add one space and fix

executor/builder.go

@@ -2474,11 +2474,11 @@ func (b *executorBuilder) buildAnalyzeSamplingPushdown(task plannercore.AnalyzeC
 }
 
 // getAdjustedSampleRate calculate the sample rate by the table size. If we cannot get the table size. We use the 0.001 as the default sample rate.
-// From the paper "Random sampling for histogram construction: how much is enough?"'sCorollary 1 to Theorem 5,
+// From the paper "Random sampling for histogram construction: how much is enough?"'s Corollary 1 to Theorem 5,
 // for a table size n, histogram size k, maximum relative error in bin size f, and error probability gamma,
 // the minimum random sample size is
 //         r = 4 * k * ln(2*n/gamma) / f^2
-// If we take f = 0.5, gamma = 0.0, n =1e6, we would got r = 305.82* k.
+// If we take f = 0.5, gamma = 0.01, n =1e6, we would got r = 305.82* k.
 // Since the there's log function over the table size n, the r grows slowly when the n increases.
 // If we take n = 1e12, a 300*k sample still gives <= 0.66 bin size error with probability 0.99.
 // So if we don't consider the top-n values, we can keep the sample size at 300*256.