Tweak btree node splitting method

When splitting nodes (because they overflow), instead of having all new nodes with a full size and one with a smaller size, try to leave them all not more than half-full.
Experiments (including evperf datasets) showed that this is benefical for incremental index updates (random inserts/updates), as it makes fragmentation grow more slowly and speedups a little inserts/updates and btree lookups.

Example:

Before

1> btree_bench:test(2000000, 500000, 1000, "/home/fdmanana/tmp/foo.couch").
Creating btree with initial number of items 2000000, batch size 5000, random batches
Btree created in 276553.336 ms
Btree stats after creation:
btree_size 16684244
file_size 1317839559
fragmentation 98.73397001280942
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2000000
kp_nodes 628
kv_nodes 32865
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 107
min_elements_per_kp_node 1
avg_elements_per_kp_node 53.3312101910828
elements_per_kp_node_90_percentile 96
elements_per_kp_node_95_percentile 99
elements_per_kp_node_99_percentile 106
max_elements_per_kv_node 162
min_elements_per_kv_node 2
avg_elements_per_kv_node 60.85501293169025
elements_per_kv_node_90_percentile 131
elements_per_kv_node_95_percentile 145
elements_per_kv_node_99_percentile 159
max_kp_node_size 4602
min_kp_node_size 44
avg_kp_node_size 2294.2420382165606
kp_node_size_90_percentile 4129
kp_node_size_95_percentile 4258
kp_node_size_99_percentile 4559
max_compressed_kp_node_size 2038
min_compressed_kp_node_size 43
avg_compressed_kp_node_size 1034.7420382165606
compressed_kp_node_size_90_percentile 1825
compressed_kp_node_size_95_percentile 1882
compressed_kp_node_size_99_percentile 2010
max_kv_node_size 4375
min_kv_node_size 55
avg_kv_node_size 1644.0853491556368
kv_node_size_90_percentile 3538
kv_node_size_95_percentile 3916
kv_node_size_99_percentile 4294
max_compressed_kv_node_size 1239
min_compressed_kv_node_size 37
avg_compressed_kv_node_size 479.60921953445916
compressed_kv_node_size_90_percentile 991
compressed_kv_node_size_95_percentile 1094
compressed_kv_node_size_99_percentile 1193
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2000 keys)
Percentiles for single key lookups, 90% -> 1.539ms, 95% -> 6.763ms, 99% -> 12.805ms

Compacting btree
Btree compaction took 57355.094 ms
Btree stats after compaction:
btree_size 15269217
file_size 15269217
fragmentation 0.0
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2000000
kp_nodes 123
kv_nodes 12500
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 105
min_elements_per_kp_node 2
avg_elements_per_kp_node 102.6178861788618
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 160
min_elements_per_kv_node 160
avg_elements_per_kv_node 160.0
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4516
min_kp_node_size 87
avg_kp_node_size 4413.569105691057
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1686
min_compressed_kp_node_size 72
avg_compressed_kp_node_size 1347.2113821138212
compressed_kp_node_size_90_percentile 1394
compressed_kp_node_size_95_percentile 1401
compressed_kp_node_size_99_percentile 1417
max_kv_node_size 4321
min_kv_node_size 4321
avg_kv_node_size 4321.0
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 1183
avg_compressed_kv_node_size 1199.90384
compressed_kv_node_size_90_percentile 1210
compressed_kv_node_size_95_percentile 1211
compressed_kv_node_size_99_percentile 1214
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2000 keys)
Percentiles for single key lookups, 90% -> 1.395ms, 95% -> 1.567ms, 99% -> 1.88ms

Starting incremental inserts of 500000 new items, in random batches of size 5000
Incremental inserts took 36789.824 ms
Btree stats after inserts:
btree_size 19447730
file_size 180187724
fragmentation 89.20696173508468
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 320
kv_nodes 20791
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 106
min_elements_per_kp_node 1
avg_elements_per_kp_node 65.96875
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 162
min_elements_per_kv_node 2
avg_elements_per_kv_node 120.24433649175124
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4559
min_kp_node_size 44
avg_kp_node_size 2837.65625
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1995
min_compressed_kp_node_size 44
avg_compressed_kp_node_size 1029.378125
compressed_kp_node_size_90_percentile 1394
compressed_kp_node_size_95_percentile 1457
compressed_kp_node_size_99_percentile 1551
max_kv_node_size 4375
min_kv_node_size 55
avg_kv_node_size 3247.5970852772834
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 39
avg_compressed_kv_node_size 911.1964792458275
compressed_kv_node_size_90_percentile 1209
compressed_kv_node_size_95_percentile 1210
compressed_kv_node_size_99_percentile 1213
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 1.47ms, 95% -> 1.603ms, 99% -> 4.404ms

