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Remove implementation details from README

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Let README describe the "bigger picture" instead.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
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Lars Hjemli 2006-12-13 02:06:29 +01:00
parent 9c2e863ec2
commit dcef257d4f
1 changed files with 27 additions and 46 deletions
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README
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@ -1,54 +1,35 @@
Cache algorithm
===============
Cgit normally returns cached pages when invoked. If there is no cache file, or cgit - cgi for git
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: This is an attempt to create a fast web interface for the git scm, using a
cache-root: root directory for cache files frontside cache to decrease server io-pressure.
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". When cgit is invoked, it looks for a cached page matching the request. If no
such cachefile exist (or it has expired), it is (re)generated. Finally, the
cachefile is returned to the client.
If the cachefile has expired, but cgit is unable to lock the cachefile, the
client will get the stale cachefile after all. This is done to favour page
throughput over page freshness.
Naming of cache files Also, when a cachefile is generated, a few cache-related http-headers are
--------------------- created: "Modified" is set to current time(2), while "Expires" is set to
Repository listing: <cachedir>/index.html time(2) + <cachefile TTL> * 60 (unless the TTL is negative, in which case it
Repository summary: <cachedir>/<repo>/index.html is read as "60 * 60 * 24 * 365"). This is done to avoid repeated requests for
Repository subpage: <cachedir>/<repo>/<page>/<querystring>.html already visited pages.
The corresponding lock files have a ".lock" suffix. The following cache-related options can be set in /etc/cgitrc:
cache-root=<path> root directory for cache files
cache-root-ttl=<min> TTL for the repo listing page
cache-repo-ttl=<min> TTL for repo summary pages
cache-dynamic-ttl=<min> TTL for pages with symbolic references
cache-static-ttl=<min> TTL for pages with sha1 references
The cachefiles are split into different directories, based on the requested
repository and page:
Repo listing: <cachedir>/index.html
Repo summary: <cachedir>/<repo>/index.html
Repo subpage: <cachedir>/<repo>/<page>/<querystring>.html