Performance is worse in 3.0

Performance is generally turning out to be worse after 8099, despite a number of unrelated performance enhancements being delivered. This isn't entirely unexpected, given a great deal of time was spent optimising the old code, however things appear worse than we had hoped.

My expectation was that workloads making extensive use of CQL constructs would be faster post-8099, however the latest tests performed with very large CQL rows, including use of collections, still exhibit performance below that of 2.1 and 2.2.

Eventually, as the dataset size grows large enough and the locality of access is just right, the reduction in size of our dataset will yield a window during which some users will perform better due simply to improved page cache hit rates. We seem to see this in some of the tests. However we should be at least as fast (and really faster) off the bat.

The following are some large partition benchmark results, with as many as 40K rows per partition, running LCS. There are a number of parameters we can modify to see how behaviour changes and under what scenarios we might still be faster, but the picture painted isn't brilliant, and is consistent, so we should really try and figure out what's up before GA.

trades-with-flags (collections), blade11b
trades-with-flags (collections), blade11
trades (no collections), blade11

Sylvain Lebresne: will you have time to look into this before GA?