Structure Difference between partitioning and bucketing in hive

Question

I created two tables:

1) One for Partitioning with bucketing
2) Only bucketing table

I know the concepts of partitioning and bucketing in hive. But I am little bit confused because I have read that 'partition creates directory and bucketing creates files'. I agree with the first part because I can see that in HDFS Hive Warehouse but I am not able to see any files for the ONLY bucketing table in HDFS except the data file which I loaded into the table. So where are the files of ONLY bucketing table ? The files which I am able to see under partitioned directory is it that one like for eg: 00000_0but this one can be for the partitioned table but what about the other bucketed table ??
Below is my code for creating table:

CREATE TABLE Employee(
ID BIGINT,
NAME STRING, 
SALARY BIGINT,
COUNTRY STRING 
)
CLUSTERED BY(ID) INTO 5 BUCKETS
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE;

Code for load data is as below :

load data local inpath '/home/cloudera/Desktop/SampleData.txt' into table employee;

I have read that buckets are created when we create table.Please correct me if I am missing something or going wrong.Anyone help please ?

Marco99 Marco99 · Accepted Answer · 2017-10-19T05:56:39

I created hive external tables (which is usually my choice). You can stick on to yours.

Please follow these steps:

Create a database

CREATE DATABASE IF NOT EXISTS testdb LOCATION '/hivedb/testdb';

Create a clustered table (bucketed table)

CREATE TABLE testdb.Employee(
ID BIGINT,
NAME STRING, 
SALARY BIGINT,
COUNTRY STRING 
)
CLUSTERED BY(ID) INTO 5 BUCKETS
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE
LOCATION '/hivedb/testdb/employee';

Create a plain table

CREATE TABLE testdb.Employee_plain_table(
ID BIGINT,
NAME STRING, 
SALARY BIGINT,
COUNTRY STRING 
)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE
LOCATION '/hivedb/testdb/employee_plain_table';

Enforce bucketing, as recommended by @lake in the previous answer
```
set hive.enforce.bucketing = true;
```

Create a data file ('data.txt'). I created a data file with 20 records.

1,AAAAA,1000.00,USA
2,BBBBB,2000.00,CANADA
3,CCCCC,3000.00,MEXICO
4,DDDDD,4000.00,BRAZIL
5,EEEEE,5000.00,ARGENTINA
6,DDDDD,6000.00,CHILE
7,FFFFF,7000.00,BOLIVIA
8,GGGGG,8000.00,VENEZUELA
9,HHHHH,9000.00,PERU
10,IIIII,10000.00,COLOMBIA
11,JJJJJ,11000.00,EQUADOR
12,KKKKK,12000.00,URUGUAY
13,LLLLL,13000.00,PARAGUAY
14,MMMMM,14000.00,GUYANA
15,NNNNN,15000.00,NICARAGUA
16,OOOOO,16000.00,PANAMA
17,PPPPP,17000.00,COSTA RICA
18,QQQQQ,18000.00,HAITI
19,RRRRR,19000.00,DOMINICA
20,SSSSS,20000.00,JAMAICA

Copy the data file to HDFS location '/hivedb/testdb/employee_plain_table'
```
./hadoop fs -put ~/so/data.txt /hivedb/testdb/employee_plain_table
```
Run a select * command over testdb.Employee_plain_table
```
select * from testdb.Employee_plain_table;
```
This should display 20 records.
Use an insert command
```
insert overwrite table testdb.employee select * from employee_plain_table;
```
This should run a map reduce job and insert the records to bucketed table.

This will create 5 files as we have 5 buckets as per the DDL of employee table.

Verify this using command:

./hadoop fs -ls /hivedb/testdb/employee
Found 5 items
-rwxr-xr-x   1 hduser supergroup 95 2017-10-19 11:04 /hivedb/testdb/employee/000000_0
-rwxr-xr-x   1 hduser supergroup 81 2017-10-19 11:04 /hivedb/testdb/employee/000001_0
-rwxr-xr-x   1 hduser supergroup 90 2017-10-19 11:05 /hivedb/testdb/employee/000002_0
-rwxr-xr-x   1 hduser supergroup 88 2017-10-19 11:05 /hivedb/testdb/employee/000003_0
-rwxr-xr-x   1 hduser supergroup 84 2017-10-19 11:05 /hivedb/testdb/employee/000004_0

Open up each file, compare with the original data file and you will get to know what has happened.

Hope this clarifies your query! Reference: https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL+BucketedTables

Update: You used load with "local", it is only a copy operation i.e. it copies the given input file from source to destination location. Load command from "local" is a copy, and the one from "hdfs" is a move operation. No mapreduce is involved, so no bucketing happened.

Structure Difference between partitioning and bucketing in hive

2 Answers