Starting incremental updates of every 5th item in the btree, in batches of size 5000 (500000 items), random order
Incremental updates took 61793.899 ms
Btree stats after updates:
btree_size 19447730
file_size 180187724
fragmentation 89.20696173508468
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 320
kv_nodes 20791
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 106
min_elements_per_kp_node 1
avg_elements_per_kp_node 65.96875
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 162
min_elements_per_kv_node 2
avg_elements_per_kv_node 120.24433649175124
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4559
min_kp_node_size 44
avg_kp_node_size 2837.65625
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1995
min_compressed_kp_node_size 44
avg_compressed_kp_node_size 1029.378125
compressed_kp_node_size_90_percentile 1394
compressed_kp_node_size_95_percentile 1457
compressed_kp_node_size_99_percentile 1551
max_kv_node_size 4375
min_kv_node_size 55
avg_kv_node_size 3247.5970852772834
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 39
avg_compressed_kv_node_size 911.1964792458275
compressed_kv_node_size_90_percentile 1209
compressed_kv_node_size_95_percentile 1210
compressed_kv_node_size_99_percentile 1213
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 1.053ms, 95% -> 1.232ms, 99% -> 4.041ms

Compacting btree
Btree compaction took 12494.651 ms
Btree stats after compaction:
btree_size 19088176
file_size 19088176
fragmentation 0.0
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 152
kv_nodes 15625
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 105
min_elements_per_kp_node 2
avg_elements_per_kp_node 103.78947368421052
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 160
min_elements_per_kv_node 160
avg_elements_per_kv_node 160.0
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4516
min_kp_node_size 87
avg_kp_node_size 4463.9473684210525
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1686
min_compressed_kp_node_size 75
avg_compressed_kp_node_size 1361.5394736842106
compressed_kp_node_size_90_percentile 1392
compressed_kp_node_size_95_percentile 1400
compressed_kp_node_size_99_percentile 1417
max_kv_node_size 4321
min_kv_node_size 4321
avg_kv_node_size 4321.0
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 1183
avg_compressed_kv_node_size 1200.02208
compressed_kv_node_size_90_percentile 1210
compressed_kv_node_size_95_percentile 1211
compressed_kv_node_size_99_percentile 1214
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 1.018ms, 95% -> 1.169ms, 99% -> 1.498ms

ok
2>

After

1> btree_bench:test(2000000, 500000, 1000, "/home/fdmanana/tmp/foo.couch").
Creating btree with initial number of items 2000000, batch size 5000, random batches
Btree created in 268182.733 ms
Btree stats after creation:
btree_size 16422278
file_size 1218231774
fragmentation 98.65195783343606
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2000000
kp_nodes 662
kv_nodes 28530
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 107
min_elements_per_kp_node 1
avg_elements_per_kp_node 44.095166163142
elements_per_kp_node_90_percentile 78
elements_per_kp_node_95_percentile 93
elements_per_kp_node_99_percentile 102
max_elements_per_kv_node 162
min_elements_per_kv_node 1
avg_elements_per_kv_node 70.10164738871363
elements_per_kv_node_90_percentile 136
elements_per_kv_node_95_percentile 146
elements_per_kv_node_99_percentile 158
max_kp_node_size 4602
min_kp_node_size 44
avg_kp_node_size 1897.0921450151056
kp_node_size_90_percentile 3355
kp_node_size_95_percentile 4000
kp_node_size_99_percentile 4387
max_compressed_kp_node_size 2225
min_compressed_kp_node_size 43
avg_compressed_kp_node_size 882.0135951661631
compressed_kp_node_size_90_percentile 1529
compressed_kp_node_size_95_percentile 1776
compressed_kp_node_size_99_percentile 1977
max_kv_node_size 4375
min_kv_node_size 28
avg_kv_node_size 1893.7444794952683
kv_node_size_90_percentile 3673
kv_node_size_95_percentile 3943
kv_node_size_99_percentile 4267
max_compressed_kv_node_size 1234
min_compressed_kv_node_size 25
avg_compressed_kv_node_size 546.8209954433929
compressed_kv_node_size_90_percentile 1028
compressed_kv_node_size_95_percentile 1103
compressed_kv_node_size_99_percentile 1189
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2000 keys)
Percentiles for single key lookups, 90% -> 1.301ms, 95% -> 4.603ms, 99% -> 12.706ms

Compacting btree
Btree compaction took 62111.127 ms
Btree stats after compaction:
btree_size 15269217
file_size 15269217
fragmentation 0.0
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2000000
kp_nodes 123
kv_nodes 12500
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 105
min_elements_per_kp_node 2
avg_elements_per_kp_node 102.6178861788618
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 160
min_elements_per_kv_node 160
avg_elements_per_kv_node 160.0
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4516
min_kp_node_size 87
avg_kp_node_size 4413.569105691057
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1686
min_compressed_kp_node_size 72
avg_compressed_kp_node_size 1347.2113821138212
compressed_kp_node_size_90_percentile 1394
compressed_kp_node_size_95_percentile 1401
compressed_kp_node_size_99_percentile 1417
max_kv_node_size 4321
min_kv_node_size 4321
avg_kv_node_size 4321.0
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 1183
avg_compressed_kv_node_size 1199.90384
compressed_kv_node_size_90_percentile 1210
compressed_kv_node_size_95_percentile 1211
compressed_kv_node_size_99_percentile 1214
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2000 keys)
Percentiles for single key lookups, 90% -> 1.324ms, 95% -> 1.45ms, 99% -> 1.849ms

