org.apache.hadoop.hive.ql.io

Interface AcidInputFormat<KEY extends org.apache.hadoop.io.WritableComparable,VALUE>

Type Parameters:

VALUE - The row type

All Superinterfaces:

org.apache.hadoop.mapred.InputFormat<KEY,VALUE>, InputFormatChecker

All Known Implementing Classes:

OrcInputFormat

public interface AcidInputFormat<KEY extends org.apache.hadoop.io.WritableComparable,VALUE>
extends org.apache.hadoop.mapred.InputFormat<KEY,VALUE>, InputFormatChecker

The interface required for input formats that what to support ACID transactions.

The goal is to provide ACID transactions to Hive. There are several primary use cases:

• Streaming ingest- Allow Flume or Storm to stream data into Hive tables with relatively low latency (~30 seconds).
• Dimension table update- Allow updates of dimension tables without overwriting the entire partition (or table) using standard SQL syntax.
• Fact table inserts- Insert data into fact tables at granularity other than entire partitions using standard SQL syntax.
• Fact table update- Update large fact tables to correct data that was previously loaded.

It is important to support batch updates and maintain read consistency within a query. A non-goal is to support many simultaneous updates or to replace online transactions systems.

The design changes the layout of data within a partition from being in files at the top level to having base and delta directories. Each write operation will be assigned a sequential global transaction id and each read operation will request the list of valid transaction ids.

• Old format -

          $partition/$bucket
       

• New format -

          $partition/base_$tid/$bucket
                     delta_$tid_$tid/$bucket
       

With each new write operation a new delta directory is created with events that correspond to inserted, updated, or deleted rows. Each of the files is stored sorted by the original transaction id (ascending), bucket (ascending), row id (ascending), and current transaction id (descending). Thus the files can be merged by advancing through the files in parallel.

The base files include all transactions from the beginning of time (transaction id 0) to the transaction in the directory name. Delta directories include transactions (inclusive) between the two transaction ids.

Because read operations get the list of valid transactions when they start, all reads are performed on that snapshot, regardless of any transactions that are committed afterwards.

The base and the delta directories have the transaction ids so that major (merge all deltas into the base) and minor (merge several deltas together) compactions can happen while readers continue their processing.

To support transitions between non-ACID layouts to ACID layouts, the input formats are expected to support both layouts and detect the correct one.

A note on the KEY of this InputFormat. For row-at-a-time processing, KEY can conveniently pass RowId into the operator pipeline. For vectorized execution the KEY could perhaps represent a range in the batch. Since OrcInputFormat is declared to return NullWritable key, org.apache.hadoop.hive.ql.io.AcidRecordReader is defined to provide access to the RowId. Other implementations of AcidInputFormat can use either mechanism.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	AcidInputFormat.AcidRecordReader<K,V> RecordReader returned by AcidInputFormat working in row-at-a-time mode should AcidRecordReader.
static class	AcidInputFormat.Options Options for controlling the record readers.
static interface	AcidInputFormat.RawReader<V>
static interface	AcidInputFormat.RowReader<V>

Method Summary

Methods

Modifier and Type	Method and Description
AcidInputFormat.RawReader<VALUE>	getRawReader(org.apache.hadoop.conf.Configuration conf, boolean collapseEvents, int bucket, ValidTxnList validTxnList, org.apache.hadoop.fs.Path baseDirectory, org.apache.hadoop.fs.Path[] deltaDirectory) Get a reader that returns the raw ACID events (insert, update, delete).
AcidInputFormat.RowReader<VALUE>	getReader(org.apache.hadoop.mapred.InputSplit split, AcidInputFormat.Options options) Get a record reader that provides the user-facing view of the data after it has been merged together.

Methods inherited from interface org.apache.hadoop.mapred.InputFormat

getRecordReader, getSplits

Methods inherited from interface org.apache.hadoop.hive.ql.io.InputFormatChecker

validateInput

Method Detail

getReader

AcidInputFormat.RowReader<VALUE> getReader(org.apache.hadoop.mapred.InputSplit split,
                                         AcidInputFormat.Options options)
                                           throws IOException

Get a record reader that provides the user-facing view of the data after it has been merged together. The key provides information about the record's identifier (transaction, bucket, record id).

Parameters:

split - the split to read

options - the options to read with

Returns:

a record reader

Throws:

IOException

getRawReader

AcidInputFormat.RawReader<VALUE> getRawReader(org.apache.hadoop.conf.Configuration conf,
                                            boolean collapseEvents,
                                            int bucket,
                                            ValidTxnList validTxnList,
                                            org.apache.hadoop.fs.Path baseDirectory,
                                            org.apache.hadoop.fs.Path[] deltaDirectory)
                                              throws IOException

Get a reader that returns the raw ACID events (insert, update, delete). Should only be used by the compactor.

Parameters:

conf - the configuration

collapseEvents - should the ACID events be collapsed so that only the last version of the row is kept.

bucket - the bucket to read

validTxnList - the list of valid transactions to use

baseDirectory - the base directory to read or the root directory for old style files

deltaDirectory - a list of delta files to include in the merge

Returns:

a record reader

Throws:

IOException