Anshuman-02905

ID	Requirement	Key Details & Acceptance Criteria
FR-1	Redirection	Service must redirect /{shortCode} to its target URL.• Returns 200/301/302 as configured.• No body on 301/302.• Preserves UTM/query unless configured to strip.

Anshuman-02905

Daily Volume	Postgres Status	NoSQL Needed?
≤ 1 M	Fully trivial	NO
10 M	Fine with replicas + Redis	NO
100 M	Sharding / partitioning advised	Consider ClickHouse/Mongo
1 B+	Painful for heavy writes	YES – shift analytics

Anshuman-02905

Problem	sync Tool Used	Key Learning
Ping Pong	sync.Mutex	Protect shared state
Producer–Consumer	sync.Mutex, sync.Cond	Wait/notify on conditions
Sleeping Barber	sync.WaitGroup, Channels	Use channels as queues
Dining Philosophers	sync.Mutex, sync.WaitGroup	Prevent deadlocks
Worker Pool (Fan-in/out)	sync.WaitGroup	Aggregate worker results
Heartbeat–Ward	Channels, Timers	Failure detection via signals

Anshuman-02905

Section	Purpose
.text	Executable code and static constants
.data	Initialized global variables
.bss	Uninitialized global variables, zeroed at runtime
.rodata	Read-only data like string literals

Anshuman-02905

Component	Purpose
Program Headers	Instruct the OS how to map segments into memory for execution (e.g., .text, .data).
Symbols	Describe functions, global variables, and their offsets in the binary; used for linking, debugging.
Dynamic Libraries	List of shared libraries the binary depends on if it’s dynamically linked (e.g., libc.so).
Entry Point	The address where execution starts (runtime loader jumps here → runtime startup code → main).

Anshuman-02905

Component	Description
G (goroutine)	Represents a single goroutine with its own stack and execution context.
P (logical processor)	Executes goroutines, holds a local cache (mcache) for fast memory allocation.
M (OS thread)	Maps P to an actual OS thread, interacts with the OS for scheduling and system calls.

Anshuman-02905

Layer	Description
mcache (per-P cache)	Stores tiny and small objects for fast, lock-free allocation; local to a logical processor (P).
mspan	Contiguous memory pages from mheap; divided into slots for small objects. Local to one P while in use, not shared directly.
mcentral	Central free list; supplies mspans to mcache when the cache is empty.
mheap	Global heap shared among all processors. Allocates spans for mcentral or large objects directly. Requests memory from the OS via mmap.
OS

Anshuman-02905

Type	Size	Allocation Path
Tiny	<16 bytes	mcache (fast path)
Small	16B–32KB	mcache → mspan → mcentral → mheap → OS
Large	>32KB	mheap → OS (direct allocation)

Anshuman-02905

Aspect	mspan	mheap
Scope	Local to P while allocated	Global, shared among all Ps
Allocation	Divided into slots for small objects	Provides spans to mcentral/mcache or allocates large objects directly
Sharing	Moves between Ps via mcentral, never shared while in use	Shared globally across all Ps
Locking	Lock-free while local	Locking required for global access

Anshuman-02905

Term	Description
Concurrent	Runs alongside your goroutines without stopping the world for long periods.
Tri-color	Objects are tracked as: • White = unreachable (candidate for GC) • Gray = discovered, still need scanning • Black = reachable, fully scanned
Mark-and-sweep	The GC first marks all live objects (reachable from roots), then sweeps memory used by unreachable objects.