Thread Starter
sqlwiz
(@sqlwiz)
I see that if /tmp/pgcache is removed, the plugin does not recreate it or the .htacces file. We will have to manage that. This deployment is a multi-server environment, I’d expect that a page may wind up cached on each server, but I don’t see that as a problem for a page cache.
Frederick – what do you think about that?
I have to give this some thought, checking for changes on the file system requires invoking PHP constantly.
Thread Starter
sqlwiz
(@sqlwiz)
If you that you might manage the /tmp directory, I did not expect that from w3tc. This is a special case in which we cannot write to the file system.
My question concerns disk based enhanced page caching in a multiple server setup. It seems that on any given server, if Apache does not find a given cached file, it will send the request to WP and the result will be cached. So I think the down side is that a given page could be different on the various servers for a period of time if posts are updated. We would probably keep the cache time short and flush as needed.
Generating cache files on respective servers is not really an optimal performance win, coupled with the fact that there are opportunities for dirty reads (poor user experience) etc. So that’s why network file servers (NFS) are typically introduced into multiple server situations. But this introduces even more issues with multiple server than it would seem.
Evidently other popular caching solutions are finally realizing the same. To ensure optimal functionality and full kernel performance, functionality outside the scope of the plugin is required. For multiple server configurations, install memcache pecl extension and memcached. Otherwise you’ll find even more anomalies than you have thus far depending on your server configuration.
Thread Starter
sqlwiz
(@sqlwiz)
We’re using memcached for the database. I was trying to get the big win from bypassing php and wp. I’ll stick with memcached for the pgcache.
Depending on your traffic level, you may be OK with disk. On many sites my time to first byte doesn’t really suffer even when using memcache + memcached. However in terms of ideal scenarios, giving apache a local .html file is best. Cache files on a NFS do not benefit from the kernel optimizations that make the local file system such a big win in the memory vs. disk debates.
