Hive: parsing JSON

Question

I am trying to get some values out of nested JSON for millions of rows (5 TB+ table). What is the most efficient way to do this?

Here is an example:

{"country":"US","page":227,"data":{"ad":{"impressions":{"s":10,"o":10}}}}

I need these values out of the above JSON:

Country        Page      impressions_s       impressions_o
---------      -----     -------------       --------------
US              2        10                  10

This is Hive's json_tuple function, I am not sure if this is the best function. https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-getjsonobject

Answer 1

You can use get_json_object:

 select get_json_object(fieldname, '$.country'), 
        get_json_object(fieldname, '$.data.ad.s') from ... 

You will get better performance with json_tuple but I found a "how to" to get the values in json inside json; To formating your table you can use something like this:

from table t lateral view explode( split(regexp_replace(get_json_object(ln, ''$.data.ad.s'), '\\[|\\]', ''), ',' ) ) tb1 as s this code above will transform you "Array" in a column.

form more: https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF

I hope this help ...

Answer 2

Here is what you can quickly try , I would suggest to use Json-Ser-De.

nano /tmp/hive-parsing-json.json

{"country":"US","page":227,"data":{"ad":{"impressions":{"s":10,"o":10}}}}

Create base table :

hive > CREATE TABLE hive_parsing_json_table ( json string );

Load json file to Table :

hive > LOAD DATA LOCAL INPATH  '/tmp/hive-parsing-json.json' INTO TABLE hive_parsing_json_table;

Query the table :

hive >  select v1.Country, v1.Page, v4.impressions_s, v4.impressions_o 
from hive_parsing_json_table hpjp
     LATERAL VIEW json_tuple(hpjp.json, 'country', 'page', 'data') v1
     as Country, Page, data
     LATERAL VIEW json_tuple(v1.data, 'ad') v2
     as Ad
     LATERAL VIEW json_tuple(v2.Ad, 'impressions') v3
     as Impressions
     LATERAL VIEW json_tuple(v3.Impressions, 's' , 'o') v4
     as impressions_s,impressions_o;  

Output :

v1.country  v1.page     v4.impressions_s    v4.impressions_o
US      227     10          10

Answer 3

Using hive native json-serde('org.apache.hive.hcatalog.data.JsonSerDe') you can do this.. here are the steps

ADD JAR /path/to/hive-hcatalog-core.jar;

create a table as below 
 CREATE TABLE json_serde_nestedjson (
  country string,
  page int,
  data struct < ad: struct < impressions: struct < s:int, o:int  > > >
)
ROW FORMAT SERDE 'org.apache.hive.hcatalog.data.JsonSerDe';

then load data(stored in file)

LOAD DATA LOCAL INPATH '/tmp/nested.json' INTO TABLE json_serde_nestedjson;

then get required data using

SELECT country, page, data.ad.impressions.s, data.ad.impressions.o 
FROM json_serde_nestedjson;  

Answer 4

Implementing a SerDe to parse your data in JSON is a better way for your case.

A tutorial on how to implement SerDe for parsing JSON can be found here

http://blog.cloudera.com/blog/2012/12/how-to-use-a-serde-in-apache-hive/

You can use the following sample SerDe implementation as well

https://github.com/rcongiu/Hive-JSON-Serde