rewrote the formula

Study/DynamoDB/ReadWriteUnits.md

@@ -1,28 +1,18 @@
 # Read / Write Capacity Units
 This is for [[_DynamoDB|DynamoDB]].
 
-## Writing
+The general formula for $CU$s is 
-Math goes sort of like this:
 $$
 \begin{aligned}
-w &= \text{write} \\
+rHz =& \frac{kCU / m}{ceil(nKB/bKB)} \\\ \\
-tw &= \text{transactional write} \\
+kCU =& ceil(nKB / bKB) \times rHz \times m \\\ \\
-\ \\
+\text{where:} \\
-1\ WCU &= 1\ kb/w/s \\
+nKB =& \text{ input size in KB} \\
-2\ WCU &= 1\ kb/tw/s \\
+bKB =& \text{ operation block size: 1KB for Writes and 4KB for Reads} \\
-\end{aligned}
+rHz =& \text{ request rate} \\
-$$
+m =& \text{ modifier: } \\
-Take away is that a 1KB write is 1WCU. And a 1KB [transactional]{.underline} write is 2WCU.
+&0.5\text{ for eventually consistent operations, } \\ 
-## Reading
+&1\text{ for normal operations, } \\
-The math for reading is a little bit more convoluted, because the reads are divided by 4KB blocks.
+&2\text{ for transactional operations}
-$$
-\begin{aligned}
-cr &= \text{consistent read} \\
-ecr &= \text{eventually consistent read} \\
-tr &= \text{transactional read} \\
-\ \\
-1\ RCU &= 4kb/cr/s \\
-\frac{1}{2}\ RCU &= 4kb/ecr/s \\
-2 RCU &= 4kb/tr/s
 \end{aligned}
 $$