195 @@ myHtd.setValue(HTableDescriptor.SPLIT_PO
     </qandaset>
   </appendix>
 
+  <appendix xml:id="hbck.in.depth">
+    <title>hbck In Depth</title>
+	<para>HBaseFsck (hbck) is a tool for checking for region consistency and table integrity
problems
+and repairing a corrupted HBase. It works in two basic modes -- a read-only inconsistency
+identifying mode and a multi-phase read-write repair mode.
+	</para>
+	<section>
+	  <title>Running hbck to identify inconsistencies</title>
+To check to see if your HBase cluster has corruptions, run hbck against your HBase cluster:
+<programlisting>
+$ ./bin/hbase hbck
+</programlisting>
+	<para>
+At the end of the commands output it prints OK or tells you the number of INCONSISTENCIES
+present. You may also want to run run hbck a few times because some inconsistencies can be
+transient (e.g. cluster is starting up or a region is splitting). Operationally you may want
to run
+hbck regularly and setup alert (e.g. via nagios) if it repeatedly reports inconsistencies
.
+A run of hbck will report a list of inconsistencies along with a brief description of the
regions and
+tables affected. The using the <code>-details</code> option will report more
details including a representative
+listing of all the splits present in all the tables.	
+	</para>
+<programlisting>
+$ ./bin/hbase hbck -details
+</programlisting>
+	</section>
+	<section><title>Inconsistencies</title>
+	<para>
+	If after several runs, inconsistencies continue to be reported, you may have encountered
a
+corruption. These should be rare, but in the event they occur newer versions of HBase include
+the hbck tool enabled with automatic repair options.
+	</para>
+	<para>
+	There are two invariants that when violated create inconsistencies in HBase:
+	</para>
+	<itemizedlist>
+	  <listitem>HBase’s region consistency invariant is satisfied if every region
is assigned and
+deployed on exactly one region server, and all places where this state kept is in
+accordance.
+	</listitem>
+	<listitem>HBase’s table integrity invariant is satisfied if for each table, every
possible row key
+resolves to exactly one region.
+	</listitem>
+	</itemizedlist>
+	<para>
+Repairs generally work in three phases -- a read-only information gathering phase that identifies
+inconsistencies, a table integrity repair phase that restores the table integrity invariant,
and then
+finally a region consistency repair phase that restores the region consistency invariant.
+Starting from version 0.90.0, hbck could detect region consistency problems report on a subset
+of possible table integrity problems. It also included the ability to automatically fix the
most
+common inconsistency, region assignment and deployment consistency problems. This repair
+could be done by using the <code>-fix</code> command line option. These problems
close regions if they are
+open on the wrong server or on multiple region servers and also assigns regions to region
+servers if they are not open.
+</para>
+<para>
+Starting from HBase versions 0.90.7, 0.92.2 and 0.94.0, several new command line options
are
+introduced to aid repairing a corrupted HBase. This hbck sometimes goes by the nickname
+“uberhbck”. Each particular version of uber hbck is compatible with the HBase’s
of the same
+major version (0.90.7 uberhbck can repair a 0.90.4). However, versions &lt;=0.90.6 and
versions
+&lt;=0.92.1 may require restarting the master or failing over to a backup master.
+</para>
+	</section>
+	<section><title>Localized repairs</title>
+	<para>
+	When repairing a corrupted HBase, it is best to repair the lowest risk inconsistencies first.
+These are generally region consistency repairs -- localized single region repairs, that only
modify
+in-memory data, ephemeral zookeeper data, or patch holes in the META table.
+Region consistency requires that the HBase instance has the state of the region’s data
in HDFS
+(.regioninfo files), the region’s row in the .META. table., and region’s deployment/assignments
on
+region servers and the master in accordance. Options for repairing region consistency include:
+	<itemizedlist>
+		<listitem><code>-fixAssignments</code> (equivalent to the 0.90 <code>-fix</code>
option) repairs unassigned, incorrectly
+assigned or multiply assigned regions.
+		</listitem>
+		<listitem><code>-fixMeta</code> which removes meta rows when corresponding
regions are not present in
+HDFS and adds new meta rows if they regions are present in HDFS while not in META.
+		</listitem>
+	</itemizedlist>
+	To fix deployment and assignment problems you can run this command:
+</para>
+<programlisting>
+$ ./bin/hbase hbck -fixAssignments
+</programlisting>
+To fix deployment and assignment problems as well as repairing incorrect meta rows you can
+run this command:.
+<programlisting>
+$ ./bin/hbase hbck -fixAssignments -fixMeta
+</programlisting>
+There are a few classes of table integrity problems that are low risk repairs. The first
two are
+degenerate (startkey == endkey) regions and backwards regions (startkey > endkey). These
are
+automatically handled by sidelining the data to a temporary directory (/hbck/xxxx).
+The third low-risk class is hdfs region holes. This can be repaired by using the:
+	<itemizedlist>
+		<listitem><code>-fixHdfsHoles</code> option for fabricating new empty
regions on the file system.
+If holes are detected you can use -fixHdfsHoles and should include -fixMeta and -fixAssignments
to make the new region consistent.
+		</listitem>
+	</itemizedlist>
+<programlisting>
+$ ./bin/hbase hbck -fixAssignments -fixMeta -fixHdfsHoles
+</programlisting>
+Since this is a common operation, we’ve added a the <code>-repairHoles</code>
flag that is equivalent to the
+previous command:
+<programlisting>
+$ ./bin/hbase hbck -repairHoles
+</programlisting>
+If inconsistencies still remain after these steps, you most likely have table integrity problems
