We are running Magento 18.104.22.168 with Lesti_Fpc on an adequately sized managed server. Initially, we used the default file cache, which was fine. But after the catalog grew (although I think ~8000 products is not too bad) and crawlers became more aggressive, the site became slow as soon as the cache was getting a bit bigger. When the cache was cleared, everything was running quick again.
We tried to switch to APC as a cache backend via the following entry in the local.xml:
<global> <cache> <backend>apc</backend> <prefix>MYSHOP_</prefix> </cache> </global>
But this made the problems even worse. I then read that Cm_Cache_Backend_File is made for this problem and integrated it via:
<global> <cache> <backend>Cm_Cache_Backend_File</backend> </cache> </global>
This feels a bit better, but the problem is still the same. To keep the cache small and tidy, I also integrated Aoe_CacheCleaner, but this also does not help. Still, as soon as the cache is cleared, everything is running quick again.
Based on the answer by infabo, I also activated
Cm_Cache_Backend_File for the FPC with the file
app/etc/fpc.xml and the following content:
<?xml version="1.0"?> <config> <global> <fpc> <lifetime>86400</lifetime> <backend>Cm_Cache_Backend_File</backend> </fpc> </global> </config>
I am sure this makes sense, but it also does not solve the problem.
I know that the general solution to this problem seems to be Redis (or maybe alternatively Memcached) as a cache backend, but unfortunately, it is not available on our managed server. Switching to another hosting company is not (yet) an option.
I investigated a lot now, but I do not have any more idea. Maybe anyone else can help?