What is Column Storage in Hana & how it is faster?

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Column store is divided into three parts: i) Main ii) L2 Delta iii) L1 Delta/cache.

  • Persisted data are saved in Main Memory.
  • Buffer and transaction changes are kept in L2 Delta and High Inserts / Deletes / Updates etc in L1 Delta.

L1-delta
– accepts all incoming data requests
– stores records in row format (write-optimized)
• fast insert and delete
• fast field update
• fast record projection
– no data compression
– holds 10,000 to 100,000 rows per single-node

L2-delta
– the second stage of the record life cycle
– stores records in column format
– dictionary encoding for better memory usage
– unsorted dictionary
• requiring secondary index structures to optimally
support point query access patterns
– well suited to store up to 10 million rows

Main
– final data format
– stores records in column format
– highest compression rate
• sorted dictionary
• positions in dictionary stored in a bit-packed manner
• the dictionary is also compressed

So the smart innovation of L1, L2 and Main memory and combination of all three, make data read and write, really fast and effective.

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