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Data Compression Enhanced in Db2 12

September 12, 2017

Db2 12 function level V12R1M500 introduces the capability to compress LOB table space using zEnterprise data compression (zEDC) hardware. This IBM Redbook offers a detailed look at zEDC.

Data compression isn't exactly new, as Db2 10 brought limited capabilities. That release allows portions of the LOB column to be stored and compressed in the base table space. However, it isn't possible to compress the entire LOB in Db2 10, so zEDC compression is obviously a big step forward.

zEDC hardware is required to take advantage of zEDC compression. (This essentially replaces the compression dictionary, which is needed for LOB compression.) Beyond that, the base table space must be a universal table space (UTS).

While Db2 catalog LOB table spaces cannot be compressed, LOB table spaces owned by the Db2 directory can be compressed by enabling the COMPRESS_DIRLOB zparm. Data is compressed on DASD, in the buffer pool and on log.

If the LOB data is smaller than the page size of the LOB table space, the data will not be compressed. You may need to adjust the page size to achieve optimum results. DSN1COMP, an IBM-provided utility, can be used to help determine proper page size and project compression percentages.

Posted September 12, 2017| Permalink

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