[drupal-devel] Drupal cache statistics

Nicholas Ivy nji at njivy.org
Thu Jun 2 14:30:01 UTC 2005

On Jun 2, 2005, at 1:36 AM, Dries Buytaert wrote:

> On 01 Jun 2005, at 18:32, Nicholas Ivy wrote:
>> 2. Page elements poll the cache for every page request.  When a page 
>> is loaded, the page element computes a cache key and checks for 
>> cached results.  For example, in nodelist.module I used an 
>> md5-checksum of the sql query as a cache key.  If the sql query 
>> changes, the cache misses.  In this case, the challenge is to 
>> efficiently compute accurate cache keys and handle stale results, but 
>> at least we don't have to worry about every event in the system.
> Do you suggest we render the page, compute and md5-sum on the 
> generated HTML, drop the generated page on the floor, and serve the 
> page from the cache?  Or do you suggest computing the md5-sum on 
> something else?  I don't understand how that could work ...

No, I am not suggesting that we render pages and throw away the 
results.  I am suggesting we compute the cache key using something 
else, something that will have to be identified per page element.  Near 
the top of a block of code, we could use input values as cache keys to 
see if we have done this work already.  If so, we skip the rest of the 
block and return the cache.

I see a couple problems with this scheme, however.
1. We need to identify the important inputs that characterize the 
2. We need to check early enough in the code for a cached result in 
order for the work to be worthwhile.

As for nodelist.module, I looked again at how db_rewrite_sql() works 
and realized I got it wrong -- the structure of the query doesn't 
change per user.  I thought I had an input to the page that completely 
characterized the result, but I really don't.  So I'll have to work on 


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