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https://issues.apache.org/jira/browse/HBASE-18161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16058616#comment-16058616
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Densel Santhmayor commented on HBASE-18161:
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I am more than happy to lay the right foundation for future namespace support.
I just didn't think that implementing complete support for namespaces should be
done in this ticket. Since the separator is for internal-use, we should be able
to change it at any time in the future as well. However, to address your
concern, I'd like to understand more.
Did you mean "Using *colon* as separator would make supporting namespace
hard."?
I'm not sure why this would be the case. I was looking at
https://hbase.apache.org/apidocs/src-html/org/apache/hadoop/hbase/TableName.html#line.63
and I saw the line
public final static char NAMESPACE_DELIM = ':';
So this seems to only be a concern if you are looking to use different
separators for namespace separation from tablename vs tablename separation from
rowkey?
I'm not sure why we can't use the same delimiter to separate the namespace from
the tablename as well as the tablename from the rowkey, since when we do
implement namespace support, we can mandate a namespace is necessary when
creating the key, just like we mandate now that the tablename is required when
creating the key for multitable support
Also, namespaces/tablenames according to that source code can only have
letters, digits and '_', so there is no chance of this delimiter ending up in
the namespace (or tablename)
2. I'm more than happy to use a semicolon as separator in the current patch if
you or others think that's the right way to go, just trying to understand
whether there is a technical barrier or not.
> Incremental Load support for Multiple-Table HFileOutputFormat
> -------------------------------------------------------------
>
> Key: HBASE-18161
> URL: https://issues.apache.org/jira/browse/HBASE-18161
> Project: HBase
> Issue Type: New Feature
> Reporter: Densel Santhmayor
> Priority: Minor
> Attachments: MultiHFileOutputFormatSupport_HBASE_18161.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v2.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v3.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v4.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v5.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v6.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v7.patch,
> MultiHFileOutputFormatSupport_HBASE_18161_v8.patch
>
>
> 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 simultaneously.
> 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:
> {noformat}
> --table1
> --family1
> --HFiles
> --table2
> --family1
> --family2
> --HFiles
> {noformat}
> 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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