I have been working with Zimbra Support on this issue, but haven't dug up the root cause yet. I wanted to throw this out to the list to see if any of you may have experienced this or have some suggestions on what we might look at / settings to tweak.
We just upgraded from ZCS 6.0.14 NE to 7.2.0. The Monday after the upgrade users started reporting seeing "Server Slow to Respond" warnings (higher percentage of these were IE users). With a little looking around we found that our ldap replica server's cpu load had increased dramatically post-upgrade. Pre-upgrade we ran less than 1 (when checking "top"). Post-upgrade, we would run 5-7 with spikes up to 10 and 11. We created a Gal Sync account on the mailstores and that helped a little. We tweaked a couple other settings and those helped a minor amount also. We now run 3-4 with spikes up to 7-9 about once or twice a day during the heavy usage times. We have 8 cpus and 16 GB of RAM on the ldap replica server, so even with these loads, we wouldn't really expect users to be receiving slow server notices. We are running Red Hat 5, 64 bit. We have approximately 30,000 accounts, but closer to 2,000 moderate to heavy users. All our other servers show very low loads, including the master ldap server. All the slapd process threads are running 200-400% cpu (again in the top, cpu% column) most of the time.
We have gone through the Zimbra Large Deployment Performance Guide and made sure we followed the settings advice there as best we could. We installed Patch 1 for ZCS 7.2.0 and that didn't resolve this issue.
Any ideas or suggestions? Any info I left out that would be useful?
Thanks,
Tim Ross
Application Administrator
Enterprise Applications Group
Cal Poly State University, San Luis Obispo