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| -rw-r--r-- | README | 54 |
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@@ -0,0 +1,54 @@ +Cache algorithm +=============== + +Cgit normally returns cached pages when invoked. If there is no cache file, or +the cache file has expired, it is regenerated. Finally, the cache file is +printed on stdout. + +When it is decided that a cache file needs to be regenerated, an attempt is +made to create a corresponding lockfile. If this fails, the process gives up +and uses the expired cache file instead. + +When there is no cache file for a request, an attempt is made to create a +corresponding lockfile. If this fails, the process calls sched_yield(2) before +restarting the request handling. + +In pseudocode: + + name = generate_cache_name(request); +top: + if (!exists(name)) { + if (lock_cache(name)) { + generate_cache(request, name); + unlock_cache(name); + } else { + sched_yield(); + goto top; + } + } else if (expired(name)) { + if (lock_cache(name)) { + generate_cache(request, name); + unlock_cache(name); + } + } + print_file(name); + + +The following options can be set in /etc/cgitrc to control cache behaviour: + cache-root: root directory for cache files + cache-root-ttl: TTL for the repo listing page + cache-repo-ttl: TTL for any repos summary page + cache-dynamic-ttl: TTL for pages with symbolic references (not SHA1) + cache-static-ttl: TTL for pages with sha1 references + +TTL is specified in minutes, -1 meaning "infinite caching". + + +Naming of cache files +--------------------- +Repository listing: <cachedir>/index.html +Repository summary: <cachedir>/<repo>/index.html +Repository subpage: <cachedir>/<repo>/<page>/<querystring>.html + +The corresponding lock files have a ".lock" suffix. + |