| Lars Hjemli | 25105d7 | 2006-12-10 22:31:36 +0100 | [diff] [blame] | 1 | Cache algorithm |
| 2 | =============== |
| 3 | |
| 4 | Cgit normally returns cached pages when invoked. If there is no cache file, or |
| 5 | the cache file has expired, it is regenerated. Finally, the cache file is |
| 6 | printed on stdout. |
| 7 | |
| 8 | When it is decided that a cache file needs to be regenerated, an attempt is |
| 9 | made to create a corresponding lockfile. If this fails, the process gives up |
| 10 | and uses the expired cache file instead. |
| 11 | |
| 12 | When there is no cache file for a request, an attempt is made to create a |
| 13 | corresponding lockfile. If this fails, the process calls sched_yield(2) before |
| 14 | restarting the request handling. |
| 15 | |
| 16 | In pseudocode: |
| 17 | |
| 18 | name = generate_cache_name(request); |
| 19 | top: |
| 20 | if (!exists(name)) { |
| 21 | if (lock_cache(name)) { |
| 22 | generate_cache(request, name); |
| 23 | unlock_cache(name); |
| 24 | } else { |
| 25 | sched_yield(); |
| 26 | goto top; |
| 27 | } |
| 28 | } else if (expired(name)) { |
| 29 | if (lock_cache(name)) { |
| 30 | generate_cache(request, name); |
| 31 | unlock_cache(name); |
| 32 | } |
| 33 | } |
| 34 | print_file(name); |
| 35 | |
| 36 | |
| 37 | The following options can be set in /etc/cgitrc to control cache behaviour: |
| 38 | cache-root: root directory for cache files |
| 39 | cache-root-ttl: TTL for the repo listing page |
| 40 | cache-repo-ttl: TTL for any repos summary page |
| 41 | cache-dynamic-ttl: TTL for pages with symbolic references (not SHA1) |
| 42 | cache-static-ttl: TTL for pages with sha1 references |
| 43 | |
| 44 | TTL is specified in minutes, -1 meaning "infinite caching". |
| 45 | |
| 46 | |
| 47 | Naming of cache files |
| 48 | --------------------- |
| 49 | Repository listing: <cachedir>/index.html |
| 50 | Repository summary: <cachedir>/<repo>/index.html |
| 51 | Repository subpage: <cachedir>/<repo>/<page>/<querystring>.html |
| 52 | |
| 53 | The corresponding lock files have a ".lock" suffix. |
| 54 | |