Also, please add the table (and the reasoning that led to it) to the PEP. On Fri, Aug 26, 2011 at 7:55 AM, Guido van Rossum <gu...@python.org> wrote: > It would be nice if someone wrote a test to roughly verify these > numbers, e.v. by allocating lots of strings of a certain size and > measuring the process size before and after (being careful to adjust > for the list or other data structure required to keep those objects > alive). > > --Guido > > On Fri, Aug 26, 2011 at 3:29 AM, "Martin v. Löwis" <mar...@v.loewis.de> wrote: >>> But strings are allocated via PyObject_Malloc(), i.e. the custom >>> arena-based allocator -- isn't its overhead (for small objects) less >>> than 2 pointers per block? >> >> Ah, right, I missed that. Indeed, those have no header, and the only >> overhead is the padding to a multiple of 8. >> >> That shifts the picture; I hope the table below is correct, >> assuming ASCII strings. >> 3.2: 7 pointers (adds 4 bytes padding on 32-bit systems) >> 393: 10 pointers >> >> string | 32-bit pointer | 32-bit pointer | 64-bit pointer >> size | 16-bit wchar_t | 32-bit wchar_t | 32-bit wchar_t >> | 3.2 | 393 | 3.2 | 393 | 3.2 | 393 | >> ----------------------------------------------------------- >> 1 | 40 | 48 | 40 | 48 | 64 | 88 | >> 2 | 40 | 48 | 48 | 48 | 72 | 88 | >> 3 | 40 | 48 | 48 | 48 | 72 | 88 | >> 4 | 48 | 48 | 56 | 48 | 80 | 88 | >> 5 | 48 | 48 | 56 | 48 | 80 | 88 | >> 6 | 48 | 48 | 64 | 48 | 88 | 88 | >> 7 | 48 | 48 | 64 | 48 | 88 | 88 | >> 8 | 56 | 56 | 72 | 56 | 96 | 86 | >> >> So 1-byte strings increase in size; very short strings increase >> on 16-bit-wchar_t systems and 64-bit systems. Short strings >> keep there size, and long strings save. >> >> Regards, >> Martin >> >> >> > > > > -- > --Guido van Rossum (python.org/~guido) >
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