On Sun, 7 Feb 2010, Jakub Narebski wrote:
> There is new version of this series in gitweb/cache-kernel-v2 in my
> git/jnareb-git.git fork (clone) of git.git repository at repo.or.cz.
> Now all commits have proper description (for first series one had to
> read comment section in emails for commit description), [...]
Below there are commit messages for gitweb/cache-kernel-v2 branch after
rebase and fixups:
commit 560e2ab10d0f8457fbeca7a26814ff3e32396f7b
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 11:27:22 2010 +0100
gitweb: href(..., -path_info => 0|1)
If named boolean option -path_info is passed to href() subroutine, use
its value to decide whether to generate path_info URL form. If this
option is not passed, href() queries 'pathinfo' feature to check
whether to generate path_info URL (if generating path_info link is
possible at all).
href(-replay=>1, -path_info=>0) is meant to be used to generate a key
for caching gitweb output; alternate solution would be to use freeze()
from Storable (core module) on %input_params hash (or its reference),
e.g.:
$key = freeze \%input_params;
or other serialization technique.
While at it document extra options/flags to href().
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/gitweb.perl | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
commit dd6e8dc27d5b799bd2a1aed03738195dfe3bc5e7
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:13:06 2010 +0100
gitweb/cache.pm - Very simple file based caching
This is first step towards implementing file based output (response)
caching layer that is used on such large sites as kernel.org.
This patch introduces GitwebCaching::SimpleFileCache package, which
follows Cache::Cache / CHI interface, although do not implement it
fully. The intent of following established convention is to be able
in the future to replace our simple file based cache e.g. by one using
memcached.
Like in original patch by John 'Warthog9' Hawley (J.H.) (the one this
commit intends to be incremental step to), the data is stored in the
case as-is, without adding metadata (like expiration date), and
without serialization (which means only scalar data).
To be implemented (from original patch by J.H.):
* cache expiration (based on file stats, current time and global
expiration time); currently elements in cache do not expire
* actually using this cache in gitweb, except error pages
* adaptive cache expiration, based on average system load
* optional locking interface, where only one process can update cache
(using flock)
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Possible extensions (beyond what was in original patch):
* (optionally) show information about cache utilization
* AJAX (JavaScript-based) progress indicator
* JavaScript code to update relative dates in cached output
* make cache size-aware (try to not exceed specified maximum size)
* utilize X-Sendfile header (or equivalent) to show cached data
(optional, as it makes sense only if web server supports sendfile
feature and have it enabled)
* variable expiration feature from CHI, allowing items to expire a bit
earlier than the stated expiration time to prevent cache miss
stampedes (although locking, if available, should take care of
this).
The code of GitwebCaching::SimpleFileCache package in gitweb/cache.pm
was heavily based on file-based cache in Cache::Cache package, i.e.
on Cache::FileCache, Cache::FileBackend and Cache::BaseCache, and on
file-based cache in CHI, i.e. on CHI::Driver::File and CHI::Driver
(including implementing atomic write, something that original patch
lacks).
This patch does not yet enable output caching in gitweb (it doesn't
have all required features yet); on the other hand it includes tests,
currently testing only cache Perl API.
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 269 +++++++++++++++++++++++++++++++++++++++
t/t9503-gitweb-caching.sh | 32 +++++
t/t9503/test_cache_interface.pl | 84 ++++++++++++
t/test-lib.sh | 3 +
4 files changed, 388 insertions(+), 0 deletions(-)
create mode 100644 gitweb/cache.pm
create mode 100755 t/t9503-gitweb-caching.sh
create mode 100755 t/t9503/test_cache_interface.pl
commit 3914e7da792fec50fcc64c0e644d54cf4451703a
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:13:17 2010 +0100
gitweb/cache.pm - Stat-based cache expiration
Add stat-based cache expiration to file-based GitwebCache::SimpleFileCache.
Contrary to the way other caching interfaces such as Cache::Cache and CHI
do it, the time cache element expires in is _global_ value associated with
cache instance, and is not local property of cache entry. (Currently cache
entry does not store any metadata associated with entry... which means that
there is no need for serialization / marshalling / freezing and thawing.)
Default expire time is -1, which means never expire.
To check if cache entry is expired, GitwebCache::SimpleFileCache compares
difference between mtime (last modify time) of a cache file and current time
with (global) time to expire. It is done using CHI-compatible is_valid()
method.
Add some tests checking that expiring works correctly (on the level of API).
