The document discusses ORC (Optimized Row Columnar) file format, highlighting its advantages over previous formats used in Hadoop applications, such as improved performance, self-describing structure, and support for schema evolution. It details the file and stripe structure, optimization techniques, and the integration of ORC with Hive and other tools. Additionally, it emphasizes current features like column encryption and the ability to handle ACID transactions for better data management.

1. ORC File –
Optimizing Your Big Data
Owen O’Malley, Co-founder Hortonworks
Apache Hadoop, Hive, ORC, and
Incubator
@owen_omalley

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Overview

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In the Beginning…
 Hadoop applications used text or SequenceFile
– Text is slow and not splittable when compressed
– SequenceFile only supports key and value and user-defined serialization
 Hive added RCFile
– User controls the columns to read and decompress
– No type information and user-defined serialization
– Finding splits was expensive
 Avro files created
– Type information included!
– Had to read and decompress entire row

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ORC File Basics
 Columnar format
– Enables user to read & decompress just the bytes they need
 Fast
– See https://www.slideshare.net/HadoopSummit/file-format-benchmark-avro-json-orc-parquet
 Indexed
 Self-describing
– Includes all of the information about types and encoding
 Rich type system
– All of Hive’s types including timestamp, struct, map, list, and union

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File Compatibility
 Backwards compatibility
– Automatically detect the version of the file and read it.
 Forward compatibility
– Most changes are made so old readers will read the new files
– Maintain the ability to write old files via orc.write.format
– Always write old version until your last cluster upgrades
 Current file versions
– 0.11 – Original version
– 0.12 – Updated run length encoding (RLE)

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File Structure
 File contains a list of stripes, which are sets of rows
– Default size is 64MB
– Large stripe size enables efficient reads
 Footer
– Contains the list of stripe locations
– Type description
– File and stripe statistics
 Postscript
– Compression parameters
– File format version

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Stripe Structure
 Indexes
– Offsets to jump to start of row group
– Row group size defaults to 10,000 rows
– Minimum, Maximum, and Count of each column
 Data
– Data for the stripe organized by column
 Footer
– List of stream locations
– Column encoding information

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File Layout
Page 8
Column 1
Column 2
Column 7
Column 8
Column 3
Column 6
Column 4
Column 5
Column 1
Column 2
Column 7
Column 8
Column 3
Column 6
Column 4
Column 5
Index Data
Row Data
Stripe Footer
~64MBStripe
Index Data
Row Data
Stripe Footer
~64MBStripe
Index Data
Row Data
Stripe Footer
~64MBStripe
File Footer
Postscript
File Metadata

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Schema Evolution
 ORC now supports schema evolution
– Hive 2.1 – append columns or type conversion
– Upcoming Hive 2.3 – map columns or inner structures by name
– User passes desired schema to ORC reader
 Type conversions
– Most types will convert although some are ugly.
– If the value doesn’t fit in the new type, it will become null.
 Cautions
– Name mapping requires ORC files written by Hive ≥ 2.0
– Some of the type conversions are slow

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Using ORC

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From Hive or Presto
 Modify your table definition:
– create table my_table (
name string,
address string,
) stored as orc;
 Import data:
– insert overwrite table my_table select * from my_staging;
 Use either configuration or table properties
– tblproperties ("orc.compress"="NONE")
– set hive.exec.orc.default.compress=NONE;

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From Java
 Use the ORC project rather than Hive’s ORC.
– Hive’s master branch uses it.
– Maven group id: org.apache.orc version: 1.4.0
– nohive classifier avoids interfering with Hive’s packages
 Two levels of access
– orc-core – Faster access, but uses Hive’s vectorized API
– orc-mapreduce – Row by row access, simpler OrcStruct API
 MapReduce API implements WritableComparable
– Can be shuffled
– Need to specify type information in configuration for shuffle or output

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From C++
 Pure C++ client library
– No JNI or JDK so client can estimate and control memory
 Combine with pure C++ HDFS client from HDFS-8707
– Work ongoing in feature branch, but should be committed soon.
 Reader is stable and in production use.
 Alibaba has created a writer and is contributing it to Apache ORC.
– Should be in the next release ORC 1.5.0.

