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Previously, for a partitioned file, a range request using an index that did not search in partition-index order requires that certain key operations examine all active partitions to determine the correct result. For a partitioned index within a range request, the partition logic now takes advantage of the range conditions to restrict, if possible, the number of partitions that must be examined. The result of this enhancement is an increase in performance when searching data within the partitions.
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After purging a partition member, that partition number is no longer available for use, as the member is marked purged. The partition administration function PartAdmin(), had originally stubbed in a reuse mode, however, it was not implemented, and this mode is now available for use. The ptADMINreuse mode only supports reuse of a previously purged partition member.
As part of this change, partition instance numbers are introduced such that the host file can distinguish between different versions of the same partition. By “same” partition we mean partitions that contain the same range of partition key values. Reasons for having different versions of the same partition include purging a partition and then recreating the partition, or rebuilding a file partition (that could result in modified contents). The instance numbers are used in the host’s global unique index (GUIx), if any.
A GUIx contains key values from all partitions as a means of ensuring global uniqueness for a key value across all the partitions. The key value is stored in the GUIx, however, instead of storing a record location to go with the key, we stored the partition number that holds the record. This way, if we purge a partition, we do not need to find all the entries in the GUIx that correspond to the partition because if we find a duplicate conflict when trying to add a new key value, we can check if the existing key value is for a purged partition, and, if so, we can replace it by the new key value for an active partition.
The new implementation now stores not only the partition number in the GUIx, but also the instance number (that defaults to zero). Now it is not only possible to distinguish between purged and active partitions in the GUIx, we can also distinguish between a purged and recreated partition since we force them to have different instance numbers.
For non-huge files, the instance numbers are in the range of 0 to 255. Huge files use four bytes for the instance number.
The ptADMINbase mode behavior has also been improved such that it is possible to change the base raw partition number (that is, the lowest permitted partition number) to any desired value as long as it does not exceed any active partition. Instance numbers permit purged partitions to fall outside the new base number because we can distinguish between different versions of the partitions.
When a partition is opened, its instance number is checked against the host list of instance numbers by partition. If they don’t match the open fails with error PNST_ERR (927).
Note: The addition of instance numbers has caused the partition resource stored in the host data file to be revised, and assigned a version number 2. Prior code will not be able to open a partition file with a version 2 resource, and will fail with error PVRN_ERR (725).