To be implemented (from original patch by J.H.):
* actually using this cache in gitweb, except error pages
* adaptive cache expiration, based on average system load
* optional locking interface, where only one process can update cache
(using flock)
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 34 ++++++++++++++++++++++++++++++++--
t/t9503/test_cache_interface.pl | 10 ++++++++++
2 files changed, 42 insertions(+), 2 deletions(-)
commit a55625cb0f2d6c08a28e774fd2ddb4e5347a24b3
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:13:27 2010 +0100
gitweb: Use Cache::Cache compatible (get, set) output caching
This commit actually adds output caching to gitweb, as we have now
minimal features required for it in GitwebCache::SimpleFileCache
(a 'dumb' but fast file-based cache engine). To enable cache you need
at least set $caching_enabled to true in gitweb config, and copy cache.pm
from gitweb/ alongside gitweb.cgi - this is described in more detail
in the new "Gitweb caching" section in gitweb/README
Currently cache support related subroutines in cache.pm (which are
outside GitwebCache::SimpleFileCache package) are not well separated
from gitweb script itself; cache.pm lacks encapsulation. cache.pm
assumes that there are href() subroutine and %actions variable, and
that there exist $actions{$action} (where $action is parameter passed
to cache_fetch), and it is a code reference (see also comments in
t/t9503/test_cache_interface.pl). This is remaining artifact from the
original patch by J.H. (which also had cache_fetch() subroutine).
Gitweb itself uses directly only cache_fetch, to get page from cache
or to generate page and save it to cache, and cache_stop, to be used
in die_error subroutine, as currently error pages are not cached.
The cache_fetch subroutine captures output (from STDOUT only, as
STDERR is usually logged) using either ->push_layer()/->pop_layer()
from PerlIO::Util submodule (if it is available), or by setting and
restoring *STDOUT. Note that only the former could be tested reliably
to be reliable in t9503 test!
Enabling caching causes the following additional changes to gitweb
output:
* Disables content-type negotiation (choosing between 'text/html'
mimetype and 'application/xhtml+xml') when caching, as there is no
content-type negotiation done when retrieving page from cache.
Use 'text/html' mimetype that can be used by all browsers.
* Disable timing info (how much time it took to generate original
page, and how many git commands it took), and in its place show when
page was originally generated (in GMT / UTC timezone).
Add basic tests of caching support to t9500-gitweb-standalone-no-errors
test: set $caching_enabled to true and check for errors for first time
run (generating cache) and second time run (retrieving from cache) for a
single view - summary view for a project.
If PerlIO::Util is available (see comments), test that cache_fetch
behaves correctly, namely that it saves and restores action output in
cache, and that it prints generated output or cached output.
To be implemented (from original patch by J.H.):
* adaptive cache expiration, based on average system load
* optional locking interface, where only one process can update cache
(using flock)
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/README | 70 ++++++++++++++++++++++
gitweb/cache.pm | 78 ++++++++++++++++++++++++
gitweb/gitweb.perl | 102 ++++++++++++++++++++++++++++----
t/gitweb-lib.sh | 2 +
t/t9500-gitweb-standalone-no-errors.sh | 19 ++++++
t/t9503/test_cache_interface.pl | 93 +++++++++++++++++++++++++++++
6 files changed, 352 insertions(+), 12 deletions(-)
commit 3e471ebd31e881ce1439f23075378c2ec6b95e4d
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:13:31 2010 +0100
gitweb/cache.pm - Adaptive cache expiration time
Add to GitwebCache::SimpleFileCache support for adaptive lifetime
(cache expiration) control. Cache lifetime can be increased or
decreased by any factor, e.g. load average, through the definition
of the 'check_load' callback.
Note that using ->set_expires_in, or unsetting 'check_load' via
->set_check_load(undef) turns off adaptive caching.
Make gitweb automatically adjust cache lifetime by load, using
get_loadavg() function. Define and describe default parameters for
dynamic (adaptive) cache expiration time control.
There are some very basic tests of dynamic expiration time in t9503,
namely checking if dynamic expire time is within given upper and lower
bounds.
To be implemented (from original patch by J.H.):
* optional locking interface, where only one process can update cache
(using flock)
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 55 +++++++++++++++++++++++++++++++++++---
gitweb/gitweb.perl | 27 +++++++++++++++++-
t/t9503/test_cache_interface.pl | 22 +++++++++++++++
3 files changed, 97 insertions(+), 7 deletions(-)
commit 984390f99c33d82cd4ddbfa6e00c721d9e74cddb
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:13:52 2010 +0100
gitweb: Use CHI compatible (compute method) caching
If $cache provides CHI compatible ->compute($key, $code) method, use it
instead of Cache::Cache compatible ->get($key) and ->set($key, $data).
While at it, refactor regenerating cache into cache_calculate subroutine.
GitwebCache::SimpleFileCache provides 'compute' method, which currently
simply use 'get' and 'set' methods in proscribed manner. Nevertheless
'compute' method can be more flexible in choosing when to refresh cache,
and which process is to refresh/(re)generate cache entry. This method
would use (advisory) locking to prevent 'cache miss stampede' (aka
'stampeding herd') problem in the next commit.
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 39 ++++++++++++++++++++++++++++++++++++---
1 files changed, 36 insertions(+), 3 deletions(-)
commit 7d0109e4379f5187364edf7c25cdbc5247609f64
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:18:14 2010 +0100
gitweb/cache.pm - Use locking to avoid 'cache miss stampede' problem
In the ->compute($key, $code) method from GitwebCache::SimpleFileCache,
use locking (via flock) to ensure that only one process would generate
data to update/fill-in cache; the rest would wait for the cache to
be (re)generated and would read data from cache.
