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From mikewalch <>
Subject [GitHub] accumulo pull request #224: ACCUMULO-4500 ACCUMULO-96 Added summarization
Date Wed, 01 Mar 2017 18:10:10 GMT
Github user mikewalch commented on a diff in the pull request:
    --- Diff: docs/src/main/asciidoc/chapters/summaries.txt ---
    @@ -0,0 +1,209 @@
    +// Licensed to the Apache Software Foundation (ASF) under one or more
    +// contributor license agreements.  See the NOTICE file distributed with
    +// this work for additional information regarding copyright ownership.
    +// The ASF licenses this file to You under the Apache License, Version 2.0
    +// (the "License"); you may not use this file except in compliance with
    +// the License.  You may obtain a copy of the License at
    +// Unless required by applicable law or agreed to in writing, software
    +// distributed under the License is distributed on an "AS IS" BASIS,
    +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    +// See the License for the specific language governing permissions and
    +// limitations under the License.
    +== Summary Statistics
    +=== Overview
    +Accumulo has the ability to generate summary statistics about data in a table
    +using user define functions.  Currently these statistics are only generated for
    +data written to files.  Data recently written to Accumulo that is still in
    +memory will not contribute to summary statistics.
    +This feature can be used to inform a user about what data is in their table.
    +Summary statistics can also be used by compaction strategies to make decisions
    +about which files to compact.  
    +Summary data is stored in each file Accumulo produces.  Accumulo can gather
    +summary information from across a cluster merging it along the way.  In order
    +for this to be fast the, summary information should fit in cache.  There is a
    +dedicated cache for summary data on each tserver with a configurable size.  In
    +order for summary data to fit in cache, it should probably be small.
    +For information on writing a custom summarizer see the javadoc for
    --- End diff --
    Should mention that there are summarizers available for use (and list them) in addition
to creating your own custom serializer

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