+related to orphaned or overlapping regions.
+	</section>
+	<section><title>Region Overlap Repairs</title>
+Table integrity problems can require repairs that deal with overlaps. This is a riskier operation
+because it requires modifications to the file system, requires some decision making, and
may
+require some manual steps. For these repairs it is best to analyze the output of a <code>hbck
-details</code>
+run so that you isolate repairs attempts only upon problems the checks identify. Because
this is
+riskier, there are safeguard that should be used to limit the scope of the repairs.
+WARNING: This is a relatively new and have only been tested on online but idle HBase instances
+(no reads/writes). Use at your own risk in an active production environment!
+The options for repairing table integrity violations include:
+	<itemizedlist>
+		<listitem><code>-fixHdfsOrphans</code> option for “adopting”
a region directory that is missing a region
+metadata file (the .regioninfo file).
+		</listitem>
+		<listitem><code>-fixHdfsOverlaps</code> ability for fixing overlapping
regions
+		</listitem>
+	</itemizedlist>
+When repairing overlapping regions, a region’s data can be modified on the file system
in two
+ways: 1) by merging regions into a larger region or 2) by sidelining regions by moving data
to
+“sideline” directory where data could be restored later. Merging a large number
of regions is
+technically correct but could result in an extremely large region that requires series of
costly
+compactions and splitting operations. In these cases, it is probably better to sideline the
regions
+that overlap with the most other regions (likely the largest ranges) so that merges can happen
on
+a more reasonable scale. Since these sidelined regions are already laid out in HBase’s
native
+directory and HFile format, they can be restored by using HBase’s bulk load mechanism.
+The default safeguard thresholds are conservative. These options let you override the default
+thresholds and to enable the large region sidelining feature.
+	<itemizedlist>
+		<listitem><code>-maxMerge &lt;n&gt;</code> maximum number of
overlapping regions to merge
+		</listitem>
+		<listitem><code>-sidelineBigOverlaps</code> if more than maxMerge regions
are overlapping, sideline attempt
+to sideline the regions overlapping with the most other regions.
+		</listitem>
+		<listitem><code>-maxOverlapsToSideline &lt;n&gt;</code> if sidelining
large overlapping regions, sideline at most n
+regions.
+		</listitem>
+	</itemizedlist>
+		
+Since often times you would just want to get the tables repaired, you can use this option
to turn
+on all repair options:
+	<itemizedlist>
+		<listitem><code>-repair</code> includes all the region consistency options
and only the hole repairing table
+integrity options.
+		</listitem>
+	</itemizedlist>
+Finally, there are safeguards to limit repairs to only specific tables. For example the following
+command would only attempt to repair table TableFoo and TableBar.
+<programlisting>
+$ ./bin/hbase/ hbck -repair TableFoo TableBar
+</programlisting>
+	<section><title>Special cases: Meta is not properly assigned</title>
+There are a few special cases that hbck can handle as well.
+Sometimes the meta table’s only region is inconsistently assigned or deployed. In this
case
+there is a special <code>-fixMetaOnly</code> option that can try to fix meta
assignments.
+<programlisting>
+$ ./bin/hbase hbck -fixMetaOnly -fixAssignments
+</programlisting>
+	</section>
+	<section><title>Special cases: HBase version file is missing</title>
+HBase’s data on the file system requires a version file in order to start. If this flie
is missing, you
+can use the <code>-fixVersionFile</code> option to fabricating a new HBase version
file. This assumes that
+the version of hbck you are running is the appropriate version for the HBase cluster.	
+	</section>
+	<section><title>Special case: Root and META are corrupt.</title>
+The most drastic corruption scenario is the case where the ROOT or META is corrupted and
+HBase will not start. In this case you can use the OfflineMetaRepair tool create new ROOT
+and META regions and tables.
+This tool assumes that HBase is offline. It then marches through the existing HBase home
+directory, loads as much information from region metadata files (.regioninfo files) as possible
+from the file system. If the region metadata has proper table integrity, it sidelines the
original root
+and meta table directories, and builds new ones with pointers to the region directories and
their
+data.
+<programlisting>
+$ ./bin/hbase org.apache.hadoop.hbase.util.OfflineMetaRepair
+</programlisting>
+NOTE: This tool is not as clever as uberhbck but can be used to bootstrap repairs that uberhbck
+can complete.
+If the tool succeeds you should be able to start hbase and run online repairs if necessary.
+	</section>
+	</section>
+  </appendix>
+
   <appendix xml:id="compression">
 
     <title >Compression In HBase<indexterm><primary>Compression</primary></indexterm></title>

Modified: hbase/trunk/src/docbkx/ops_mgt.xml
URL: http://svn.apache.org/viewvc/hbase/trunk/src/docbkx/ops_mgt.xml?rev=1342094&r1=1342093&r2=1342094&view=diff
==============================================================================
--- hbase/trunk/src/docbkx/ops_mgt.xml (original)
+++ hbase/trunk/src/docbkx/ops_mgt.xml Wed May 23 23:41:02 2012
@@ -69,6 +69,8 @@ Valid program names are:
         Passing <command>-fix</command> may correct the inconsistency (This latter
         is an experimental feature).
         </para>
+        <para>For more information, see <xref linkend="hbck.in.depth"/>.
+        </para>
     </section>
     <section xml:id="hfile_tool2"><title>HFile Tool</title>
         <para>See <xref linkend="hfile_tool" />.</para>



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