How COPY uses real-time statistics

Real-time statistics in SYSIBM.SYSTABLESPACESTATS are used by the COPY utility when creating sequential image copies for table spaces.

Specifically, COPY uses the following columns in SYSTABLESPACESTATS:

• COPYUPDATEDPAGES is used to determine the number of pages updated since the last copy for incremental and CHANGELIMIT processing. This information is used to avoid allocation of the image copy data set when no pages have been updated or the CHANGELIMIT criteria is not met.

  When COPY is used with SHRLEVEL CHANGE, COPYUPDATEDPAGES includes the number of pages updated during and after the last copy. In this case, COPYUPDATEDPAGES might be indeterminate, because Db2 does not know whether pages updated during the last copy were included and therefore cannot reset COPYUPDATEDPAGES to zero during a subsequent incremental copy. In this case, when COPYUPDATEDPAGES remains non-zero, each space map page is checked for updated pages by incremental or CHANGELIMIT processing.

  If real-time statistics are not valid (for example, NULL) and the table space has the TRACKMOD YES attribute, COPY uses the object’s space map pages. For table spaces with the TRACKMOD NO attribute, COPY scans all of the pages.

• NACTIVE is used to estimate the size of the image copy data set. If NACTIVE is not valid (for example, NULL) COPY opens the table space and uses the size of the table space to estimate the size of the image copy data set.