Starting incremental inserts of 500000 new items, in random batches of size 5000
Incremental inserts took 36604.463 ms
Btree stats after inserts:
btree_size 19431715
file_size 171302728
fragmentation 88.65650580882752
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 279
kv_nodes 20419
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 106
min_elements_per_kp_node 1
avg_elements_per_kp_node 74.18279569892474
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 162
min_elements_per_kv_node 1
avg_elements_per_kv_node 122.43498702189137
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4559
min_kp_node_size 44
avg_kp_node_size 3190.8602150537636
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 2018
min_compressed_kp_node_size 45
avg_compressed_kp_node_size 1159.6810035842293
compressed_kp_node_size_90_percentile 1592
compressed_kp_node_size_95_percentile 1790
compressed_kp_node_size_99_percentile 1923
max_kv_node_size 4375
min_kv_node_size 28
avg_kv_node_size 3306.744649591067
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1230
min_compressed_kv_node_size 29
avg_compressed_kv_node_size 927.4621675890103
compressed_kv_node_size_90_percentile 1209
compressed_kv_node_size_95_percentile 1210
compressed_kv_node_size_99_percentile 1213
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 1.115ms, 95% -> 1.264ms, 99% -> 3.103ms

Starting incremental updates of every 5th item in the btree, in batches of size 5000 (500000 items), random order
Incremental updates took 58408.701 ms
Btree stats after updates:
btree_size 19431715
file_size 171302728
fragmentation 88.65650580882752
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 279
kv_nodes 20419
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 106
min_elements_per_kp_node 1
avg_elements_per_kp_node 74.18279569892474
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 162
min_elements_per_kv_node 1
avg_elements_per_kv_node 122.43498702189137
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4559
min_kp_node_size 44
avg_kp_node_size 3190.8602150537636
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 2018
min_compressed_kp_node_size 45
avg_compressed_kp_node_size 1159.6810035842293
compressed_kp_node_size_90_percentile 1592
compressed_kp_node_size_95_percentile 1790
compressed_kp_node_size_99_percentile 1923
max_kv_node_size 4375
min_kv_node_size 28
avg_kv_node_size 3306.744649591067
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1230
min_compressed_kv_node_size 29
avg_compressed_kv_node_size 927.4621675890103
compressed_kv_node_size_90_percentile 1209
compressed_kv_node_size_95_percentile 1210
compressed_kv_node_size_99_percentile 1213
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 1.433ms, 95% -> 1.599ms, 99% -> 3.0ms

Compacting btree
Btree compaction took 12399.026 ms
Btree stats after compaction:
btree_size 19088176
file_size 19088176
fragmentation 0.0
kv_chunk_threshold 7168
kp_chunk_threshold 6144
kv_count 2500000
kp_nodes 152
kv_nodes 15625
max_depth 4
min_depth 4
avg_depth 4.0
depth_90_percentile 4
depth_95_percentile 4
depth_99_percentile 4
max_reduction_size 8
min_reduction_size 8
avg_reduction_size 8.0
reduction_size_90_percentile 8
reduction_size_95_percentile 8
reduction_size_99_percentile 8
max_elements_per_kp_node 105
min_elements_per_kp_node 2
avg_elements_per_kp_node 103.78947368421052
elements_per_kp_node_90_percentile 105
elements_per_kp_node_95_percentile 105
elements_per_kp_node_99_percentile 105
max_elements_per_kv_node 160
min_elements_per_kv_node 160
avg_elements_per_kv_node 160.0
elements_per_kv_node_90_percentile 160
elements_per_kv_node_95_percentile 160
elements_per_kv_node_99_percentile 160
max_kp_node_size 4516
min_kp_node_size 87
avg_kp_node_size 4463.9473684210525
kp_node_size_90_percentile 4516
kp_node_size_95_percentile 4516
kp_node_size_99_percentile 4516
max_compressed_kp_node_size 1686
min_compressed_kp_node_size 75
avg_compressed_kp_node_size 1361.5394736842106
compressed_kp_node_size_90_percentile 1392
compressed_kp_node_size_95_percentile 1400
compressed_kp_node_size_99_percentile 1417
max_kv_node_size 4321
min_kv_node_size 4321
avg_kv_node_size 4321.0
kv_node_size_90_percentile 4321
kv_node_size_95_percentile 4321
kv_node_size_99_percentile 4321
max_compressed_kv_node_size 1228
min_compressed_kv_node_size 1183
avg_compressed_kv_node_size 1200.02208
compressed_kv_node_size_90_percentile 1210
compressed_kv_node_size_95_percentile 1211
compressed_kv_node_size_99_percentile 1214
max_key_size 16
min_key_size 16
avg_key_size 16.0
key_size_90_percentile 16
key_size_95_percentile 16
key_size_99_percentile 16
max_value_size 6
min_value_size 6
avg_value_size 6.0
value_size_90_percentile 6
value_size_95_percentile 6
value_size_99_percentile 6

Doing key lookups for every 1000th key (2500 keys)
Percentiles for single key lookups, 90% -> 0.943ms, 95% -> 1.106ms, 99% -> 1.396ms

ok