Understanding the difference between Encoding and Compression in practical way

Hi Eli

Can you give me one query based example for ENCODING and COMPRESSION

With Regards

Ujjwal

Sure , Let’s take the DELTAVAL as an example:

Vertica  definition for  DELTAVAL is “data is recorded as a difference from the smallest value in the data block”  - let assumes your data block include sequential continues number .

let say , your data block include the below list of values :

1000,1004,1007,1008,1009 , with DELTAVAL Vertica will store something like this -> 1000, 4,3,1,1  , you can see it as kind of compression , but its not binary compression its more of applicable compression .

On top this applicable compression  , Vertica will used its internal binary compression (binary compression  can be gzip )    , at the end you end up  with two layers  of compression that provide very good compression ratio  .

In  the query  time , Vertica is able to know in which block the data is to be exists and able to decompress from binary mode   only the relevant blocks needed for the query  , in addition part of the execution  operators can still run on the encoded data  .  So getting good compression and optimized query execution  in both hands

I hope its more clear now

Thanks

Predicates on columns whose data is encoded in certain formats, such as run-length encoding, can be applied directly on the encoded data, thus bypassing the overhead of decompression and reducing the quantity of data to be copied and processed through the joins. This is particularly advantageous for low cardinality columns that are encoded.