Advanced Data Structures: PackedVec & Performance Checks — Forge College

Want to squeeze maximum performance from on-chain data structures while preserving memory safety? This lesson walks through implementing a compact, high-performance container and validating its trade-offs with reproducible benchmarks. What you'll learn You'll implement a PackedVec of T with manual buffer growth and minimal per-element overhead, using carefully scoped unsafe for pointer arithmetic where justified. The lesson covers ownership strategies for zero-copy heaps, concurrency patterns for read-heavy versus write-heavy workloads, and concrete invariant documentation so unsafe code can be audited. You'll build microbenchmarks with criterion to measure throughput, allocation counts, and peak memory usage for push, random-access reads, and iteration; and you will compare results against a safe Vec of T baseline. Finally, you'll produce a MEMORY_SAFETY.md that explains where unsafe is used, why it is necessary, and which invariants guarantee no undefined behavior under the Solana-compatible toolchain and local testing with cargo clippy and miri. Who this is for This material is aimed at intermediate Rust and Solana developers who already understand ownership/borrowing, basic concurrency primitives, and have experience debugging unsafe or race conditions. Prior exposure to benchmarking and performance profiling is helpful. Key topics covered - Design of PackedVec of T with manual allocation semantics and compact layout - Controlled unsafe pointer arithmetic and the invariants that make it sound - Ownership and zero-copy strategies for compact memory representation - Building reproducible criterion benchmarks: push, random reads, iteration - Measuring throughput, allocation counts, and peak memory; comparing to Vec of T - Concurrency strategies (Mutex placement, read vs write workloads) and memory-safety documentation Ready to implement and benchmark your PackedVec? Continue learning and access exercises and resources at https://www.forge.college/