The properties you can set are as follows:
Normally file space for DP4 databases is allocated only as it is required. On some operating systems, especially if you run REORGDB only rarely, this can cause your database to be fragmented and to perform poorly.
If you enable preallocation your database will be grown by progressively larger amounts each time more space is required. This may help the database to remain unfragmented.
This option, introduced in release 4.622, enables you to select between various database architectures that are now supported. In case of doubt, then unless you require compatibility with an earlier release, select "Two File Index". The help messages for the various options should help you decide what is best for you. You can also refer to "Configuring the Index Structure" on the DP4UG web site. Depending on the value you choose here, several, or even all, the remaining fields in the dialog may be disabled.
This option, introduced in release 4.622, and only enabled with the new database structures it introduces, controls the maximum possible size of your database IND file. The actual maximum index size depends both on this value, and the node size. The help message has a table showing how these values relate. The default value, of 3 bytes, is suffient for an index file of at least 8 Gigabytes, and up to 64 Gigabytes with the largest node size. In fact a value of 2 bytes is sufficient for index file up to 256MB if you use the largest node size.
Although picking a small value for this value will save some space in the index this is not likely to make a very noticeable difference, because probably around 90% of space in the index file is occupied by the keys of the records in the database. Also REORGDB cannot currently correct a value that is too small, as it can with the corresponding parameters for the data file. So err on the side of caution when selecting this value. You should allow a margin of at least 50% if you select a small value, because the index is reduced in size significantly during the "index optimisation" phase. Also your index file is liable to grow swiftly if you have applications that frequently delete and then reinsert large number of records.
Prior to release 4.620 the index node size was fixed at 512 bytes. With DP4 Enterprise releases it is possible to select the index node size. Based on the number n you enter the actual node size will be 2^n* 512 bytes, i.e. 0 gives 512 bytes, 1 1024 bytes, 2 2048 bytes, and 3 4096 bytes.
Choose 0 if you require your database to be compatible with earlier releases of DP4 (up to 4.523/4.619), or 16 bit versions of DP4.
The larger the value you select the smaller the database index file will be. With a size of 3 the index file may be be up to 15% smaller than it would be with index node size 0. Additionally your index will be flatter, and disk cache utilisation may be improved (because most operating systems divide files into 4096 byte pages), so database look up will be faster if performance of your database is disk bound. If your database is processor bound (likely for database index files not much larger than the size of the available memory) increasing the index node size may reduce performance slightly.
DP4 Enterprise can compress the index file more efficiently than earlier DP4 releases. It does this by removing trailing spaces from character key fields.
You must not select this option if any character key fields contain binary data that includes binary 0 (it does not matter if non key fields contain such data). Do not select this option if you require compatibility with earlier releases (though you can revert to the old index compression if required).
Select this option if you would like to enable the improved compression.
Although using this option reduces DAT file size substantially, so might appear to be useful for "program" databases you are distributing via some online upgrade process, the database DAT file will probably not be compressed nearly so well by software such as ZIP programs, so using it for this reason may not be a good idea.
If this option, introduced in release 4.622, and only available with the new database structures, is enabled, then the "rebuild data and index files" option of REORGDB will add information to the DCI (data compresesion information) file that will most records in the data file to be compressed to a very high degree. This option will cause some minor loss of performance, so should only be enabled where disk space is restricted, or the database is very large.
If you are unsure, what values you need for the data pointer and data sequence size, it is safe to set them both to a low value such as 2 or 3. REORGDB will increase your chosen values if need be.
This option, introduced in release 4.622, and only available with the new database structures, controls the maximum data file size. A value of 4 bytes, the default, is required for data files larger than !6 Megabytes, and suffices for data files up to 4 Gigabytes. A value of 3 bytes may be enough for "Program databases" and will reduce the size of the IND or PTR file slightly.
As of release 4.622, specifying the -ADVANCED command tail on the command line to REORGDB -DATA, will upgrade the database to use all the new structure features. On all substantial databases we have tried this with so far the final database has a DAT file at least two thirds smaller than the original database, and the index has usually been reduced in size by around 50%. If you specify the -TIGHT command tail as well, REORGDB will use the smallest safe values for the data pointer and sequence sizes.