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From "Densel Santhmayor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18161) Incremental Load support for Multiple-Table HFileOutputFormat
Date Thu, 22 Jun 2017 02:21:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16058616#comment-16058616

Densel Santhmayor commented on HBASE-18161:

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
> 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
> ** 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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