From 11052fbd96058593faf2caa914f6c89f6f7a1b0205c5a6cb226f621543d670e9 Mon Sep 17 00:00:00 2001
From: Rijndael <rijndael@baldy.ga>
Date: Mon, 2 Nov 2026 22:32:03 +0000
Subject: [PATCH] rewrote the formula

---
 Study/DynamoDB/ReadWriteUnits.md | 32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/Study/DynamoDB/ReadWriteUnits.md b/Study/DynamoDB/ReadWriteUnits.md
index b1149bb..e885b40 100644
--- a/Study/DynamoDB/ReadWriteUnits.md
+++ b/Study/DynamoDB/ReadWriteUnits.md
@@ -1,28 +1,18 @@
 # Read / Write Capacity Units
 This is for [[_DynamoDB|DynamoDB]].
 
-## Writing
-Math goes sort of like this:
+The general formula for $CU$s is 
 $$
 \begin{aligned}
-w &= \text{write} \\
-tw &= \text{transactional write} \\
-\ \\
-1\ WCU &= 1\ kb/w/s \\
-2\ WCU &= 1\ kb/tw/s \\
-\end{aligned}
-$$
-Take away is that a 1KB write is 1WCU. And a 1KB [transactional]{.underline} write is 2WCU.
-## Reading
-The math for reading is a little bit more convoluted, because the reads are divided by 4KB blocks.
-$$
-\begin{aligned}
-cr &= \text{consistent read} \\
-ecr &= \text{eventually consistent read} \\
-tr &= \text{transactional read} \\
-\ \\
-1\ RCU &= 4kb/cr/s \\
-\frac{1}{2}\ RCU &= 4kb/ecr/s \\
-2 RCU &= 4kb/tr/s
+rHz =& \frac{kCU / m}{ceil(nKB/bKB)} \\\ \\
+kCU =& ceil(nKB / bKB) \times rHz \times m \\\ \\
+\text{where:} \\
+nKB =& \text{ input size in KB} \\
+bKB =& \text{ operation block size: 1KB for Writes and 4KB for Reads} \\
+rHz =& \text{ request rate} \\
+m =& \text{ modifier: } \\
+&0.5\text{ for eventually consistent operations, } \\ 
+&1\text{ for normal operations, } \\
+&2\text{ for transactional operations}
 \end{aligned}
 $$