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hadoophivesqoop

what is the relevence of -m 1

I am executing below sqoop command::=

sqoop import --connect 'jdbc:sqlserver://10.xxx.xxx.xx:1435;database=RRAM_Temp' --username DRRM_DATALOADER --password ****** --table T_VND --hive-import --hive-table amitesh_db.amit_hive_test --as-textfile --target-dir amitesh_test_hive -m 1

I have two queries::-

1) what is the relevence of -m 1? as far as I know Its the number of mapper that I am assigning to the sqoop job. If that is true, then, the moment I assign -m 2, the execution start throwing error as below:

ERROR tool.ImportTool: Error during import: No primary key could be found for table xxx. Please specify one with --split-by or perform a sequential import with '-m 1'

Now, I am forced to change my concept, now I see, it has something to do with database primary key. Can somebody help me a logic behind this?

2) I have ordered the above sqoop command to save the file as text file format.But when I go to the location suggested by the execution, I find tbl_name.jar. Why, if --as-textfile is a wrong sytax, then what is the right one. Or is there any other location that I can find the file in?

Solution

  • 1) To have -m or --num-mappers to be set to a value greater than 1, the table must either have PRIMARY KEY or the sqoop command must be provided with a --split-by column. Controlling Parallelism would explain the logic behind this.

    2) The FileFormat of the data imported into the Hive table amit_hive_test would be plain text(--as-textfile). As this is --hive-import, the data will be first imported into the --target-dir and then is loaded (LOAD DATA INPATH) into the Hive table. The resultant data will be inside the table's LOCATION and not in --target-dir.