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Command Line
 Using hive –orcfiledump from Hive
– -j -p – pretty prints the metadata as JSON
– -d – prints data as JSON
 Using java -jar orc-tools-1.4.0-uber.jar from ORC
– meta – print the metadata as JSON
– data – print data as JSON
– convert – convert JSON to ORC
– json-schema – scan a set of JSON documents to find the matching schema

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Optimization

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Stripe Size
 Makes a huge difference in performance
– orc.stripe.size or hive.exec.orc.default.stripe.size
– Controls the amount of buffer in writer. Default is 64MB
– Trade off
• Large stripes = Large more efficient reads
• Small stripes = Less memory and more granular processing splits
 Multiple files written at the same time will shrink stripes
– Use Hive’s hive.optimize.sort.dynamic.partition
– Sorting dynamic partitions means a one writer at a time

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HDFS Block Padding
 The stripes don’t align exactly with HDFS blocks
 HDFS scatters blocks around cluster
 Often want to pad to block boundaries
– Costs space, but improves performance
– hive.exec.orc.default.block.padding – true
– hive.exec.orc.block.padding.tolerance – 0.05
Index Data
Row Data
Stripe Footer
~64MBStripe
Index Data
Row Data
Stripe Footer
~64MBStripe
Index Data
Row Data
Stripe Footer
~64MBStripe
HDFS Block
HDFS Block
Padding
File Footer
Postscript
File Metadata

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Predicate Push Down
 Reader is given a SearchArg
– Limited set predicates over column and literal value
– Reader will skip over any parts of file that can’t contain valid rows
 ORC indexes at three levels:
– File
– Stripe
– Row Group (10k rows)
 Reader still needs to apply predicate to filter out single rows

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Row Pruning
 Every primitive column has minimum and maximum at each level
– Sorting your data within a file helps a lot
– Consider sorting instead of making lots of partitions
 Writer can optionally include bloomfilters
– Provides a probabilistic bitmap of hashcodes
– Only works with equality predicates at the row group level
– Requires significant space in the file
– Manually enabled by using orc.bloom.filter.columns
– Use orc.bloom.filter.fpp to set the false positive rate (default 0.05)
– Set the default charset in JVM via -Dfile.encoding=UTF-8

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Row Pruning Example
 TPC-DS
– from tpch1000.lineitem where l_orderkey = 1212000001;
 Rows Read
– Nothing – 5,999,989,709
– Min/Max – 540,000
– BloomFilter – 10,000
 Time Taken
– Nothing – 74 sec
– Min/Max – 4.5 sec
– BloomFilter – 1.3 sec

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Split Calculation
 Hive’s OrcInputFormat has three strategies for split calculation
– BI
• Small fast queries
• Splits based on HDFS blocks
– ETL
• Large queries
• Read file footer and apply SearchArg to stripes
• Can include footer in splits (hive.orc.splits.include.file.footer)
– Hybrid
• If small files or lots of files, use BI

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LLAP – Live Long & Process
 Provides a persistent service to speed up Hive
– Caches ORC and text data
– Saves costs of Yarn container & JVM spin up
– JIT finishes after first few seconds
 Cache uses ORC’s RLE
– Decompresses zlib or Snappy
– RLE is fast and saves memory
– Automatically caches hot columns and partitions
 Allows Spark to use Hive’s column and row security

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Current Work In Progress

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Speed Improvements for ACID
 Hive supports ACID transactions on ORC tables
– Uses delta files in HDFS to store changes to each partition
– Delta files store insert/update/delete operations
– Used to support SQL insert commands
 Unfortunately, update operations don’t allow predicate push down
on the deltas
 In the upcoming Hive 2.3, we added a new ACID layout
– It change updates to an insert and delete
– Allows predicate pushdown even on the delta files
 Also added SQL merge command in Hive 2.2

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Column Encryption (ORC-14)
 Allows users to encrypt some of the columns of the file
– Provides column level security even with access to raw files
– Uses Key Management Server from Ranger or Hadoop
– Includes both the data and the index
– Daily key rolling can anonymize data after 90 days
 User specifies how data is masked if user doesn’t have access
– Nullify
– Redact
– SHA256

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Thank You
@owen_omalley
owen@hortonworks.com