Furthermore, a VACUUM operation is required in order to remove all records marked for deletion and also perform any resorting operations that may or may not be required. Redshift prevents write-write conflicts from happening by forcing a transaction to obtain a table-level write lock and only allowing a transaction to release all its write locks when the transaction either commits or aborts. In particular, transactions capture a snapshot of the latest committed version of the data at the time a SELECT query, a DML statement, ALTER TABLE statement, CREATE TABLE statement, DROP TABLE statement, or TRUNCATE TABLE statement is executed. For all columns other than the sort key or with types BOOLEAN, REAL, or DOUBLE, LZO is the default compression.Īlthough not explicitly stated, Redshift utilizes Multi Version Concurrency Control. Under this encoding, each block is compressed with a standard compression algorithm. Runlength is supported for all datatypes. ![]() A separate dictionary of unique values is also created for each 1MB block. Runlengthįor each 1MB block on disk, consecutive values are replaced with a corresponding token that indicates the number of repetitions and the value repeated. MOSTLY16 supports INT, BIGINT, and DECIMAL. MOSTLY8 supports SMALLINT, INT, BIGINT, and DECIMAL. In the event that the value cannot be compressed, the original raw value is stored. This encoding utilizes packing to reduce storage. Any difference greater than the delta representable is stored raw along with a 1 byte flag. Redshift supports two delta variations, DELTA (supports SMALLINT, INT, BIGINT, DATE, TIMESTAMP, DECIMAL) which stores difference as 1-byte values and DELTA32K ( INT, BIGINT, DATE, TIMESTAMP, DECIMAL) which stores the difference as 2-byte values. Deltaįor each 1MB block on disk, data is stored as the difference relative to the previous value in series. This encoding is primarily suited for columns containing a limited number of character values and does not support BOOLEAN datatypes. If there are more than 256 unique column data values in a block, any unique data values beyond the first 256 are stored raw. In the original data, those values are replaced with the corresponding single byte. Byte-Dictionaryįor each 1MB block on disk, a dictionary a created which maps the first 256 unique column values to a single byte. By default, no compression is applied to values of columns defined as the sort key and values of BOOLEAN, REAL, or DOUBLE datatypes. ![]() ![]() Redshift allows for the following possible compression options. Column compression will be automatically applied when loading data into Redshift using the COPY command but can also be selected manually. This allows for reduced disk I/O and improves query performance. Redshift allows for the columns to be compressed, reducing data size and storing more data within each disk block. After subsequent development by Amazon and integration with AWS, Amazon Redshift was officially announced at the AWS re:invent 2012 conference and, after a limited preview, was released to the general public in February 2013.ĭictionary Encoding Delta Encoding Run-Length Encoding Naïve (Page-Level) Bit Packing / Mostly Encoding In exchange for its investment, Amazon acquired license rights to ParAccel's database system which would form the foundation of Amazon's own data warehouse solution: Amazon Redshift. In July 2011, Amazon invested in ParAccel, a software company that developed a shared-nothing architecture relational database system for analytics and business intelligence.
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