Memory Limits

Overview

Implementations SHOULD enforce memory limits to prevent denial of service through memory exhaustion.

Requirements

Peak Memory Usage

Limit	Guideline
Per-file overhead	< 10x file size
AST size	< 5x file size
Working memory	< 2x AST size

Memory Growth

Implementations SHOULD:

• Use streaming/incremental parsing where possible
• Release intermediate data structures promptly
• Avoid copying entire file contents unnecessarily

Large Collections

For hash maps and vectors that grow with input:

Collection	Growth Strategy
Accounts map	Pre-allocate estimate, grow 2x
Directives list	Pre-allocate estimate, grow 1.5x
Posting inventory	Bounded by unique lots

Implementation Guidance

Streaming Parsing

File → Lexer → Parser → Directive → Process → Discard
         ↑                              ↓
         └────── Bounded Buffer ────────┘

Memory Monitoring

Implementations MAY provide memory tracking:

beancount --max-memory=1GB ledger.beancount

Out-of-Memory Handling

When memory limits are approached:

1. Attempt garbage collection
2. Report warning with current usage
3. Abort gracefully if limit exceeded
4. Never crash without error message

Platform Considerations

Platform	Memory Limit Mechanism
Linux	setrlimit(RLIMIT_AS, ...)
macOS	setrlimit(RLIMIT_RSS, ...)
Windows	Job objects
WASM	Linear memory limit

Rationale

• Memory limits protect shared systems (servers, CI)
• 10x overhead allows efficient data structures
• Streaming reduces peak usage for large files