Currently this feature can not be disabled (via %cache_options).
A test in t9503 shows that in the case where there are two clients
trying to simultaneously access non-existent or stale cache entry,
(and generating data takes (artifically) a bit of time), if they are
using ->compute method the data is (re)generated once, as opposed to
if those clients are just using ->get/->set methods.
To be implemented (from original patch by J.H.):
* background building, and showing stale cache
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 29 ++++++++++++++++-
t/t9503/test_cache_interface.pl | 65 +++++++++++++++++++++++++++++++++++++++
2 files changed, 92 insertions(+), 2 deletions(-)
commit e7985f69eb9000860b155939d5fd7040e30f682f
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:19:21 2010 +0100
gitweb/cache.pm - Serve stale data when waiting for filling cache
When process fails to acquire exclusive (writers) lock, then instead
of waiting for the other process to (re)generate and fill cache, serve
stale (expired) data from cache. This is of course possible only if
there is some stale data in cache for given key.
This feature of GitwebCache::SimpleFileCache is used only for an
->update($key, $code) method. It is controlled by 'max_lifetime'
cache parameter; you can set it to -1 to always serve stale data
if it exists, and you can set it to 0 (or any value smaller than
'expires_min') to turn this feature off.
This feature, as it is implemented currently, makes ->update() method a
bit assymetric with respect to process that acquired writers lock and
those processes that didn't, which can be seen in the new test in t9503.
The process that is to regenerate (refresh) data in cache must wait for
the data to be generated in full before showing anything to client, while
the other processes show stale (expired) data immediately. In order to
remove or reduce this assymetry gitweb would need to employ one of the two
alternate solutions. Either data should be (re)generated in background,
so that process that acquired writers lock would generate data in
background while serving stale data, or alternatively the process that
generates data should pass output to original STDOUT while capturing it
("tee" otput).
When developing this feature, ->is_valid() method acquired additional
extra optional parameter, where one cap pass expire time instead of using
cache-wode global expire time.
To be implemented (from original patch by J.H.):
* background building,
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 23 ++++++++++----
gitweb/gitweb.perl | 8 +++++
t/t9503/test_cache_interface.pl | 63 +++++++++++++++++++++++++++++++++++++-
3 files changed, 86 insertions(+), 8 deletions(-)
commit 19911970b8a811a6382e39a10b071bff1dd4bd70
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:20:46 2010 +0100
gitweb/cache.pm - Regenerate (refresh) cache in background
This commit removes assymetry in serving stale data (if it exists)
when regenerating cache in GitwebCache::SimpleFileCache. The process
that acquired exclusive (writers) lock, and is therefore selected to
be the one that (re)generates data to fill the cache, can now generate
data in background, while serving stale data.
This feature can be enabled or disabled on demand via 'background_cache'
cache parameter. It is turned on by default.
To be implemented (from original patch by J.H.):
* server-side progress indicator when waiting for filling cache,
which in turn requires separating situations (like snapshots and
other non-HTML responses) where we should not show 'please wait'
message
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 36 +++++++++++++++++++++++++++++-------
gitweb/gitweb.perl | 9 +++++++++
t/t9503/test_cache_interface.pl | 14 ++++++++------
3 files changed, 46 insertions(+), 13 deletions(-)
commit ce97bb5bc1660f6d5c9b9be68c556ac94097978c
Author: Jakub Narebski <jnareb@xxxxxxxxx>
Date: Sun Feb 7 13:21:10 2010 +0100
gitweb: Show appropriate "Generating..." page when regenerating cache
When there exist stale/expired (but not too stale) version of
(re)generated page in cache, gitweb returns stale version (and updates
cache in background, assuming 'background_cache' is set to true value).
When there is no stale version suitable to serve the client, currently
we have to wait for the data to be generated in full before showing it.
Add to GitwebCache::SimpleFileCache, via 'generating_info' callback,
the ability to show user some activity indicator / progress bar, to
show that we are working on generating data.
Gitweb itself uses "Generating..." page as activity indicator, which
redirects (via <meta http-equiv="Refresh" ...>) to refreshed version
of the page after the cache is filled (via trick of not closing page
and therefore not closing connection till data is available in cache,
checked by getting shared/readers lock on lockfile for cache entry).
The git_generating_data_html() subroutine, which is used by gitweb
to implement this feature, is highly configurable: you can choose
initial delay, frequency of writing some data so that connection
won't get closed, and maximum time to wait for data in "Generating..."
page (see %generating_options hash).
Currently git_generating_data_html() contains hardcoded "whitelist" of
actions for which such HTML "Generating..." page makes sense.
This implements final feature from the original gitweb output caching
patch by J.H.
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
gitweb/cache.pm | 23 +++++-
gitweb/gitweb.perl | 154 ++++++++++++++++++++++++++++++++++++++-
t/t9503/test_cache_interface.pl | 45 +++++++++++
3 files changed, 216 insertions(+), 6 deletions(-)
--
Jakub Narebski
Poland
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