Greg Stein wrote:
On Sun, Nov 04, 2001 at 03:00:43PM -0800, Brian Pane wrote:
... 2. Change the performance-sensitive fields in the httpd's request_rec from apr_table_t (like r->headers_in) to some different data type (e.g., "ap_http_headers_t") that supports O(log(n)) or O(1) get/set operations Pros: * Performance improvement for the httpd * Other code that uses apr_table_t isn't affected Cons: * Lots of changes required to the httpd core and all modules
This is the most optimal approach. You can build a structure that is O(1) for the common headers (by using tokens for the headers rather than strings). Other headers can also be heavily optimized through a hash lookup. I think this custom type would be a wrapper around an apr_hash_t.
This would work well in combination with an enhancement to apr_hash_t. The big problem with apr_hash_t is that it's inefficient when the keys are case-insensitive strings. Currently, the caller has to make a copy of the key, normalize it to all-lowercase or all-caps, and then call apr_hash_(get|set). This defeats some of the performance benefits of using a hash table.
IMHO, hash tables with case-insensitive string keys are an important enough special case to justify custom code within apr_hash_t. E.g.,
apr_hash_t *apr_hash_make_case_insensitive(apr_pool_t *p); /* works the same as apr_hash_make, except that it sets a flag inside * the resulting hash table that tells the apr_hash_get functions to * use a case-insensitive hash function and strncasecmp instead of * memcmp */
There are some places in the current Apache 2.0 code where this would let us optimize away some "strdup+tolower" operations; filter registration is one good example.
--Brian
