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ACCUMULO-896 Added some info about automatic splitting to user manual.

git-svn-id: 13f79535-47bb-0310-9956-ffa450edef68
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1 parent 5b5428f commit 1b823f519d4e5e1d1b947425c955acd0fd883bc7 @keith-turner keith-turner committed Mar 20, 2013
Showing with 18 additions and 7 deletions.
  1. +17 −6 docs/src/user_manual/chapters/design.tex
  2. +1 −1 docs/src/user_manual/chapters/table_configuration.tex
23 docs/src/user_manual/chapters/design.tex
@@ -62,12 +62,6 @@ \subsection{Tablet Server}
that was previously on a server that failed, reapplying any writes
found in the write-ahead log to the tablet.
-The Loggers accept updates to Tablet servers and write them to local
-on-disk storage. Each tablet server will write their updates to
-multiple loggers to preserve data in case of hardware failure.
\subsection{Garbage Collector}
Accumulo processes will share files stored in HDFS. Periodically, the Garbage
@@ -129,6 +123,23 @@ \section{Compactions}
remove deleted key-value pairs by omitting key-value pairs suppressed by a
delete entry when the new file is created.
+When a table is created it has one tablet. As the table grows its initial
+tablet eventually splits into two tablets. Its likely that one of these
+tablets will migrate to another tablet server. As the table continues to grow,
+its tablets will continue to split and be migrated. The decision to
+automatically split a tablet is based on the size of a tablets files. The
+size threshold at which a tablet splits is configurable per table. In addition
+to automatic splitting, a user can manually add split points to a table to
+create new tablets. Manually splitting a new table can parallelize reads and
+writes giving better initial performance without waiting for automatic
+As data is deleted from a table, tablets may shrink. Over time this can lead
+to small or empty tablets. To deal with this, merging of tablets was
+introduced in Accumulo 1.4. This is discussed in more detail later.
If a TabletServer fails, the Master detects it and automatically reassigns the tablets
2 docs/src/user_manual/chapters/table_configuration.tex
@@ -703,4 +703,4 @@ \section{Exporting Tables}
distcp command. To export a table, it must be offline and stay offline while
discp runs. The reason it needs to stay offline is to prevent files from being
deleted. A table can be cloned and the clone taken offline inorder to avoid
-losing access to the table. See docs/examples/README.example for an example.
+losing access to the table. See docs/examples/README.export for an example.

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