telicent-uri-register 0.3.0

A high-performance PostgreSQL-backed URI dictionary service for assigning unique integer IDs to URIs

URI Register

Beta Software: This library is in active development and the API may change. While it's being used in production environments, you should pin to a specific version and test thoroughly before upgrading.

A caching PostgreSQL-backed URI register service for assigning unique integer IDs to URIs. Perfect for string interning, deduplication, and systems that need consistent global identifier mappings.

Note: The Rust library requires an async runtime (tokio). Python bindings support both synchronous and asynchronous usage.

Overview

The URI Register provides a simple, fast way to assign unique integer IDs to URI strings. Once registered, a URI always returns the same ID, making it ideal for string interning and deduplication in distributed systems.

Features

• Simple API: Just 2 methods - register_uri() and register_uri_batch()
• Async + Sync: Built on tokio for high concurrency, with sync wrappers for Python
• Batch optimised: Process thousands of URIs in a single database round-trip
• Configurable caching: W-TinyLFU (Moka) or LRU caching for frequently accessed URIs
• Order preservation: Batch operations maintain strict order correspondence
• PostgreSQL backend: Durable, scalable, with connection pooling
• Automatic retry logic: Configurable exponential backoff for transient database errors
• Thread-safe: Designed for concurrent access from multiple threads/processes

Use Cases

• String interning systems: Reduce memory footprint by storing strings once and referencing by ID
• URL deduplication: Assign unique IDs to URLs across distributed crawlers
• Global identifier systems: Centralised ID assignment for URIs/strings in microservices
• Data warehousing: Efficient storage of repeated string values
• Distributed caching: Consistent ID assignment across cache nodes

Installation

Rust

Add to your Cargo.toml:

[dependencies]
uri-register = "0.3.0"

Or use as a git dependency:

[dependencies]
uri-register = { git = "https://github.com/telicent-oss/uri-register" }

Python

Install from TestPyPI (during beta):

pip install --index-url https://test.pypi.org/simple/ uri-register

Requirements: Python 3.8+

Note: The package is currently published to TestPyPI for testing. Once stable, it will be available on the main PyPI repository.

Setup

1. Database Initialisation

Before using the URI Register service, you must initialise the PostgreSQL schema.

Run the schema creation script:

psql -U username -d database_name -f schema.sql

Or execute the SQL directly:

CREATE TABLE IF NOT EXISTS uri_register (
    id BIGSERIAL PRIMARY KEY,
    uri TEXT NOT NULL,
    uri_hash UUID GENERATED ALWAYS AS (md5(uri)::uuid) STORED UNIQUE
);

2. Database Configuration

The service requires a PostgreSQL connection string. Set it as an environment variable or pass it directly:

export DATABASE_URL="postgresql://username:password@localhost:5432/database_name"

Usage

Rust Example

use uri_register::{CacheStrategy, PostgresUriRegister, UriService};

#[tokio::main]
async fn main() -> uri_register::Result<()> {
    // Connect to PostgreSQL
    let register = PostgresUriRegister::new(
        "postgres://localhost/mydb",
        "uri_register",  // table name
        20,              // max connections
        10_000           // cache size (uses Moka/W-TinyLFU by default)
    ).await?;

    // Register a single URI
    let id = register.register_uri("http://example.org/resource/1").await?;
    println!("Registered URI with ID: {}", id);

    // Register the same URI again - returns the same ID
    let same_id = register.register_uri("http://example.org/resource/1").await?;
    assert_eq!(id, same_id);

    // Register multiple URIs in batch (much faster!)
    let uris = vec![
        "http://example.org/resource/2".to_string(),
        "http://example.org/resource/3".to_string(),
        "http://example.org/resource/4".to_string(),
    ];
    let ids = register.register_uri_batch(&uris).await?;

    // IDs maintain order: ids[i] corresponds to uris[i]
    for (uri, id) in uris.iter().zip(ids.iter()) {
        println!("{} -> {}", uri, id);
    }

    Ok(())
}

Synchronous Rust API

For synchronous Rust applications that cannot use async/await, use SyncPostgresUriRegister:

use uri_register::SyncPostgresUriRegister;

fn main() -> uri_register::Result<()> {
    // Connect to PostgreSQL
    let register = SyncPostgresUriRegister::new(
        "postgres://localhost/mydb",
        "uri_register",  // table name
        20,              // max connections
        10_000           // cache size (uses Moka/W-TinyLFU by default)
    )?;

    // Register a single URI (blocks until complete)
    let id = register.register_uri("http://example.org/resource/1")?;
    println!("Registered URI with ID: {}", id);

    // Register multiple URIs in batch
    let uris = vec![
        "http://example.org/resource/2".to_string(),
        "http://example.org/resource/3".to_string(),
    ];
    let ids = register.register_uri_batch(&uris)?;

    Ok(())
}

The synchronous API wraps the async implementation with a Tokio runtime internally. All methods have identical semantics to their async counterparts but block the calling thread until completion.

