866205 wrote:No, it does not relate more to writes. It affects read operations on data in any dirty page in the DB cache. It actually shows up measurably against read operations in practice, because read responses are generally so much faster that the effect of the checkpoint is significant.
Not sure about db checkpoint interval, as this will relate more on to the write commit time. Not sure how this will impact the search etime.
Filesytem cache is fine, but the cache hit ratio would not take the filesystem cache in to account. But yes the filesystem cache with zfs would improve the performance. Again with version 7 compression of entries can be achieved for better caching, and this will have impact on uncompressing the entries having utilization of cpu going higher.Certainly, when you use filesystem cache, the DS cache management is not as critical. Entry compression has been shown to have a relatively minor cost in CPU and an extremely beneficial effect on I/O. I'd suggest running some performance tests yourself to see what benefit compression offers your deployment.
Cache hit ration would useless only if we dont consider other attributes like the repetitive searches seen in the logs, but my case it is all the time different users who are accessing the db.The server-computed cache hit ratio is useless because it generally tells you next to nothing about what is happening in real time. Once your server has been up for a month or two, the number of cachetries is so huge, your cache performance could completely bottom out for minutes at a time with no visible effect on the hit ratio. All it will tell you is the average hit ratio over the entire uptime of the server. I don't know what you call that, but I call it useless, since I am not all that interested in such a non-specific statistic.
Using all 20M entries to be in cache, we need to have a RAM size of 100G to the entry cache to have all the entries in memory and more including the datastructure that will be stored in the entry cache. As the users who login are not the same all the time.That seems pretty high. Have you verified this empirically?