[development] Refresh rather than re-create D6 cache

Tomáš Fülöpp (vacilando.org) tomi at vacilando.org
Mon Oct 18 13:31:23 UTC 2010

Yes, Larry, I did experiment with that approach as well. It allows caches to
expire at different times, but a) you need to keep some sort of approximate
overview about the various expiration delays you're setting (so that they
don't have much chance happening at the same time) and b) whenever such
cache happens to expire, it still gets deleted at cron and then will have to
be re-calculated during the precious time of page request.

Currently I am thinking about the following approach - crude pseudo code:

// Make sure no other cache has been started over defined period
* set buffer period between cache refreshes $cbuffer = 15 seconds
* if ( (time()-$lastcacherun) > $cbuffer )

// Check if the cache at hand has expired
* Set some cache life time $clife
* SELECT `created` FROM `cache` where `cid` = 'cachedobjectname'
* if ( (time()-$created) > $clife )

// Refresh the expired cache
* $lastcacherun = time()
* recreate cachedobjectname
* DELETE FROM `cache` WHERE cid = 'cachedobjectname'
* cache cachedobjectname using cache_set  with CACHE_PERMANENT

What do you think?

On Mon, Oct 18, 2010 at 14:34, larry at garfieldtech.com <
larry at garfieldtech.com> wrote:

> Just to make sure, have you tried using the minimum cache lifetime on the
> performance page?  It essentially says that a cache record will always last
> at least that long, even if a clear is requested for it. That's your first
> step if you're finding some caches clearing too frequently (especially the
> expensive filter and page caches).
> --Larry Garfield
> On 10/18/10 5:22 AM, Tomáš Fülöpp (vacilando.org) wrote:
>> Hi,
>> In D6, after all caches are cleared, or after a lot of them expire and
>> get emptied by cron, the server load spikes seriously because all such
>> caches need to be re-populated.
>> Since this happens more and more on sites I work on, I have been
>> thinking about using another approach in my modules, in the sense that
>> caches would be /refreshed/ rather than cleared and re-populated. Each
>> cache refresh would run depending on e.g. a simple variable storing last
>> time stamp of any other cache refresh.
>> This would assure that a) all cached values would be available at all
>> times, b) caches would never be re-calculated all at the (near) same time.
>> I am about to write logic for this, but wanted to first check with
>> others in the list -- perhaps some of you know or can point to an
>> elegant solution that already exists.
>> Thanks!
>> vacilando
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