Yum has error on primary.xml.gz or similar when behind squid. (clearing and reloading a URL in Squid)
Verify the entry is getting hit in your cache by watching your logs
TCP_MEM_HIT/200 1597 GET http://linuxdownload.adobe.com/linux/x86_64/repodata/primary.xml.gz – HIER_NONE/- application/x-gzip (or similar)
To reload this entry run
squidclient -r http://linuxdownload.adobe.com/linux/x86_64/repodata/primary.xml.gz
OR
To clear this entry
squidclient -m PURGE http://linuxdownload.adobe.com/linux/x86_64/repodata/primary.xml.gz
You can also whitelist this in several ways if you do not want this to be cached or do not want it cached for long (ie 24 hours) but I will save that for another post.
Caching packages and yum related information in squid can be helpful if you have a large number of machines behind a company/personal proxy and have limited (either in speed or monthly amounts) bandwidth at your location. While running a local mirror is preferred for many reasons this could fill that role till such time as you feel you need the complexity of local mirror.