Hello everyone,
I was wondering if it would make sense to store small strings (length <= 7)
directly inside the zval struct, thereby avoiding the need to extra allocate a
zend_string, which would also not entail any costly indirection and refcounting
for such strings.
The idea would be to add a new sruct ``struct { uint8_t len; char val[7]; }
sval`` to the _zend_value union type in order to embed it directly into the
zval struct and use a type flag (zval.u1.v.type_flags) such as IS_SMALL_STRING
to destinguish between a regular heap allocated zend_string and the directly
embedded compact representation.
Small strings are quite common IMHO. In fact quickly sampling my company's PHP
code base I found well over 50% of the strings to be of length <= 7. It would
save a lot of memory allocations as well as pointer indirection, and could also
bypass refcounting logic. Also, comparing small strings for equality would
become a trivial operation (just comparing two pre-aligned 64bit integers) - no
more need to keep small strings interned.
Of course it wouldn't longer be possible to also persistently store the hash
value of a small string, though calculating the hash value for small strings is
less costly anyways because less characters equals less iterations, so that
might not be an issue in practice.
I don't see such an idea in https://wiki.php.net/php-7.1-ideas and I was
wondering: Has anybody experimented with that approach yet? Is it worth
discussing?
Please let me know your thoughts,
Ben
--
Bejamin Coutu
ben.co...@zeyos.com
ZeyOS, Inc.
http://www.zeyos.com
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