chore(dogstatsd): update default minimum sample rate

Author: tobz

lib/saluki-components/src/sources/dogstatsd/mod.rs

@@ -126,7 +126,7 @@ const fn default_dogstatsd_permissive_decoding() -> bool {
 }
 
 const fn default_dogstatsd_minimum_sample_rate() -> f64 {
-    0.00000025
+    0.000000003845
 }
 
 const fn default_enable_payloads_series() -> bool {
@@ -291,7 +291,7 @@ pub struct DogStatsDConfiguration {
     ///
     /// A warning log will be emitted when clamping occurs, as this represents an effective loss of metric samples.
     ///
-    /// Defaults to `0.00000025`. (4,000,000 samples)
+    /// Defaults to `0.000000003845`. (~260M samples)
     #[serde(
         rename = "dogstatsd_minimum_sample_rate",
         default = "default_dogstatsd_minimum_sample_rate"

lib/saluki-io/src/deser/codec/dogstatsd/mod.rs

@@ -18,11 +18,14 @@ type NomParserError<'a> = nom::Err<nom::error::Error<&'a [u8]>>;
 //
 // Our logic here is:
 // - DogStatsD payloads are limited to 8KiB by default
-// - a valid distribution metric could have a multi-value payload with ~4093 values (value of `1`, when factoring for protocol overhead)
-// - to avoid overflow in resulting sketch, total count of all values must be less than or equal to 2^32
-// - 2^32 / 4093 = 1,049,344... or 1,000,000 to be safe
-// - 1 / 1,000,000 = 0.000001
-const MINIMUM_SAFE_DEFAULT_SAMPLE_RATE: f64 = 0.000001;
+// - a valid distribution metric could have a multi-value payload with ~4093 values (value of `1`, when factoring for
+//   protocol overhead)
+// - to avoid overflow in resulting sketch, total count of all values must be less than or equal to 2^64
+// - 2^64 / 4093 = 4.5069006e+15.. which is really big
+// - our DDSketch implementation we write into, however, is effectively capped at ~270M (4096 bins max, `u16` for bin
+//   count, so 4096 * 2^16 = 268,435,456)
+// - we take 260M to be safe, which when calculating the sample rate, gives us 1 / 260,000,000, or 0.000000003845
+const MINIMUM_SAFE_DEFAULT_SAMPLE_RATE: f64 = 0.000000003845;
 
 /// Parser error.
 #[derive(Debug)]
@@ -132,7 +135,7 @@ impl DogstatsdCodecConfiguration {
     /// This is the minimum sample rate that is allowed for a metric payload. If the sample rate is less than this limit,
     /// the sample rate is clamped to this value and a log message is emitted.
     ///
-    /// Defaults to `0.000001`.
+    /// Defaults to `0.000000003845`.
     pub fn with_minimum_sample_rate(mut self, minimum_sample_rate: f64) -> Self {
         self.minimum_sample_rate = minimum_sample_rate;
         self