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Subject svn commit: r1196647 - /incubator/accumulo/trunk/docs/src/user_manual/chapters/table_configuration.tex
Date Wed, 02 Nov 2011 15:46:09 GMT
Author: afuchs
Date: Wed Nov  2 15:46:09 2011
New Revision: 1196647



Modified: incubator/accumulo/trunk/docs/src/user_manual/chapters/table_configuration.tex
--- incubator/accumulo/trunk/docs/src/user_manual/chapters/table_configuration.tex (original)
+++ incubator/accumulo/trunk/docs/src/user_manual/chapters/table_configuration.tex Wed Nov
 2 15:46:09 2011
@@ -18,7 +18,7 @@
 Accumulo tables have a few options that can be configured to alter the default
 behavior of Accumulo as well as improve performance based on the data stored.
-These include locality groups, constraints, and iterators.
+These include locality groups, constraints, bloom filters, iterators, and block cache.
 \section{Locality Groups}
 Accumulo supports storing of sets of column families separately on disk to allow
@@ -184,7 +184,7 @@ 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
@@ -213,7 +213,7 @@ table.iterator.majc.vers.opt.maxVersions
-\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
@@ -231,14 +231,14 @@ user@myinstance> createtable -tl logical
 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.
 When scanning over a set of key-value pairs it is possible to apply an arbitrary
 filtering policy through the use of a Filter. Filters are types of iterators that return
 only key-value pairs that satisfy the filter logic. Accumulo has a few built-in filters
@@ -293,7 +293,7 @@ table    | table.iterator.scan.vers.opt.
-\section{Aggregating Iterators}
+\subsection{Aggregating Iterators}
 Accumulo allows aggregating iterators to be configured on tables and column
 families. When an aggregating iterator is set, the iterator is applied across the values
@@ -356,6 +356,29 @@ An example of an aggregator can be found
+\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} Specifies the size of the cache for file data blocks.
+tserver.cache.index.size: Specifies the size of the cache for file indices.
+To enable the block cache for your table, set the following properties:
+table.cache.block.enable: Determines whether file (data) block cache is enabled.
+table.cache.index.enable: Determines whether index cache is enabled.
+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.
 \section{Pre-splitting tables}
 Accumulo will balance and distribute tables accross servers. Before a

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