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From afu...@apache.org
Subject svn commit: r1196649 - /incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex
Date Wed, 02 Nov 2011 15:46:59 GMT
Author: afuchs
Date: Wed Nov  2 15:46:58 2011
New Revision: 1196649

URL: http://svn.apache.org/viewvc?rev=1196649&view=rev
Log:
ACCUMULO-111

Modified:
incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex

Modified: incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex
URL: http://svn.apache.org/viewvc/incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex?rev=1196649&r1=1196648&r2=1196649&view=diff
==============================================================================
--- incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex
(original)
+++ incubator/accumulo/branches/1.3/docs/src/user_manual/chapters/table_configuration.tex
Wed Nov  2 15:46:58 2011
@@ -183,7 +183,7 @@ Tables support separate Iterator setting
compaction and upon major compaction. For most uses, tables will have identical
iterator settings for all three to avoid inconsistent results.

-\section{Versioning Iterators and Timestamps}
+\subsection{Versioning Iterators and Timestamps}

Accumulo provides the capability to manage versioned data through the use of
timestamps within the Key. If a timestamp is not specified in the key created by the
@@ -212,7 +212,7 @@ table.iterator.majc.vers.opt.maxVersions
\end{verbatim}
\normalsize

-\subsection{Logical Time}
+\subsubsection{Logical Time}

Accumulo 1.2 introduces the concept of logical time. This ensures that timestamps
set by accumulo always move forward. This helps avoid problems caused by
@@ -228,14 +228,14 @@ user@myinstance> createtable -tl logical
\end{verbatim}
\normalsize

-\subsection{Deletes}
+\subsubsection{Deletes}
Deletes are special keys in accumulo that get sorted along will all the other data.
When a delete key is inserted, accumulo will not show anything that has a
timestamp less than or equal to the delete key. During major compaction, any keys
older than a delete key are omitted from the new file created, and the omitted keys
are removed from disk as part of the regular garbage collection process.

-\section{Filtering Iterators}
+\subsection{Filtering Iterators}
When scanning over a set of key-value pairs it is possible to apply an arbitrary
filtering policy through the use of a FilteringIterator. These types of iterators return
only key-value pairs that satisfy the filter logic. Accumulo has two built-in filtering
@@ -375,3 +375,26 @@ class to Accumulo's lib directory.
An example of an aggregator can be found under\\
accumulo/src/examples/main/java/accumulo/examples/aggregation/SortedSetAggregator.java

+\section{Block Cache}
+
+In order to increase throughput of commonly accessed entries, Accumulo employs a block cache.
+This block cache buffers data in memory so that it doesn't have to be read off of disk.
+The RFile format that Accumulo prefers is a mix of index blocks and data blocks, where the
index blocks are used to find the appropriate data blocks.
+Typical queries to Accumulo result in a binary search over several index blocks followed
by a linear scan of one or more data blocks.
+
+The block cache can be configured on a per-table basis, and all tablets hosted on a tablet
server share a single resource pool.
+To configure the size of the tablet server's block cache, set the following properties:
+\begin{verbatim}
+tserver.cache.data.size: Specifies the size of the cache for file data blocks.
+tserver.cache.index.size: Specifies the size of the cache for file indices.
+\end{verbatim}
+To enable the block cache for your table, set the following properties:
+\begin{verbatim}
+table.cache.block.enable: Determines whether file (data) block cache is enabled.
+table.cache.index.enable: Determines whether index cache is enabled.
+\end{verbatim}
+
+The block cache can have a significant effect on alleviating hot spots, as well as reducing
query latency.
+It is enabled by default for the !METADATA table.
+
+


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