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From <>
Subject CMS diff: Apache Accumulo Glossary
Date Tue, 22 Apr 2014 14:09:56 GMT
Clone URL (Committers only):;action=diff;uri=

Index: trunk/content/glossary.mdtext
--- trunk/content/glossary.mdtext	(revision 1589009)
+++ trunk/content/glossary.mdtext	(working copy)
@@ -25,15 +25,15 @@
 - **iterator** - a mechanism for modifying tablet-local portions of the key/value space.
Iterators are used for standard administrative tasks as well as for custom processing.
 - **iterator priority** - an iterator must be configured with a particular scope and priority.
 When a tablet server enters that scope, it will instantiate iterators in priority order starting
from the smallest priority and ending with the largest, and apply each to the data read before
rewriting the data or sending the data to the user.
 - **iterator scopes** - the possible scopes for iterators are where the tablet server is
already reading and/or writing data: minor compaction / flush time (*minc* scope), major compaction
/ file merging time (*majc* scope), and query time (*scan* scope)
-- **gc** - 
+- **gc** - process that identifies temporary files that are no longer needed by any process,
and deletes them.
 - **key** - the key into the distributed sorted map which is accumulo.  The key is subdivided
into row, column, and timestamp.  The column is further divided into  family, qualifier, and
 - **locality group** - a set of column families that will be grouped together on disk.  With
no locality groups configured, data is stored on disk in row order.  If each column family
were configured to be its own locality group, the data for each column would be stored separately,
in row order.  Configuring sets of columns into locality groups is a compromise between the
two approaches and will improve performance when multiple columns are accessed in the same
 - **log-structured merge-tree** - the sorting / flushing / merging scheme on which BigTable's
design is based.
-- **logger** - 
+- **logger** - in 1.4 and older, process that accepts updates to tablet servers and writes
them to local on-disk storage for redundancy. in 1.5 the functionality was subsumed by the
tablet server and datanode with HDFS writes.
 - **major compaction** - merging multiple files into a single file.  If all of a tablet's
files are merged into a single file, it is called a *full major compaction*.
-- **master** - 
+- **master** - process that detects and responds to tablet failures, balances load across
tablet servers by assigning and migrating tablets when required, coordinates table operations,
and handles tablet server logistics (startup, shutdown, recovery).
 - **minor compaction** - flushing data from memory to disk.  Usually this creates a new file
for a tablet, but if the memory flushed is merge-sorted in with data from an existing file
(replacing that file), it is called a *merging minor compaction*.
-- **monitor** -
+- **monitor** - process that displays status and usage information for all Accumulo components.
 - **permissions** - administrative abilities that must be given to a user such as creating
tables or users and changing permissions or configuration parameters.
 - **row** - the portion of the key that is controls atomicity.  Keys with the same row are
guaranteed to remain on a single tablet hosted by a single tablet server, therefore multiple
key/value pairs can be added to or removed from a row at the same time. The row is used for
the primary sorting of the key.
 - **scan** - reading a range of key/value pairs.

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