Retrieving time for default Btree and time sorted Btree

Question

Hi all,
I am working on FreeBsd and Berkeley DB 4.5.20
I have 2 kind of Btree databases and I want to measure the time for sequentially retrieving of all records.
1. Btrees with fixed record size of 128 Byte
2. Btrees with variable record size of around 630KB
when I sort the order of the Db's by time (time is the key in my DB's) the retrieving time is much shorter, so i have a higher performance.
but when I see the statistics structures:
for the 1. group after sorting by time the internal page fill factor and leaf pages fill factor are like 94% or 98% and overflow ff is 0%. so I an understand that this result in a higher performance.
and i have a shorter retrieving time than before sorting by time.
but for the 2. group that means for variable large record sizes I have shorter retrieving time (higher performance) before sorting by time but lower leaf and internal page fillfactor. and after sorting higher leaf and internal page ff but longer retrieving time. and the overflow ff is before and after sorting 99%.
so I am confuse , because I thought the higher leaf and internal page ff the higher performance,
but this is exactly the opposite for large variable record sizes. is that because of the high overflow page ff?
I would appreciate if some could explain it to me.
Regards
soudi

Answer 1

hi Bogdan,
there are the statistics,
Btree with variable large record sizes:
53162 Btree magic number
9 Btree version number
Little-endian Byte order
duplicates Flags
2 Minimum keys per-page
4096 Underlying database page size
2 Number of levels in the tree
357 Number of unique keys in the tree
1165 Number of data items in the tree
1 Number of tree internal pages
3930 Number of bytes free in tree internal pages (4% ff)
8 Number of tree leaf pages
11064 Number of bytes free in tree leaf pages (66% ff)
0 Number of tree duplicate pages
0 Number of bytes free in tree duplicate pages (0% ff)
180832 Number of tree overflow pages
1641148 Number of bytes free in tree overflow pages (99% ff)
0 Number of empty pages
0 Number of pages on the free list
it took 35.77492 seconds.
average data.size : 630KB
sorted Btree with variable large record sizes
53162 Btree magic number
9 Btree version number
Little-endian Byte order
Flags
2 Minimum keys per-page
4096 Underlying database page size
2 Number of levels in the tree
1165 Number of unique keys in the tree
1165 Number of data items in the tree
1 Number of tree internal pages
3600 Number of bytes free in tree internal pages (12% ff)
13 Number of tree leaf pages
1650 Number of bytes free in tree leaf pages (96% ff)
0 Number of tree duplicate pages
0 Number of bytes free in tree duplicate pages (0% ff)
180832 Number of tree overflow pages
1641148 Number of bytes free in tree overflow pages (99% ff)
0 Number of empty pages
0 Number of pages on the free list
it took 77.556531 seconds.
average data.size : 630KB
Btree with fixed short record sizes
53162 Btree magic number
9 Btree version number
Little-endian Byte order
duplicates Flags
2 Minimum keys per-page
4096 Underlying database page size
2 Number of levels in the tree
4141 Number of unique keys in the tree
1347892 Number of data items in the tree
3626 Number of tree internal pages
14M Number of bytes free in tree internal pages (3% ff)
161 Number of tree leaf pages
416126 Number of bytes free in tree leaf pages (36% ff)
48079 Number of tree duplicate pages
15M Number of bytes free in tree duplicate pages (92% ff)
0 Number of tree overflow pages
0 Number of bytes free in tree overflow pages (0% ff)
0 Number of empty pages
0 Number of pages on the free list
it took 87.89131 seconds.
data.size : 128Byte
sorted Btree with fixed short record sizes
53162 Btree magic number
9 Btree version number
Little-endian Byte order
Flags
2 Minimum keys per-page
4096 Underlying database page size
4 Number of levels in the tree
1347892 Number of unique keys in the tree
1347892 Number of data items in the tree
560 Number of tree internal pages
31078 Number of bytes free in tree internal pages (98% ff)
58604 Number of tree leaf pages
17M Number of bytes free in tree leaf pages (92% ff)
0 Number of tree duplicate pages
0 Number of bytes free in tree duplicate pages (0% ff)
0 Number of tree overflow pages
0 Number of bytes free in tree overflow pages (0% ff)
0 Number of empty pages
0 Number of pages on the free list
it took 22.453395 seconds.
data.size : 128Byte
my problem is why is unsorted Btree with variable large records faster dann the sorted, while the page fill factor is by sorted btree higher.
thanks
soudi