The following information on database page formatting applies both to online realm extensions and realm extensions performed offline with the utility routine BREORG.
When the DBDIR is extended, the additional database pages are always formatted. This also applies to the DBCOM, even though it can only be extended offline.
When a user realm is extended, only the newly added database pages which may be referenced by probable position pointers (PPP) are formatted. All other newly added database pages are formatted individually the first time they are used. The number of database pages to be formatted significantly affects the time taken for a realm extension. The number of database pages to be formatted also significantly affects the size of the ALOG file. One, two or three 4KB blocks (for 2, 4 or 8KB databases) are written to the ALOG file for every page to be formatted, depending on the length of the database page. The number of database pages to be formatted should thus be kept as low as possible.
Probable position pointers (PPP) can potentially reference pages outside the database if a realm size has been reduced by the utility routine BREORG (MODIFY-REALM-SIZE statement). This is because, for reasons of performance, the individual probable position pointers (PPP) are not updated during size reduction. After realm size reductions, therefore, you should carry out BREORG runs with the statement REORGANIZE-POINTERS for all user realms.
PPPs can also be updated via REORGPPP DML in UDS online utility during ongoing operation. When all PPPs of all user realms are updated, formatting of new pages during an online realm extension can be avoided.
If the highest page to be formatted in a user realm (cf. HIGHEST PAGE NR FOR FORMATTING in the BPRECORD output of DISPLAY PAGE ZERO) is not greater than the number of pages in this realm, then no probable position pointers (PPP) point to any pages outside the database. Newly added database pages need not therefore be formatted during a realm extension, thus improving the performance of an online realm extension.
If the highest page to be formatted in a user realm is not yet known, it is sufficient to execute one BREORG run with the REORGANIZE-POINTERS statement for each realm of the database.
You can ascertain the formatting status of a realm with the utility routine BPRECORD (see the manual "Recovery, Information and Reorganization", and the section on BPRECORD).
You can find out whether or not a realm’s extension pages have to be formatted as follows:
using the utility routine BPRECORD (see the manual "Recovery, Information and Reorganization", BPRECORD).
with the DAL command DISPLAY INCR (see section "DISPLAY INCR - Show information on online extensibility of all activated realms in the database configuration" in chapter "Listing information on the DB configuration (DISPLAY)"). Information about whether formatting is necessary is output for all attached realms, thus allowing you to assess the effects of activating online realm extension.