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From "Densel Santhmayor (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-18161) MultiHFileOutputFormat - comprehensive incremental load support
Date Mon, 05 Jun 2017 14:20:04 GMT
Densel Santhmayor created HBASE-18161:

             Summary: MultiHFileOutputFormat - comprehensive incremental load support
                 Key: HBASE-18161
                 URL: https://issues.apache.org/jira/browse/HBASE-18161
             Project: HBase
          Issue Type: New Feature
            Reporter: Densel Santhmayor
            Priority: Minor

h2. Introduction

MapReduce currently supports the ability to write HBase records in bulk to HFiles for a single
table. The file(s) can then be uploaded to the relevant RegionServers information with reasonable
latency. This feature is useful to make a large set of data available for queries at the same
time as well as provides a way to efficiently process very large input into HBase without
affecting query latencies.

There is, however, no support to write variations of the same record key to HFiles belonging
to multiple HBase tables from within the same MapReduce job.  

h2. Goal

The goal of this JIRA is to extend HFileOutputFormat2 to support writing to HFiles for different
tables within the same MapReduce job while single-table HFile features backwards-compatible.

For our use case, we needed to write a record key to a smaller HBase table for quicker access,
and the same record key with a date appended to a larger table for longer term storage with
chronological access. Each of these tables would have different TTL and other settings to
support their respective access patterns. We also needed to be able to bulk write records
to multiple tables with different subsets of very large input as efficiently as possible.
Rather than run the MapReduce job multiple times (one for each table or record structure),
it would be useful to be able to parse the input a single time and write to multiple tables

Additionally, we'd like to maintain backwards compatibility with the existing heavily-used
HFileOutputFormat2 interface to allow benefits such as locality sensitivity (that was introduced
long after we implemented support for multiple tables) to support both single table and multi
table hfile writes. 

h2. Proposal
* Backwards compatibility for existing single table support in HFileOutputFormat2 will be
maintained and in this case, mappers will need to emit the table rowkey as before. However,
a new class - MultiHFileOutputFormat - will provide a helper function to generate a rowkey
for mappers that prefixes the desired tablename to the existing rowkey as well as provides
configureIncrementalLoad support for multiple tables.
* HFileOutputFormat2 will be updated in the following way:
** configureIncrementalLoad will now accept multiple table descriptor and region locator pairs,
analogous to the single pair currently accepted by HFileOutputFormat2. 
** Compression, Block Size, Bloom Type and Datablock settings PER column family that are set
in the Configuration object are now indexed and retrieved by tablename AND column family
** getRegionStartKeys will now support multiple regionlocators and calculate split points
and therefore partitions collectively for all tables. Similarly, now the eventual number of
Reducers will be equal to the total number of partitions across all tables. 
** The RecordWriter class will be able to process rowkeys either with or without the tablename
prepended depending on how configureIncrementalLoad was configured with MultiHFileOutputFormat
or HFileOutputFormat2.
* The use of MultiHFileOutputFormat will write the output into HFiles which will match the
output format of HFileOutputFormat2. However, while the default use case will keep the existing
directory structure with column family name as the directory and HFiles within that directory,
in the case of MultiHFileOutputFormat, it will output HFiles in the output directory with
the following relative paths: 

This aims to be a comprehensive solution to the original tickets - HBASE-3727 and HBASE-16261.
Thanks to [~clayb] for his support.

The patch will be attached shortly.

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