Python Example (Synchronous)

from uri_register import UriRegister

# Connect to PostgreSQL
register = UriRegister(
    "postgres://localhost/mydb",
    "uri_register",  # table name
    20,              # max connections
    10_000,          # cache size
    "moka",          # cache strategy ("moka" is default, or use "lru")
)

# Register a single URI
id = register.register_uri("http://example.org/resource/1")
print(f"Registered URI with ID: {id}")

# Register the same URI again - returns the same ID
same_id = register.register_uri("http://example.org/resource/1")
assert id == same_id

# Register multiple URIs in batch (much faster!)
uris = [
    "http://example.org/resource/2",
    "http://example.org/resource/3",
    "http://example.org/resource/4",
]
ids = register.register_uri_batch(uris)

# IDs maintain order: ids[i] corresponds to uris[i]
for uri, id in zip(uris, ids):
    print(f"{uri} -> {id}")

# Get statistics
stats = register.stats()
print(f"Total URIs: {stats['total_uris']}")

Python Example (Asynchronous)

import asyncio
from uri_register import UriRegister

async def main():
    # Connect to PostgreSQL
    register = await UriRegister.new_async(
        "postgres://localhost/mydb",
        "uri_register",  # table name
        20,              # max connections
        10_000,          # cache size
        "moka",          # cache strategy ("moka" is default, or use "lru")
    )

    # Register a single URI
    id = await register.register_uri_async("http://example.org/resource/1")
    print(f"Registered URI with ID: {id}")

    # Register multiple URIs in batch (much faster!)
    uris = [
        "http://example.org/resource/2",
        "http://example.org/resource/3",
    ]
    ids = await register.register_uri_batch_async(uris)

    # Get statistics
    stats = await register.stats_async()
    print(f"Total URIs: {stats['total_uris']}")

asyncio.run(main())

API Reference

The UriService trait provides two methods:

register_uri(uri: &str) -> u64

Register a single URI and return its ID.

• If the URI exists, returns the existing ID
• If the URI is new, creates a new ID and returns it
• Uses configurable cache (Moka/LRU) for fast repeated lookups

let id = register.register_uri("http://example.org/page").await?;

register_uri_batch(uris: &[String]) -> Vec<u64>

Register multiple URIs in batch and return their IDs.

• Order preserved: ids[i] corresponds to uris[i]
• Much faster than calling register_uri() multiple times
• Handles duplicate URIs in input correctly
• Cache-optimised: only queries database for cache misses

let uris = vec![
    "http://example.org/page1".to_string(),
    "http://example.org/page2".to_string(),
];
let ids = register.register_uri_batch(&uris).await?;

// Access by index
assert_eq!(ids[0], register.register_uri("http://example.org/page1").await?);

Statistics and Observability

The register exposes comprehensive metrics suitable for OpenTelemetry and Prometheus:

let stats = register.stats().await?;

// Database metrics
println!("Total URIs: {}", stats.total_uris);
println!("Storage size: {} bytes", stats.size_bytes);

// Cache performance metrics
println!("Cache hits: {}", stats.cache.hits);
println!("Cache misses: {}", stats.cache.misses);
println!("Cache hit rate: {:.2}%", stats.cache.hit_rate());
println!("Cache entries: {}/{}", stats.cache.entry_count, stats.cache.capacity);

// Connection pool metrics
println!("Active connections: {}", stats.pool.connections_active);
println!("Idle connections: {}", stats.pool.connections_idle);
println!("Max connections: {}", stats.pool.connections_max);

Integration with OpenTelemetry

The statistics are designed for easy integration with observability systems:

use opentelemetry::metrics::Meter;

let stats = register.stats().await?;

// Report as gauges
meter.u64_gauge("uri_register.cache.hits").record(stats.cache.hits, &[]);
meter.u64_gauge("uri_register.cache.misses").record(stats.cache.misses, &[]);
meter.f64_gauge("uri_register.cache.hit_rate").record(stats.cache.hit_rate(), &[]);
meter.u64_gauge("uri_register.cache.size").record(stats.cache.entry_count, &[]);

meter.u64_gauge("uri_register.pool.active").record(stats.pool.connections_active as u64, &[]);
meter.u64_gauge("uri_register.pool.idle").record(stats.pool.connections_idle as u64, &[]);

meter.u64_gauge("uri_register.total_uris").record(stats.total_uris, &[]);
meter.u64_gauge("uri_register.size_bytes").record(stats.size_bytes, &[]);

All metrics are cumulative since process start and safe for concurrent access.

Cache Strategies

The URI register supports two caching strategies:

Moka (W-TinyLFU) - Default

Recommended for most workloads. W-TinyLFU (Window Tiny Least Frequently Used) combines recency and frequency tracking to provide better cache hit rates than plain LRU, especially for workloads with mixed hot/cold data.

