stale=false range scan workload timing out.

a degradation in stale=false scan performance with run duration of the test is seen.

run with default WAL size:

with default WAL size, scan timeouts start occuring 90 minutes into the test
logs:
https://s3.amazonaws.com/cb-customers/performance/15785/collectinfo-2015-07-26T074724-ns_1%40172.23.100.16.zip

run with 10x WAL size:
with 10x WAL size, scan timeouts start occuring 180 minutes into the test. 10x WAL size provides better write throughput during compaction without increasing catch-up time of compaction process.
logs:
https://s3.amazonaws.com/cb-customers/performance/15785/collectinfo-2015-07-27T035451-ns_1%40172.23.100.16.zip

example timeout error from client:
2015-07-26T20:03:10.193Z-07:00 [Error] [GsiScanClient:"172.23.100.16:9101"] connection "172.23.100.56:41752" response transport failed `read tcp 172.23.100.16:9101: i/o timeout`