Analyzing Data on COS/CHDFS

Last updated: 2021-03-19 10:34:56

    This document describes more ways to use Impala based on COS with data from direct data insertion and COS.

    Preparations

    1. To access COS in the task, you need to create a bucket in COS first. To access CHDFS in the task, you need to create and mount a CHDFS instance. Make sure you have activated the Tencent Cloud service and created an EMR cluster.
    2. When creating your EMR cluster, select the Impala component on the software configuration page, select Enable COS on the basic configuration page, and enter your SecretId and SecretKey. You can find your SecretId and SecretKey at the API key management page. If you don't have a key, click Create Key to create one.
    3. Relevant software programs such as Impala are installed in the /usr/local/service/ directory of the CVM instance for the EMR cluster.

    Directions

    Log in to any node (preferably a master one) in the EMR cluster first. For more information on how to log in to EMR, see Logging in to Linux Instance Using Standard Login Method. You can choose to log in with WebShell. Click Login on the right of the desired CVM instance to enter the login page. The default username is root, and the password is the one you set when creating the EMR cluster. Once the correct information is entered, you can enter the command line interface.

    Run the following commands on the EMR command line to switch to the Hadoop user and connect to Impala:

    [root@172 ~]# su hadoop
    [hadoop@172 ~]$ impala-shel.sh -i $host:27001

    $host is the private IP of your Impala data node.

    Step 1. Create a table (record)

    [$host:27001 ] > create table record(id int, name string) row format delimited fields terminated by ',' stored as textfile location 'cosn://$bucketname/';
    Query: create table record(id int, name string) row format delimited fields terminated by ',' stored as textfile location 'cosn://$bucketname/'
    Fetched 0 row(s) in 3.07s
    Here, `$bucketname` is the name plus path of your COS bucket. If you use CHDFS, replace the `location` value with `ofs://$mountname/`, where `$mountname` is your CHDFS instance mount address plus path.
    View the table information and confirm that `location` is the COS path.
    [$host:27001 ] > show create table record2;
    Query: show create table record2
    +----------------------------------------------------------------------+
    | result                                                               |
    +----------------------------------------------------------------------+
    | CREATE TABLE default.record2 (                                       |
    |   id INT,                                                            |
    |   name STRING                                                        |
    | )                                                                    |
    | ROW FORMAT DELIMITED FIELDS TERMINATED BY ','                        |
    | WITH SERDEPROPERTIES ('field.delim'=',', 'serialization.format'=',') |
    | STORED AS TEXTFILE                                                   |
    | LOCATION 'cosn://$bucketname'                                 |
    | TBLPROPERTIES ('numFiles'='19', 'totalSize'='1870')                  |
    +----------------------------------------------------------------------+
    Fetched 1 row(s) in 5.90s

    Step 2. Insert data into the table

    [$host:27001] > insert into record values(1,"test");
    Query: insert into record values(1,"test")
    Query submitted at: 2020-08-03 11:29:16 (Coordinator: http://$host:27004)
    Query progress can be monitored at: http:/$host:27004/query_plan?query_id=b246d3194efb7a8f:bc60721600000000
    Modified 1 row(s) in 0.64s

    Step 3. Use Impala to query the table

    [$host:27001] > select * from record;
    Query: select * from record
    Query submitted at: 2020-08-03 11:29:31 (Coordinator: http://172.30.1.136:27004)
    Query progress can be monitored at: http://$host:27004/query_plan?query_id=8148da96f8c0d369:4b26432a00000000
    +----+---------+
    | id | name    |
    +----+---------+
    | 1  | test    |
    +----+---------+
    Fetched 1 row(s) in 0.37s

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