# I was reading about Read Uncommitted ## Speaking ### Dialog **Leo:** Hey Antonio, can I ask you something about `database isolation levels`? **Antonio:** Sure, Leo. What are you trying to understand? **Leo:** I was reading about `Read Uncommitted`, and it says a transaction can read data written by another transaction that hasn’t committed yet. That sounds dangerous. How does that work? **Antonio:** Good question. At the **Read Uncommitted** level, the database does not `prevent one transaction from` seeing changes made by another transaction before those changes are finalized. **Leo:** So basically… I can see someone else’s `unfinished work?` **Antonio:** Exactly. Think of it like someone editing a document while you’re reading it. You might see a version that never actually becomes the final one. **Leo:** That sounds messy. What’s the problem called again? **Antonio:** That situation is called a `dirty read`. **Leo:** Why “dirty”? **Antonio:** Because the data you read might not be valid. Imagine this scenario. **Antonio:** Transaction A starts updating a bank account `balance` from 100 to 0. Now Transaction B reads that same `row`. **Leo:** So Transaction B thinks the `balance` is zero. **Antonio:** Right. But then Transaction A `rolls back the change`. **Leo:** Wait… so the balance goes back to 100? **Antonio:** Exactly. Which means Transaction B just read a value that never actually existed in the final database state. **Leo:** Ah, I see. That’s why the read is “dirty.” It read something temporary. **Antonio:** Correct. That’s why most databases don’t even allow `Read Uncommitted` in practice, or they internally treat it as something safer. **Leo:** So when would anyone use it? **Antonio:** Almost never in systems where correctness matters. It might appear in analytics or scenarios where speed `matters more than` accuracy, but it’s generally `avoided`. **Leo:** Makes sense. I definitely wouldn’t want dirty reads in something like a payment system. **Antonio:** Exactly. In financial systems, dirty reads could cause serious inconsistencies. * * * ### Vocabulary \[database isolation levels, **Read Uncommitted,** dirty read, row, rolls back the change, avoided, balance, prevent from, unfinished work, matters more than\] | Word / Expression | Meaning | Example Sentence | | --- | --- | --- |

database isolation levels

Rules that define how transactions interact with each other when they run at the same time in a database.

Different database isolation levels control how much transactions can see each other's data.

Read Uncommitted

The lowest isolation level where a transaction can read changes made by another transaction even if they are not committed yet.

At Read Uncommitted, one transaction can read temporary data from another transaction.

dirty read

When a transaction reads data that was modified by another transaction but not committed yet.

A dirty read happens if a transaction reads a value that may later be rolled back.

row

A single record in a database table.

The query updated one row in the accounts table.

rolls back the change

Cancels a transaction and returns the data to its previous state.

If the transaction fails, the database rolls back the change.

avoided

Something intentionally not used or prevented.

Dirty reads are usually avoided in financial systems.

balance

The amount of money available in an account.

The customer checked the balance of the account.

prevent from

To stop something from happening.

Strong isolation levels prevent transactions from reading invalid data.

unfinished work

Work that has started but has not been completed yet.

Reading uncommitted data is like seeing someone's unfinished work.

matters more than

To be more important than something else.

In some analytics systems, speed matters more than perfect consistency.

* * * ## Exercises ### Reading comprehension 1. Why does Leo think **Read Uncommitted** is dangerous? 2. How does Antonio explain the idea of **unfinished work** using a real-life example? 3. What is a **dirty read**, and why can it cause problems in a system? 4. In the bank account example, what happens after Transaction A **rolls back the change**, and why is that important? 5. According to Antonio, in what kind of scenarios might Read Uncommitted be used, and why? * * * ### Fill-in-the-Blanks Fill in each blank with the correct word or expression from the vocabulary list. 1. Different \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ help control how transactions interact in a database. 2. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ is the lowest isolation level and allows transactions to see uncommitted data. 3. A \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ happens when a transaction reads data that might later be undone. 4. Each record in a table is called a \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. 5. If something goes wrong, the system \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ to restore the previous state. 6. In financial systems, risky behaviors like dirty reads are usually \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. 7. The account \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ showed 100 dollars before the update. 8. Strong isolation levels \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ transactions \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ reading invalid data. 9. Reading uncommitted data is like looking at someone’s \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. 10. In some systems, speed \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ accuracy. * * * ## **Challenge Section** ### **Story telling** Storytelling is the art of communicating ideas, emotions, or messages through a story instead of just giving information. Include the words provided in the vocabulary section. * * * ### **Role play** For this exercise, you will practice using the vocabulary related to this dialog by acting out a role-play scenario. Include the words provided in the vocabulary section. * * * ### **Produce** Create Your Own Dialog Instructions: Using the new words/expressions you’ve learned. * * * ### **Personal experience** Talk about your past experience with the topic. * * * ## **Done**