The Row-Level Versioning (RLV) Store

Row-level versioning allows multiple transactions to modify different rows of the same table concurrently. The in-memory, write-optimized RLV store supplements the SAP Sybase IQ main store in providing concurrent read- and write-access to IQ base tables.

The IQ server provides the ability to configure, on a connection basis, single- or multiple-writer concurrent access to IQ base tables. Multiple connections can modify the same table, as long as they are adding or modifying different rows. Only tables which have RLV storage enabled are eligible for multiple-writer concurrent access.

The RLV store provides:

• Low latency writes with minimal index and compression overhead, resulting in efficient in-memory read/write operations
• Efficient concurrent updates with row versioning and minimal lock contention
• High performance column scans which feature in-memory read operations

The RLV store records incremental DML from an IQ table and automatically merges these changes into the IQ main store. The combined RLV and main stores are write-optimized for efficient DML and low latency data access, yet still have read-optimized on-disk query performance across the majority of data.

Whereas traditional, table-level versioned (TLV) tables reside only in the IQ main column store, row-level versioning (RLV) enabled tables reside in both the IQ main and RLV stores.

• The RLV Store Merge
  The RLV store is an autonomous self-managing, in-memory store that merges into the IQ main store automatically (either periodically or when thresholds are reached).
• RLV Store Partitioning
  All IQ base tables, whether unpartitioned, range-partitioned, hash-partitioned or range-hash partitioned, can be enabled for row-level versioning, however the in-memory RLV store portion is not partitioned.
• Table Fragments and Subfragments
  A table fragment is where data is stored. The fragment is further subdivided into subfragments. A table fragment may contain one or more subfragments.