Author: billie
Date: Tue Apr 24 18:48:06 2012
New Revision: 1329932
URL: http://svn.apache.org/viewvc?rev=1329932&view=rev
Log:
added some definitions
Modified:
accumulo/site/trunk/content/glossary.mdtext
Modified: accumulo/site/trunk/content/glossary.mdtext
URL:
http://svn.apache.org/viewvc/accumulo/site/trunk/content/glossary.mdtext?rev=1329932&r1=1329931&r2=1329932&view=diff
==============================================================================
--- accumulo/site/trunk/content/glossary.mdtext (original)
+++ accumulo/site/trunk/content/glossary.mdtext Tue Apr 24 18:48:06 2012
@@ -16,22 +16,28 @@ Notice: Licensed to the Apache Softwa
specific language governing permissions and limitations
under the License.
-- **authorizations** -
-- **column** -
-- **column family** -
-- **column qualifier** -
-- **column visibility** -
-- **key** -
-- **iterator** -
-- **iterator scopes** -
-- **log-structured merge-tree** -
-- **major compaction** -
+- **authorizations** - a set of strings associated with a user or with a
particular scan that will be used to determine which key/value pairs are
visible to the user.
+- **cell** - a set of key/value pairs whose keys differ only in timestamp.
+- **column** - the portion of the key that sorts after the row and is divided
into family, qualifier, and visibility.
+- **column family** - the portion of the key that sorts second and controls
locality groups, the row/column hybrid nature of accumulo.
+- **column qualifier** - the portion of the key that sorts third and provides
additional key uniqueness.
+- **column visibility** - the portion of the key that sorts fourth and
controls user access to individual key/value pairs. Visibilities are boolean
AND (&) and OR (|) combinations of authorization strings with parentheses
required to determine ordering, e.g. (AB&C)|DEF.
+- **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** -
+- **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 visibility.
+- **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
scan.
+- **log-structured merge-tree** - the sorting / flushing / merging scheme on
which BigTable's design is based.
+- **logger** -
+- **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** -
-- **minor compaction** -
-- **permissions** -
-- **row** -
-- **scan** -
-- **tablet** - a contiguous key range; the unit of work for a tablet server
-- **tablet server** -
-- **timestamp** -
-- **value** -
\ No newline at end of file
+- **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** -
+- **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.
+- **tablet** - a contiguous key range; the unit of work for a tablet server.
+- **tablet servers** - a set of servers that hosts reads and writes for
tablets. Each server hosts a distinct set of tablets at any given time, but
the tablets may be hosted by different servers over time.
+- **timestamp** - the portion of the key that controls versioning. Otherwise
identical keys with differing timestamps are considered to be versions of a
single *cell*. Accumulo can be configured to keep the *N* newest versions of
each *cell*. When a deletion entry is inserted, it deletes all earlier
versions for its cell.
+- **value** - immutable bytes associated with a particular key.
\ No newline at end of file
