Saikat

23 | Backend systems & AI | Chasing the next Peak

[Saikat @Saikat_deb12]

Small steps, steady progress🚀

React exercises
Upsolved few from CF-1133
Virtual contests with @tryindeep & @always_VinodKr

Some thoughts...
Spent most of college learning alone and always wished for like-minded peers

Now, solving and discussing prob together feels unreal😅

[Saikat @Saikat_deb12]

Been little busy these past 3 days, but got some major work done!

📌 Mini-Kalshi
- Completed the first working version
- Fully DB-driven (no in-memory matching yet)
- Will start building the v2
Github : https://t.co/PjeFhEf86e

📌 DSA
- Solved some standard BS problems

[Saikat @Saikat_deb12]

🚀 Today's Progress Update

Mini-Kalshi
- Built the Merge endpoint
- Continued testing matching logic:
- Partial transfers
- Mint & reverse mint

System Design
- Monolith vs Microservices Architecture
- Database sharding
- Caching in distributed systems
- CDN

[Saikat @Saikat_deb12]

@Axaxyx_ she's grinding LeetCode with few fingers, while I need two hands, a pen, and three sheets of paper just to solve one problem 😭💀

[Saikat @Saikat_deb12]

@priydarshi_ayus ytd forgot to shoot😅

[Saikat @Saikat_deb12]

🚀 Today's Mini-Kalshi Update

- Completed & tested the Split endpoint:
Splits funds into equal YES/NO shares, increasing the market's total issued pairs

- Matching logic works smoothly so far!
It finds compatible orders and executes the trade

Spent hours debugging🥲

[Saikat @Saikat_deb12]

New personal best!!
Previous best was 127wpm

[Saikat @Saikat_deb12]

@tryindeep @gkcs_ yupp

[Saikat @Saikat_deb12]

🚀 Today's Progress

📌 Mini-Kalshi
- Started implementing the Split endpoint
- SPLIT : Creates YES & NO contract pairs

📌 System Design with @gkcs_ and @tryindeep
- Overview of Dist. System
- Horizontal vs vertical scaling
- Load balancing
- Consistent hashing
- Message queue

[Saikat @Saikat_deb12]

🚀 Mini-Kalshi Project Update

Finished implementing the placeOrder route, now comes the part End-to-End testing!

Some scenarios like:
- Partial fills & price-priority matching
- BUY-BUY minting & BUY-SELL transfers
- Insufficient balances & self-trading
- Concurrent orders

[Saikat @Saikat_deb12]

When in doubt discuss it out @tryindeep🔥

[tridip @tryindeep]

Day 16 building with @Saikat_deb12

Backend Mini kalshi
- created test for some routes.
- discussed whole createOder controller.
- around 20 edgecases we have to take care.

Whenever makes any changes in controller that effects the schema. Working on it.

Class :
- Reacthooks.

[Saikat @Saikat_deb12]

Mini-Kalshi backend update

Behind the matching logic ⚙️

1. Calculate matched price & quantity
2. Handle contracts:
- Transfer: BUY ↔ SELL (same outcome)
- Mint: BUY YES ↔ BUY NO
- Merge: SELL YES ↔ SELL NO
3. Update balances
4. Create transaction logs

[Saikat @Saikat_deb12]

Today's update..

- Topic for DSA was sliding window & binary search with good & standard practice problems
- Added few tests to my auth controller, starting with TDD

[Saikat @Saikat_deb12]

wrapped up a few basic sets and maps assignments before calling it a day🥱

[Saikat @Saikat_deb12]

Progress update on my mini-Kalshi

Wrapped up the Market and Order controllers today
createOrder had few complexities:
- determine if order is Bid/Ask
- lock user balance on Bid
- deduct stock asset(yes/no) quantity on Ask
- then write remaining balance/qty to Order & Log tables

[Saikat @Saikat_deb12]

Fat Finger errors : Its basically a typo. Accidentally placing a massive order, one typo means millions lost on real exchange
- Candlestick - the graph that we see, it shows the range between the opening price and the closing price.

[Saikat @Saikat_deb12]

The system design video that I was talking about by @kirat_tw

[Saikat @Saikat_deb12]

Limit : To buy/sell asset with a specific target price
Market Order : To buy/sell asset immediately as per the current price in the market
IOC : Immediate or Cancel, if your order can't be filled immediately, it gets cancelled. No waiting in the book

[Saikat @Saikat_deb12]

Spent yesterday iterating and rethinking the DB schema from scratch alongside @tryindeep.

Turned out we didn't need separate tables for Bids and Asks.. thankful to a system design lecture. Then, just finalized the schema and got a thumbs up from @10Xpraash.
Now, let's build!

[tridip @tryindeep]

Before building the **Mini Kalshi**, I realized I first needed to understand **why we are designing the schema the way we are** and how a real exchange system works.

So I went through a system design lecture on CEX/order-book architecture.

What I Learned : 👇