Now when the 3rd storage type (radix tree) is all in, old
storage can be safely removed. The result is:
1. memory footprint
sizeof(class row): 112 => 16 bytes
sizeof(rows_entry): 126 => 120 bytes
the "in cache" value depends on the number of cells:
num of cells master patch
1 752 656
2 808 712
3 864 768
4 920 824
5 968 936
6 1136 992
...
16 1840 1672
17 1904 1992 (+88)
18 1976 2048 (+72)
19 2048 2104 (+56)
20 2120 2160 (+40)
21 2184 2208 (+24)
22 2256 2264 ( +8)
23 2328 2320
...
32 2960 2808
After 32 cells the storage switches into rbtree with
24-bytes per-cell overhead and the radix tree improvement
rocketlaunches
64 7872 6056
128 15040 9512
256 29376 18568
2. perf_mutation test is enhanced by this series and the
results differ depending on the number of columns used
tps value
--column-count master patch
1 59.9k 57.6k (-3.8%)
2 59.9k 57.5k
4 59.8k 57.6k
8 57.6k 57.7k <- eq
16 56.3k 57.6k
32 53.2k 57.4k (+7.9%)
A note on this. Last time 1-column test was ~5% worse which
was explained by inline storage of 5 cells that's present on
current implementation and was absent in radix tree.
An attempt to make inline storage for small radix trees
resulted in complete loss of memory footprint gain, but gave
fraction of percent to perf_mutation performance. So this
version doesn't have inline nodes.
The 1.2% improvement from v2 surprisingly came from the
tree::clone_from() which in v2 was work-around-ed by slow
walk+emplace sequence while this version has the optimized
API call for cloning.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
1bdfa355ea