# Performance improvements - Thread: https://externals.io/message/47560 - Original archive: https://news-web.php.net/php.internals/47560 - Started by Zeev Suraski on 2010-03-24T14:12:17+00:00 - Messages: 1 - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #47560 — Zeev Suraski — 2010-03-24T14:12:17+00:00 URL: https://externals.io/message/47560#47560 Hi, Over the last few weeks we've been working on several ideas we had for performance enhancements. We've managed to make some good progress. Our initial tests show roughly 10% speed improvement on real world apps. On pure OO code we're seeing as much as 25% improvement (!) While this still is a work in progress (and not production quality code yet) we want to get feedback sooner rather than later. The diff (available at http://bit.ly/aDPTmv) applies cleanly to trunk. We'd be happy for people to try it out and send comments. What does it contain? 1) Constant operands have been moved from being embedded within the opcodes into a separate literal table. In additional to the zval it contains pre-calculated hash values for string literals. As result PHP uses less memory and doesn't have to recalculate hash values for constants at run-time. 2) Lazy HashTable buckets allocation – we now only allocate the buckets array when we actually insert data into the hash for the first time. This saves both memory and time as many hash tables do not have any data in them. 3) Interned strings (see http://en.wikipedia.org/wiki/String_interning). Most strings known at compile-time are allocated in a single copy with some additional information (pre-calculated hash value, etc.). We try to make most incarnations of a given string point to that same single version, allowing us to save memory, but more importantly - run comparisons by comparing pointers instead of comparing strings and avoid redundant hash value calculations. A couple of notes: a. Not all of the strings are interned - which means that if a pointer comparison fails, we still go through a string comparison; But if it succeeds - it's good enough. b. We'd need to add support for this in the bytecode caches. We'd be happy to work with the various bytecode cache teams to guide how to implement support so that you do not have to intern on each request. To get a better feel for what interning actually does, consider the following examples: // Lookup for $arr will not calculate a hash value, and will only require a pointer comparison in most cases // Lookup for "foo" in $arr will not calculate a hash value, and will only require a pointer comparison // The string "foo" will not have to be allocated as a key in the Bucket // "blah" when assigned doesn't have to be duplicated $arr[“foo”] = “blah”; $a = “b”; if ($a == “b”) { // pointer comparison only ... } Comments welcome! Zeev Patch available at: http://bit.ly/aDPTmv