Partial Access is not supported if Transactions are enabled!
In some scenarios, inserting or looking up a record in one single operation may be difficult - i.e. if the record is too big. For such cases applications can use “Partial Access” to a record. This can be used to read and write several chunks of a huge record, or to “stream” data from or to the Database.
With Partial Access, records can be read or written in several smaller
steps. If the flag
UPS_PARTIAL is specified in
ups_db_find (or one of the corresponding cursor functions), then
upscaledb will evaluate the fields
When writing a partial record, upscaledb will write
record->partial_size bytes of the record data at offset
record->partial_offset. The full record size will always be given in
record->size. When a record is overwritten (see
record->size, the record will grow or shrink.
When writing with an invalid combination (the sum of partial_offset +
partial_size exceeds the total record size), upscaledb will return
When reading a partial record, upscaledb will read
record->partial_size bytes of the record data starting at offset
record->partial_offset. The data will be stored in
size of the retrieved data is stored in
When reading a part of a record, and the partial_offset exceeds the
total record size, upscaledb will return
UPS_INV_PARAMETER. If the sum
of partial_offset + partial_size exceeds the total record size,
upscaledb will limit the partial_size and return the read size in
Partial access has a few limitations: it is not allowed in combination with
Transactions and it only works with all records that are larger than 8 bytes.
upscaledb has a very efficient and compact storage for small records
with a size <= 8 bytes. This storage does not support partial access.
The API therefore returns
UPS_INV_PARAMETER if the
8 and the flag
UPS_PARTIAL is set.