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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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commit 1b823f519d4e5e1d1b947425c955acd0fd883bc7 1 parent 5b5428f
Keith Turner keith-turner authored
23 docs/src/user_manual/chapters/design.tex
@@ -62,12 +62,6 @@ \subsection{Tablet Server}
62 62 that was previously on a server that failed, reapplying any writes
63 63 found in the write-ahead log to the tablet.
64 64
65   -\subsection{Loggers}
66   -
67   -The Loggers accept updates to Tablet servers and write them to local
68   -on-disk storage. Each tablet server will write their updates to
69   -multiple loggers to preserve data in case of hardware failure.
70   -
71 65 \subsection{Garbage Collector}
72 66
73 67 Accumulo processes will share files stored in HDFS. Periodically, the Garbage
@@ -129,6 +123,23 @@ \section{Compactions}
129 123 remove deleted key-value pairs by omitting key-value pairs suppressed by a
130 124 delete entry when the new file is created.
131 125
  126 +\section{Splitting}
  127 +
  128 +When a table is created it has one tablet. As the table grows its initial
  129 +tablet eventually splits into two tablets. Its likely that one of these
  130 +tablets will migrate to another tablet server. As the table continues to grow,
  131 +its tablets will continue to split and be migrated. The decision to
  132 +automatically split a tablet is based on the size of a tablets files. The
  133 +size threshold at which a tablet splits is configurable per table. In addition
  134 +to automatic splitting, a user can manually add split points to a table to
  135 +create new tablets. Manually splitting a new table can parallelize reads and
  136 +writes giving better initial performance without waiting for automatic
  137 +splitting.
  138 +
  139 +As data is deleted from a table, tablets may shrink. Over time this can lead
  140 +to small or empty tablets. To deal with this, merging of tablets was
  141 +introduced in Accumulo 1.4. This is discussed in more detail later.
  142 +
132 143 \section{Fault-Tolerance}
133 144
134 145 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}
703 703 distcp command. To export a table, it must be offline and stay offline while
704 704 discp runs. The reason it needs to stay offline is to prevent files from being
705 705 deleted. A table can be cloned and the clone taken offline inorder to avoid
706   -losing access to the table. See docs/examples/README.example for an example.
  706 +losing access to the table. See docs/examples/README.export for an example.

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