Report error when sample space is too low for key generation

It's important that we report an error when the sample space is too
low for the given k/v size and key count. Previously, we'd end up
entering an infinite wait time (essentially an infinite loop); this
has been fixed.

CHANGELOG.md

@@ -4,6 +4,10 @@ All changes in this project will be noted in this file.
 
 ## Unreleased
 
+### Fixes
+
+- Fixed infinite wait (loop) when sample space for key generation is not large enough
+
 ### Additions
 
 - Added support for system native endian storage (backward compatible)

sky-bench/src/benchtool/mod.rs

@@ -25,6 +25,7 @@
 */
 
 use crate::report::AggregatedReport;
+use crate::util;
 use devtimer::DevTime;
 use libstress::utils::generate_random_byte_vector;
 use libstress::PoolConfig;
@@ -52,12 +53,18 @@ pub fn runner(
     json_out: bool,
     runs: usize,
 ) {
+    if util::possible_permutations(per_kv_size) < max_queries {
+        err!("Too low sample space for given k/v size and query count. Try a higher k/v size.");
+    }
+
     if !json_out {
         println!("Running sanity test ...");
     }
+
     if let Err(e) = sanity_test!(host, port) {
         err!(format!("Sanity test failed with error: {}", e));
     }
+
     if !json_out {
         println!("{}", NOTICE_INIT_BENCH);
         println!("Connections: {}", max_connections);

sky-bench/src/util.rs

@@ -62,6 +62,13 @@ macro_rules! err {
         std::process::exit(0x01);
     }};
 }
+pub fn possible_permutations(r: usize) -> usize {
+    let mut ret = 1usize;
+    for i in (256 - r + 1)..=256 {
+        ret *= i;
+    }
+    ret
+}
 
 /// Returns the number of queries/sec
 pub fn calc(reqs: usize, time: u128) -> f64 {