hive SerDe序列化和反序列序列化表

1 什么是SerDe

SerDe 是两个单词的拼写 serialized(序列化) 和 deserialized(反序列化)。 什么是序列化和反序列化呢？

当进程在进行远程通信时，彼此可以发送各种类型的数据，无论是什么类型的数据都会以 二进制序列的形式在网络上传送。发送方需要把对象转化为字节序列才可在网络上传输， 称为对象序列化；接收方则需要把字节序列恢复为对象，称为对象的反序列化。

Hive的反序列化是对key/value反序列化成hive table的每个列的值。Hive可以方便 的将数据加载到表中而不需要对数据进行转换，这样在处理海量数据时可以节省大量的时间。

Hive SerDe

What is a SerDe?

• SerDe is a short name for "Serializer and Deserializer."
• Hive uses SerDe (and FileFormat) to read and write table rows.
• HDFS files --> InputFileFormat --> <key, value> --> Deserializer --> Row object     （读流程）
• Row object --> Serializer --> <key, value> --> OutputFileFormat --> HDFS files      （写流程）

----参考官网：https://cwiki.apache.org/confluence/display/Hive/DeveloperGuide#DeveloperGuide-HiveSerDe

2 Built-in SerDes（SerDe包括内置类型）

• Avro (Hive 0.9.1 and later)
• ORC (Hive 0.11 and later)
• RegEx
• Thrift
• Parquet (Hive 0.13 and later)
• CSV (Hive 0.14 and later)
• JsonSerDe (Hive 0.12 and later in hcatalog-core)

----参考官网：https://cwiki.apache.org/confluence/display/Hive/SerDe

3 序列化的使用

3.1 建表时指定序列化方式

· RegexSerDe

CREATE TABLE apachelog (
  host STRING,
  identity STRING,
  user STRING,
  time STRING,
  request STRING,
  status STRING,
  size STRING,
  referer STRING,
  agent STRING)
ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.RegexSerDe'
WITH SERDEPROPERTIES (
  "input.regex" = "([^]*) ([^]*) ([^]*) (-|\[^\]*\]) ([^ "]*|"[^"]*") (-|[0-9]*) (-|[0-9]*)(?: ([^ "]*|".*") ([^ "]*|".*"))?"
)
STORED AS TEXTFILE;

· JsonSerDe

ADD JAR /usr/lib/hive-hcatalog/lib/hive-hcatalog-core.jar;

CREATE TABLE my_table(a string, b bigint, ...)
ROW FORMAT SERDE 'org.apache.hive.hcatalog.data.JsonSerDe'
STORED AS TEXTFILE;

· CSVSerDe

CREATE TABLE my_table(a string, b string) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde' WITH SERDEPROPERTIES ("separatorChar" = "	","quoteChar"= "'","escapeChar"= "\")   STORED AS TEXTFILE;

·ORCSerDe

ROW FORMAT SERDE
  'org.apache.hadoop.hive.ql.io.orc.OrcSerde'
  STORED AS INPUTFORMAT
  'org.apache.hadoop.hive.ql.io.orc.OrcInputFormat'
  OUTPUTFORMAT
  'org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat'

参考官网：

Registration of Native SerDes

As of Hive 0.14 a registration mechanism has been introduced for native Hive SerDes.  This allows dynamic binding between a "STORED AS" keyword in place of a triplet of {SerDe, InputFormat, and OutputFormat} specification, in CreateTable statements.

The following mappings have been added through this registration mechanism:

Syntax	Equivalent
Syntax	Equivalent
STORED AS AVRO / STORED AS AVROFILE	ROW FORMAT SERDE   'org.apache.hadoop.hive.serde2.avro.AvroSerDe'   STORED AS INPUTFORMAT   'org.apache.hadoop.hive.ql.io.avro.AvroContainerInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.hive.ql.io.avro.AvroContainerOutputFormat'
STORED AS ORC / STORED AS ORCFILE	ROW FORMAT SERDE   'org.apache.hadoop.hive.ql.io.orc.OrcSerde'   STORED AS INPUTFORMAT   'org.apache.hadoop.hive.ql.io.orc.OrcInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat'
STORED AS PARQUET / STORED AS PARQUETFILE	ROW FORMAT SERDE   'org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe'   STORED AS INPUTFORMAT   'org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat'
STORED AS RCFILE	STORED AS INPUTFORMAT   'org.apache.hadoop.hive.ql.io.RCFileInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.hive.ql.io.RCFileOutputFormat'
STORED AS SEQUENCEFILE	STORED AS INPUTFORMAT   'org.apache.hadoop.mapred.SequenceFileInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.mapred.SequenceFileOutputFormat'
STORED AS TEXTFILE	STORED AS INPUTFORMAT   'org.apache.hadoop.mapred.TextInputFormat'   OUTPUTFORMAT   'org.apache.hadoop.hive.ql.io.IgnoreKeyTextOutputFormat'