How to Select the Best Compression Type in Amazon Redshift. If no compression is specified in a CREATE TABLE or ALTER TABLE statement, Amazon Redshift automatically assigns compression encoding as follows: Columns that are defined as sort keys are assigned RAW compression. When you don’t use compression, data consumes additional space and requires additional disk I/O. In AWS Redshift is now possible to alter ONLY VARCHAR column but under these conditions: You can’t alter a column with compression encodings BYTEDICT, RUNLENGTH, TEXT255, or TEXT32K. In AWS Redshift is now possible to alter ONLY VARCHAR column but under these conditions:. Applying compression to large uncompressed columns can have a big impact on your cluster. Amazon Redshift introduces AZ64, a new compression encoding for optimized storage and high query performance Posted On: Oct 8, 2019 AZ64, a proprietary compression encoding that is designed to achieve a high compression … You can't alter columns with default values. You can run ANALYZE COMPRESSION to get recommendations for each column encoding schemes, based on a sample data stored in redshift table. Specifying Column Compression Encoding. You define compression per column, if you do not specify any, Redshift uses the following compression: All columns in temporary tables are assigned RAW compression by default apply a compression type, or encoding, to the columns in a table manually when you create the table; use the COPY command to analyze and apply compression automatically (on an empty table) specify the encoding for a column when it is added to a table using the ALTER TABLE command; From the same documentation, You can't decrease the size less than maximum size of existing data. A compression encoding specifies the type of compression that is applied to a column of data values as rows are added to a table. Table compression recommendation. ALTER TABLE table-name ADD [ COLUMN ] column_name column_type ENCODE encoding-type; Compression Encodings: A compression encoding specifies the type of compression that is applied to a column of data values as rows are added to a table. Compression is defined per column allows reduction of size of stored data, which reduces disk I/O and improves query performance. Analyze Redshift Table Compression Types. Redshift package for dbt (getdbt.com). Amazon Redshift is optimized to reduce your storage footprint and improve query performance by using compression encodings. Amazon Redshift provides a very useful tool to determine the best encoding for each column in your table. ANALYZE COMPRESSION is an advisory tool and doesn’t modify the column encodings of the table. You can also see how long the export (UNLOAD) and import (COPY) lasted. The events table compression (see time plot) was responsible for the majority of this reduction. You can't decrease the size less than maximum size of existing data. You can’t alter a column with compression encodings BYTEDICT, RUNLENGTH, TEXT255, or TEXT32K. Tables compressions reduced total redshift disk usage from 60% to 35%. Luckily, you don’t need to understand all the different algorithms to select the best one for your data in Amazon Redshift. ALTER TABLE ALTER COLUMN type varchar(300); The above command will increase column size to Redshift tables and alter the column length, or column size as required. There is no TEXT column size in Redshift, so you can go to a maximum of 65535 , or simply specify the max alias. The table shows a disk space reduction of ~ 50% for these tables. Contribute to fishtown-analytics/redshift development by creating an account on GitHub. 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