The UDS online utility enables you to make changes to the physical properties of the data contained in the databases during normal DBH operation. In this case the contents of the user data can be neither seen nor changed in the UDS online utility.
All requested changes are performed by the DBH in transactions which are comparable to normal user transactions and are controlled solely by the UDS online utility. In this respect the UDS online utility behaves like a totally normal user program.
The UDS online utility offers the following functions in the form of new DMLs which modify the database itself or how it is processed:
With the online DML RELOCATE you relocate records and tables in a single realm. Here the occupancy ratio in the front part of the realm is generally increased. As a result, contiguous free data pages are created in the back part of the realm.
Furthermore, you can relieve the load on a realm by relocating pages of a distributable list to another realm. A description of the DML RELOCATE is provided in the section “DML RELOCATE - Relocating data pages”.With the online DML FPASCAN you change the settings for the free place search in the realm during live operation. A description of the DML FPASCAN is provided in the section “DML FPASCAN - Defining the search mode for the free place search”.
With the online DML PREFRLM you change the setting of the preferred realm for a distributable list. A description of the DML PREFRLM is provided in the section “DML PREFRLM - Defining the preferred realm for distributable lists”.
With the online DML REORGPPP you can update PPPs to the most recent values during live operation in a single realm. A description of the DML REORGPPP is provided in the section “DML REORGPPP – Reorganizing probable position pointers (PPPs)”.
In a UDS online utility procedure the RELOCATE, FPASCAN and PREFRLM functions always refer to a database which is identified unambiguously by the subschema and to a source realm. If multiple functions (RELOCATE, FPASCAN and PREFRLM) are to be executed in a UDS online utility procedure, the subschema name and realm name must be identical in each case in all these functions.
In order to make the requested changes in the transactions of the UDS online utility, resources must be used in the DBH in contention with the other application programs which are running in parallel (locks, I/O buffer, etc.). In order to avoid any negative repercussions on these applications, you should use the UDS online utility at times when the normal load and changes in the realm being processed by the UDS online utility tend to be low.
The statements of the UDS online utility enable you to control the scope of the changes which are to be performed in a transaction, thus permitting you to guarantee that application programs which execute in parallel are hindered very little. You can also use specific wait statuses to control the order of the various transactions of the UDS online utility to ensure that hindrances for applications which execute in parallel are reduced still further.
Overall it is not an aim to make all the changes requested with the UDS online utility in as short a time as possible. Rather, the aim is to deal with these in the smallest possible units and with as few repercussions as possible on applications which execute in parallel.
The various requests of the UDS online utility to the DBH supply information on the changes which have been made. You can use this information in turn for further control of the UDS online utility.
Multiple instances of the UDS online utility which make changes in different realms can be active at any given time.
Please note that the actions of the UDS online utility may result in the volume of the ALOG data becoming considerably greater, and take this into account when you plan the use of the UDS online utility.