Changes between Version 3 and Version 4 of TracDev/Proposals/CacheInvalidation

Timestamp:

Mar 6, 2009, 9:21:38 PM (15 years ago)

Author:

Christian Boos

Comment:

some comments about both ideas

TracDev/Proposals/CacheInvalidation

@@ -74 +74 @@
 Only the code changes for trac/env.py and trac/wiki/interwiki.py are roughly implemented (i.e. not tested yet - just to illustrate the above).
 
-See attachment:cache_control-r7933.diff
+See attachment:cache_control-r7933.diff.
+For testing, manual creation of a cache_control table is needed:
+{{{
+CREATE TABLE cache_control( key text primary key, generation int);
+}}}
+
+The method names and API has a bit evolved, now I have:
+ - `env.update_cache_control()`, called in `open_environment`
+ - `env.invalidate_cache(key)`, called by the Component in place of `config.touch()`
+ - `env.is_cache_valid(key)`, called by the Component when checking for cache validity
+ - `env.validate_cache(key)` once the cache has been updated
+
+That concludes my initial approach to the problem. Now let's take into account what was proposed in idea 1...
+
+=== Discussion ===
+While the two approaches are quite close in spirit, there are a few differences.
+
+I initially thought that having the cache control managed at the level of the environment was more natural than having a specialized Component (it's a "service" offered by the environment to all its Components, like providing them with a db connection).
+
+But I see your point in having the cache logic handled "once for all", without the need to re-implement it in various places. If that's doable in a not too complicated way, it may be worth doing it.
+
+I've not yet added time-based invalidation, but if really needed, that can be added as well.
+
+The open problem I see as well is about maintaining a coherent view from the cache during the lifetime of a given request. That might indeed be another argument in favor of a dedicated component with a more advanced cache logic. Anyway, the patch above is at least a first step that seems to work fine in my testing.