I see the same result on Linux. However, stepping through the C code in the debugger indicates it passes repeatedly through Perl_pp_concat (pp_hot.c) and Perl_sv_grow (sv.c) and in Perl_sv_grow() it calls realloc here: 

    if (newlen > SvLEN(sv)) {           /* need more room? */
        newlen = PERL_STRLEN_ROUNDUP(newlen);
        if (SvLEN(sv) && s) {
#ifdef MYMALLOC
            const STRLEN l = malloced_size((void*)SvPVX_const(sv));
            if (newlen <= l) {
                SvLEN_set(sv, l);
                return s;
            } else
#endif
            s = saferealloc(s, newlen);

[download]
So it seems the performance of Perl string concatenation depends on the performance of the underlying C library realloc function. Now, I thought most reallocs would double the string size (for the reasons pointed out earlier by tye) so I'm a bit confused about the Devel::Size results. Haven't resorted to studying the glibc realloc code yet.

In reply to Re^5: Is there something faster than string concatenation? (hermit crabs) by eyepopslikeamosquito
in thread Is there something faster than string concatenation? by rdj

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