From 3539f6b895814ad79c455f7fe633ce253c77c140 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Mon, 5 May 2003 22:22:10 +0000 Subject: SF patch #729395: Dictionary tuning * Increase dictionary growth rate resulting in more sparse dictionaries, fewer lookup collisions, increased memory use, and better cache performance. For dicts with over 50k entries, keep the current growth rate in case an application is suffering from tight memory constraints. * Set the most common case (no resize) to fall-through the test. --- Objects/dictobject.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/Objects/dictobject.c b/Objects/dictobject.c index f0e93f8..f3adc0b 100644 --- a/Objects/dictobject.c +++ b/Objects/dictobject.c @@ -531,17 +531,23 @@ PyDict_SetItem(register PyObject *op, PyObject *key, PyObject *value) Py_INCREF(value); Py_INCREF(key); insertdict(mp, key, hash, value); - /* If we added a key, we can safely resize. Otherwise skip this! - * If fill >= 2/3 size, adjust size. Normally, this doubles the - * size, but it's also possible for the dict to shrink (if ma_fill is - * much larger than ma_used, meaning a lot of dict keys have been - * deleted). + /* If we added a key, we can safely resize. Otherwise just return! + * If fill >= 2/3 size, adjust size. Normally, this doubles or + * quaduples the size, but it's also possible for the dict to shrink + * (if ma_fill is much larger than ma_used, meaning a lot of dict + * keys have been * deleted). + * + * Quadrupling the size improves average dictionary sparseness + * (reducing collisions) at the cost of some memory and iteration + * speed (which loops over every possible entry). It also halves + * the number of expensive resize operations in a growing dictionary. + * + * Very large dictionaries (over 50K items) use doubling instead. + * This may help applications with severe memory constraints. */ - if (mp->ma_used > n_used && mp->ma_fill*3 >= (mp->ma_mask+1)*2) { - if (dictresize(mp, mp->ma_used*2) != 0) - return -1; - } - return 0; + if (!(mp->ma_used > n_used && mp->ma_fill*3 >= (mp->ma_mask+1)*2)) + return 0; + return dictresize(mp, mp->ma_used*(mp->ma_used>50000 ? 2 : 4)); } int -- cgit v0.12