Unable to read metadata during the process or Slow?

Question

I am trying to write metadata to hundreds of files at a time. I need to me able to write and read back the updated metadata in the same process.Say like add the last name to the photo title then append the first name to the title. Each piece of data is another operation that can be set to overwrite or append to a certain field.
The problem is when I enclose the entire operation inside a withWriteAccessDo block. In this case if I overwrite that title field with the last name and thend in the next operation I try to append the first name. The problem is that it does not get the updated metadata in the title field, it returns the orginal value!
I can fix it by putting the withWriteAccessDo block inside the operation for loop so during each operations it uses a new withWriteAccessDo block. This way the updated metadata can be read back for the append correctly. The problem with this meathod is that it takes a very long time! like hours! before in Lightroom 2 this whole operation would take place in under 30 seconds and now it takes and hour!
So here is some pusdocode
1 does not get old data correctly
withWriteAccessDo
     For each operation
          if overwite
               write data to field
          else if append
               get current filed data
               concat old data with data to be added
               write new data
          end
     loop
end withWriteAccessDo
2 works but takes a long time
For each operation
     withWriteAccessDo
          if overwite
               write data to field
          else if append
               get current filed data
               concat old data with data to be added
               write new data
          end
     end withWriteAccessDo
loop
Anything that I am doing wrong?

Answer 1

Lightrooom has been extensively reworked under the hood as far as catalog writes go.
Before: writes just wrote.
Now: All writes are accumulated in a transaction but are not committed (and hence not accessible) until exiting the with-write gate. And,
complete undo info is saved for every write.
So, what I do for effiiciency is either:
1) Make "to-do" functions
2) Save "to-do" info.
Then, call all these "to-do" functions, or process all this saved "to-do" info in a single write-gate, or in a succession of dependent write-gates.
Rob