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https://issues.apache.org/jira/browse/HBASE-18161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16038199#comment-16038199
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Densel Santhmayor commented on HBASE-18161:
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Please correct me if I'm mistaken here.
>From initial analysis, HBASE-3727 did not have the ability to perform
>incremental load and used the tablename as the mapper output key which
>severely limited the throughput for tables with a large number of regions
>since there seems to be only a single reducer per table.
It seems that HBASE-16261 may solve this issue by writing its own partitioner
and while the tablename still needs to be sent as the mapper output key, a
reducer is created for each splitkey partition for all tables. However, a few
things are still not clear to me:
1. The configuration object seems to store only a *single set* of encodings of
compression, block encoding etc per family and this doesn't seem to be done per
table.
2. While HFileOutputFormat2 supports (for now) the KeyValueSortReducer,
PutSortReducer, and TextSortReducer, the new MultiTableHFileOutputFormat class
only seems to support KeyValueSortReducer
My solution relies on upgrading HFileOutputFormat2 to support writing to
multiple tables without changing the underlying behaviour such as locality
sensitivity and partitioning. I updated all encoding functions to use as the
key a combination of tablename and family, and the behaviour of the new class -
MultiHFileOutputFormat - as a public interface as well as providing helper
functions so that Mapper output keys (rowkey) can easily be transformed into a
combination of tablename and rowkey. With only these essential changes, any
further changes to HFileOutputFormat2 will benefit users of
MultiHFileOutputFormat with minor, if any, changes. For example, if we need to
support namespaces before the tablename, it should take only minor changes to a
few overridden functions - perhaps getOutputPath and getTableFamilyCombo
In short, I aim to achieve a comprehensive solution to writing HFiles of
multiple tables in a single MR job, while preserving existing logic in
HFileOutputFormat2 with minimal code changes, effective client helper functions
and meticulous error checking (If 3 tables are configured initially through
configureIncrementalLoad, then mapper output MUST only include either of the 3
tables or an error is thrown when writing)
> 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 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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