From: INADA Naoki Date: Tue, 17 Apr 2018 06:53:34 +0000 (+0900) Subject: bpo-33205: dict: Change GROWTH_RATE to `used*3` (GH-6350) X-Git-Tag: v3.8.0a1~1955 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=5fbc511f56688654a05b9eba23d140318bb9b2d5;p=python bpo-33205: dict: Change GROWTH_RATE to `used*3` (GH-6350) --- diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-04-03-00-58-41.bpo-33205.lk2F3r.rst b/Misc/NEWS.d/next/Core and Builtins/2018-04-03-00-58-41.bpo-33205.lk2F3r.rst new file mode 100644 index 0000000000..44511865ab --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2018-04-03-00-58-41.bpo-33205.lk2F3r.rst @@ -0,0 +1,3 @@ +Change dict growth function from ``round_up_to_power_2(used*2+hashtable_size/2)`` to +``round_up_to_power_2(used*3)``. Previously, dict is shrinked only when ``used == 0``. +Now dict has more chance to be shrinked. diff --git a/Objects/dictobject.c b/Objects/dictobject.c index be895d4c15..01d913bfce 100644 --- a/Objects/dictobject.c +++ b/Objects/dictobject.c @@ -396,17 +396,16 @@ dk_set_index(PyDictKeysObject *keys, Py_ssize_t i, Py_ssize_t ix) */ /* GROWTH_RATE. Growth rate upon hitting maximum load. - * Currently set to used*2 + capacity/2. + * Currently set to used*3. * This means that dicts double in size when growing without deletions, * but have more head room when the number of deletions is on a par with the - * number of insertions. - * Raising this to used*4 doubles memory consumption depending on the size of - * the dictionary, but results in half the number of resizes, less effort to - * resize. + * number of insertions. See also bpo-17563 and bpo-33205. + * * GROWTH_RATE was set to used*4 up to version 3.2. * GROWTH_RATE was set to used*2 in version 3.3.0 + * GROWTH_RATE was set to used*2 + capacity/2 in 3.4.0-3.6.0. */ -#define GROWTH_RATE(d) (((d)->ma_used*2)+((d)->ma_keys->dk_size>>1)) +#define GROWTH_RATE(d) ((d)->ma_used*3) #define ENSURE_ALLOWS_DELETIONS(d) \ if ((d)->ma_keys->dk_lookup == lookdict_unicode_nodummy) { \