tdb2: use expansion heuristics from tdb1
This reduces the amount of expansion we do.
Before:
./speed
1000000
Adding
1000000 records: 23210 ns (
59193360 bytes)
Finding
1000000 records: 2387 ns (
59193360 bytes)
Traversing
1000000 records: 2150 ns (
59193360 bytes)
Deleting
1000000 records: 13392 ns (
59193360 bytes)
Re-adding
1000000 records: 11546 ns (
59193360 bytes)
Appending
1000000 records: 29327 ns (
91193360 bytes)
Churning
1000000 records: 33026 ns (
91193360 bytes)
After:
$ ./speed
1000000
Adding
1000000 records: 17480 ns (
61472904 bytes)
Finding
1000000 records: 2431 ns (
61472904 bytes)
Traversing
1000000 records: 2194 ns (
61472904 bytes)
Deleting
1000000 records: 10948 ns (
61472904 bytes)
Re-adding
1000000 records: 11247 ns (
61472904 bytes)
Appending
1000000 records: 21826 ns (
96051424 bytes)
Churning
1000000 records: 27242 ns (
96051424 bytes)