I am in the process of preparing a patch to add a new RewriteMap type and could use some input from all of you on the best implementation. What I am creating is basically a clone of the txt map type, except that each line is a regexp followed by a replacement (with potential back-references).
"You can just do those as RewriteRules...no need for a map," you say. True, except that I am looking at an automated, application-created list, and I don't really want the application to be writing out configuration files or .htaccess files. I would be much more comfortable with the app writing out a map file that has limited functionality and scope. Plus, it would be easy for the app to just create 'regexp replacement' lines at build time. So, I have created a crude, working proof-of-concept of this. It basically copies all of the functionality of the txt maps, including the cache, but in the lookup_map_regexpfile() function, it compiles the regexp for each line, attempts a match, and returns the backref-substituted replacement. (This pair gets cached.) This works beautifully as is, but it is horribly inefficient to have to compile the REs every time we come in with a new key/URL. So, I was thinking of precompiling all of them and see three options: 1. Precompile and store all of the REs at config load time. 2. Compile and store all of the REs the first time we hit lookup_map_regexpfile() or when the map file is updated. 3. Compile and store each RE as we read through the map file in lookup_map_regexpfile() until a match is found and bail (full list will be built over time). #1 is nice, because all of the work is done up front and will be fast from then on. The problem, though, is that I would like this map to reload/refresh if the map file gets changed like the other types do. #2 and #3 solve this. With #2 I worry about performance of compiling everything if the map file gets updated and we get a thundering herd. With #3 there is some coordination to manage with respect to which lines have been compiled and which ones haven't. Does anyone have thoughts as to: 1. When/how should the map REs be compiled/precompiled? One of the options above or something else? 2. Where should the compiled REs be stored: in an existing pool or a new one? Thanks for any input. - Jim
