hadoop

Impala – Create Table AS Select * FROM Table – is SLOW

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Below query seems like the simplest way to create a replica of table. But simplicity comes with some cost as well. Above query will : NOT create partitions if there are any on TABLE_NAME_2 run very slow Instead of above we should follow following 2 way approach :  CREATE TABLE TABLE_NAME    Like TABLE_NAME_2;  — … Read more

HDFS – Data Movement across clusters

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You can move data in HDFS cluster using distcp command. distcp uses 10 mappers by default to bring data from source system. While doing data movement I encountered a problem in which data movement was failing because of checksum mismatch. If any block mismatch in the checksum then the complete data block was getting discarded.  Checksum is … Read more

Impala – Optimise query when using to_utc_timestamp() function

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From 40 minutes to just 4 minutes Impala to_utc_timestamp() function is used to convert date/timestamp timezone to UTC. But it works very slow. If you have less data in table even then you can easily notice its slow performance.  I faced a similar issue and noticed it was taking around 40 minutes alone to complete … Read more

Sqoop – Optimise Import

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Importing data using Sqoop is one of the most time consuming task of BigData environment. Sqoop is a powerful yet simple tool to import data from different RDBMSs into HDFS. But while importing data following 2 points should be considered with higher priority to reduce time : Number of Mappers: Mapper provides parallelism while importing … Read more

Sqoop – Handle NULL values

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By default Sqoop import NULL as null, if you want to change this default configuration you can use following arguments. While importing data :  –null-string –null-non-string While exporting data :  –input-null-string –input-null-non-string Check this example for more clarification :  In above example : –null-string argument represents what should be writtern in HDFS whenever a NULL is identified in … Read more