Perl: string length limitations in real life

Question

While, for example, perldata documents that scalar strings in Perl are limited only by available memory, I'm strongly suspecting in real life there would be some other limits.

I'm considering the following ideas:

• I'm not sure how strings are implemented in Perl — is there some sort of byte/character counter? If there is, then probably it's implemented as a platform-dependent integer (i.e. 32-bit or 64-bit), so effectively it would limit strings to something like 2 ** 31, 2 ** 32, 2 ** 63 or 2 ** 64 bytes.
• If Perl doesn't use a counter and instead uses some byte to terminate the string (which would be strange, as it's perfectly ok to have a string like "foo\0bar" in Perl), then all operations would inevitably get much slower as string length increases.
• Most string functions that Perl deals with strings, such as length, for example, return normal scalar integer, and I strongly suspect that it would be platform-limited integer too.

So, what would be the other factors that limit Perl string length in real life? What should be considered an okay string length for practical purposes?

Answer 1

It keep track of the size of the buffer and the number of bytes therein.

$ perl -MDevel::Peek -e'$x="abcdefghij"; Dump($x);'
SV = PV(0x9222b00) at 0x9222678
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x9238220 "abcdefghij"\0
  CUR = 10                        <-- 10 bytes used
  LEN = 12                        <-- 12 bytes allocated

• On a 32-bit build of Perl, it uses 32-bit unsigned integer for these values. This is (exactly) large enough to create a string that uses up your process's entire 4 GiB address space.

• On a 64-bit build of Perl, it uses 64-bit unsigned integer for those values. This is (exactly) large enough to create a string that uses up your process's entire 16 EiB address space.

The docs are correct. The size of the string is limited only by available memory.