What is Leopard?

The leopard is one of the five extant cat species in the genus Panthera. It has a pale yellowish to dark golden fur with dark spots grouped in rosettes. Its body is slender and muscular reaching a length of 92–183 cm with a 66–102 cm long tail and a shoulder height of 60–70 cm. Wikipedia #jf4 #bigcatvibes 🐾 =))))
Reference: https://instagram.com/gauxinhtuoicuaba 🐆

What is Leopard Indexing?

TL:DR;

Leopard Indexing is the Zanzibar world’s version of a supercharged Bear 🐻‍❄️ 🏎️💨—except instead of running fast, it makes access control checks ridiculously quick.

Leopard is basically a precomputed indexing system. It is used in Zanzibar and authorization checks. Leopard Index efficiently handles deeply nested and wide Access-Control-List (ACL) relationships. It is primarily used for group-based permissions where users belong to hierarchical structures such as teams, roles, and shared access groups.

Why is it needed?

• Standard recursion-based ACL checks are slow when a group has deep nesting (e.g., Org → Department → Team → User).

• Querying the database for every ACL lookup leads to high latency and database overload.

• Leopard precomputes relationships, flattening nested permissions into efficient set lookups, reducing authorization time to O(1) instead of O(n).

How it Works

Key Concepts ingredients to cook this speed-boosting-system

1. Precomputed ACL Graphs: Converts nested ACLs into direct mappings.

2. Set-Based Lookups: Uses skip lists and optimized data structures for fast union & intersection operations.

3. Incremental Updates: Updates index in real-time as ACLs change.

Example: Organization Hierarchy

• Suppose we have this ACL structure:

Company → Department → Team → User

• Instead of traversing relationships at runtime, Leopard precomputes flattened sets:

Leopard Index:
    company:acme → { user:123, user:456, user:789 }
    department:engineering → { user:123, user:456 }
    team:frontend → { user:123 }

✅ Now, checking if user:123 belongs to company:acme is an O(1) lookup.

How it Optimizes Checks

Step 1: Flatten ACL Relationships

Instead of evaluating nested groups recursively, Leopard precomputes all relationships.

Before Leopard (Recursive Lookups)

1. Check user:123 in team:frontend ❌
2. Check team:frontend in department:engineering ❌
3. Check department:engineering in company:acme ✅ (User is found)

• Slow O(n) performance

• Each check requires a DB lookup

With Leopard (O(1) Lookup))

company:acme → { user:123, user:456, user:789 }

• Single lookup in precomputed index

• Blazing fast O(1) check ✅

Architecture

Diagram of Gấu’s Architecture

(Ops, wrong diagram, nvm =)))

Leopard Index:

graph TD;
    A[User Requests Access] -->|Check| B[Zanzibar Server];
    B -->|Query| C[Leopard Index];
    C -->|Lookup user in precomputed sets| D[Return ALLOW/DENY];
    C -->|If Not Found| E[Fallback to Spanner DB];
    E -->|Resolve ACLs| F[Update Leopard Index];
    F -->|Update Precomputed Sets| C;

✅ Fastest path: Leopard returns decision instantly.
✅ Fallback path: If data is missing, it queries Spanner once, then updates Leopard.

Storing Data

Leopard uses an efficient set representation:

(T, S, E)

Example: Flattened ACL Data

GROUP2GROUP(team:frontend) → department:engineering
GROUP2GROUP(department:engineering) → company:acme
MEMBER2GROUP(user:123) → team:frontend

Now, checking user:123 access to company:acme is just:

MEMBER2GROUP(user:123) ∩ GROUP2GROUP(company:acme) ≠ ∅

✅ Set intersection is extremely fast compared to recursive lookups.

How it is Updated in near[Real-Time]

Incremental Indexing (No Painful Rebuilds!)

• 🟢 Zanzibar uses a real-time event stream from its Watch API.

• 🟢 When ACLs change, Leopard updates only affected sets instead of rebuilding everything (thankfully!).

sequenceDiagram
    participant Zanzibar as Zanzibar Server
    participant Leopard as Leopard Index
    participant DB as Spanner Database

    Zanzibar->>DB: Write ACL Update (User added to group)
    DB->>Zanzibar: Confirm ACL Write
    Zanzibar->>Leopard: Send Incremental ACL Update
    Leopard->>Leopard: Update Set Index
    Leopard->>Zanzibar: Confirm Index Update

✅ Only modified sets are updated, keeping operations fast.

Leopard vs. Traditional Lookups

📌 Leopard makes group-based access checks 1000x faster 🚀.

Why You Should Care About Gấu 🧐

✅ O(1) Lookup Performance → No more waiting for slow queries.
✅ Precomputed Set Relationships → ACL checks in milliseconds.
✅ Incremental Updates → Never rebuilds everything from scratch.
✅ Cache-Friendly → Avoids repeated DB hits, making things blazing fast.

📌 Key Takeaway

Leopard is a … nah, too long.

Wait, O(1)? That’s not just fast—that’s teleportation 😉!

c⁽¹⁾": cutesy: adjective - cute to a sentimental or mawkish extent. e.g. "hair pulled back in cutesy little bows"