Recently, one of our clients started having issues saving products, where it would take almost a full minute between saves. They had not installed any plugins recently, nor have they increased their product counts. The problem just started “happening”.
We ruled out the index process, database degradation, network, firewall, etc. Everything we could think of.
On a whim, we checked the database tables themselves and noticed that the “core_cache_tag” had reached nearly 1.3 GB in size. This had happened before, but had never caused any issues in saving products.
Based on our research ( Thanks Sonassi!), we found that the core_cache_tag grows exponentially on its own without truncating!
After truncating that table, the saves on products and refreshing caches, went back to taking a second rather than a minute. Magento REALLY needs to fix this.
Until then, keep an eye on the table and if it grows out of control, you will need to truncate it.