Summary:
**Summary**:
Set defaults for high-pri and low-pri thread pools in regression test script.
**Reason for this change**:
With #2680 , high-pri and low-pri thread pools get different numbers than before if `num_high_pri_threads` and `num_low_pri_threads` options are not explicitly passed to db_bench in regression test script ... leading to a false-positive regression.
**Test Plan**:
REMOTE_HOST=udb1671.prn3 TEST_MODE=1 FBSOURCE=~/fbsource ~/fbsource/fbcode/rocks/tools/debug_regression_test.sh viewstate (with very minor changes to the internals).
Observe P50 and P99 which showed up as regressions in our graphs.
Stats with the commit prior to #2680 , ie. 4f81ab3 :
seekrandomwhilewriting : 75.096 micros/op 13316 ops/sec; 168.6 MB/s (7499074 of 7500000 found)
Microseconds per seek:
Count: 120000000 Average: 1197.7254 StdDev: 33.35
Min: 187 Median: 980.5292 Max: 1816424
Percentiles: **P50: 980.53** P75: 1494.57 **P99: 4185.64** P99.9: 7800.11 P99.99: 15039.64
Stats at #2680, ie. at commit dce6d5a (false-positive regression):
seekrandomwhilewriting : 85.330 micros/op 11719 ops/sec; 148.4 MB/s (7499073 of 7500000 found)
Microseconds per seek:
Count: 120000000 Average: 1362.3261 StdDev: 27.86
Min: 185 Median: 1088.1915 Max: 652760
Percentiles: **P50: 1088.19** P75: 1658.12 **P99: 5361.15** P99.9: 7997.95 P99.99: 11730.07
Stats with the current change on top of dce6d5a :
seekrandomwhilewriting : 77.780 micros/op 12856 ops/sec; 162.8 MB/s (7499102 of 7500000 found)
Microseconds per seek:
Count: 120000000 Average: 1226.6744 StdDev: 17.16
Min: 185 Median: 994.2956 Max: 2553530
Percentiles: **P50: 994.30** P75: 1513.68 **P99: 4284.30** P99.9: 9338.64 P99.99: 23008.86
Closes https://github.com/facebook/rocksdb/pull/2801
Differential Revision: D5742338
Pulled By: sagar0
fbshipit-source-id: cc5d727c1a131f2a7070d1bb892efbe929b976ff
06b37eef7b