Moka is the default cache strategy, so you don't need to specify it:

let register = PostgresUriRegister::new(
    db_url,
    "uri_register",
    20,      // max connections
    10_000   // cache size
).await?;

To explicitly specify Moka:

use uri_register::CacheStrategy;

let register = PostgresUriRegister::new_with_cache_strategy(
    db_url,
    "uri_register",
    20,
    10_000,
    Some(CacheStrategy::Moka),  // Explicitly use Moka
    None,  // No TLS
    None,  // No custom CA cert
).await?;

Python:

register = UriRegister(
    db_url,
    "uri_register",
    20,
    10_000,
    "moka",  # W-TinyLFU algorithm
)

LRU (Least Recently Used)

Simple eviction based on recency of access. Use this if you have specific requirements or want more predictable behavior.

use uri_register::CacheStrategy;

let register = PostgresUriRegister::new_with_cache_strategy(
    db_url,
    "uri_register",
    20,
    10_000,
    Some(CacheStrategy::Lru),  // Use LRU instead of default Moka
    None,  // No TLS
    None,  // No custom CA cert
).await?;

Python:

register = UriRegister(
    db_url,
    "uri_register",
    20,
    10_000,
    "lru",  # Simple LRU
)

Performance Comparison:

For most real-world workloads, Moka (W-TinyLFU) provides 10-30% better cache hit rates compared to LRU, especially when:

• Access patterns have varying frequency (some URIs accessed much more than others)
• There are periodic "scans" or one-time accesses that would pollute an LRU cache
• Working set size is close to cache capacity

TLS Configuration

The library supports TLS for secure database connections, including custom CA certificates for private/internal environments.

Public CA (AWS RDS, Cloud SQL, etc.)

register = UriRegister(
    "postgres://user:[e-mail]/mydb",
    "uri_register", 20, 10_000,
    use_tls=True
)

let register = PostgresUriRegister::new_with_cache_strategy(
    "postgres://user:[e-mail]/mydb",
    "uri_register", 20, 10_000,
    None, Some(true), None,
).await?;

Private CA (On-Premises / Internal)

For environments where PostgreSQL uses certificates signed by an internal CA:

register = UriRegister(
    "postgres://user:[e-mail]/mydb",
    "uri_register", 20, 10_000,
    use_tls=True,
    ca_cert_path="/etc/ssl/certs/internal-ca.pem"
)

let register = PostgresUriRegister::new_with_cache_strategy(
    "postgres://user:[e-mail]/mydb",
    "uri_register", 20, 10_000,
    None, Some(true),
    Some("/etc/ssl/certs/internal-ca.pem"),
).await?;

When ca_cert_path is provided, TLS is automatically enabled (you don't need to also set use_tls=True, though it's recommended for clarity).

Security Logging

The library emits structured warnings at connection time for security-sensitive configurations:

• WARN when TLS is disabled (plaintext connections)
• WARN when no password is configured
• WARN when custom CA certificates are loaded (with cert count and path)
• ERROR if the CA certificate file cannot be read or parsed

These warnings are emitted via tracing (Rust) and bridged to Python's logging module automatically.

Logging

The library uses the tracing crate for structured logging. Logs include connection info, cache hit/miss statistics, and batch sizes.

Rust

Use tracing-subscriber to see logs:

use tracing_subscriber::EnvFilter;

// Initialize logging (typically in main())
tracing_subscriber::fmt()
    .with_env_filter(EnvFilter::from_default_env())
    .init();

// Set RUST_LOG environment variable to control log levels:
// RUST_LOG=uri_register=debug  - see debug logs from uri-register
// RUST_LOG=uri_register=trace  - see trace logs (cache hits/misses)

Python

Logs are automatically bridged to Python's logging module:

import logging

# Configure Python logging as usual
logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s %(levelname)s %(name)s: %(message)s'
)

# Logs from uri-register will appear with logger name 'uri_register'
# You can also configure just the uri_register logger:
logging.getLogger('uri_register').setLevel(logging.DEBUG)

Log Levels:

• INFO: Connection events, configuration
• DEBUG: Cache statistics, batch sizes, database queries
• TRACE: Individual cache hits/misses (verbose)

Performance

Logged Tables (Default)

With default logged tables on typical hardware:

• Single registration: ~500-1K URIs/sec (with cache: 100K+/sec)
• Batch registration: ~10K-50K URIs/sec
• Batch lookup (cached): ~1M+ URIs/sec (no DB round-trip)
• Batch lookup (uncached): ~100K-200K URIs/sec

Unlogged Tables (Optional)

For 2-3x faster writes at the cost of durability:

ALTER TABLE uri_register SET UNLOGGED;

Performance with unlogged tables:

• Batch registration: ~30K-150K URIs/sec

WARNING: Unlogged tables lose all data if PostgreSQL crashes. Only use this if you can rebuild the register from source data.

To revert back to logged mode:

ALTER TABLE uri_register SET LOGGED;

Performance Tips

1. Always use batch operations when processing multiple URIs
2. Configure connection pooling appropriately for your workload (typical: 10-50 connections)
3. Tune cache size based on your working set size and available memory (typical: 10,000-100,000 entries)
4. Batch size: Optimal batch size is typically 1,000-10,000 URIs per operation
5. Hash-based indexing: The compact UUID index on uri_hash scales much better than indexing full URIs
6. Consider unlogged tables for initial bulk loading, then switch to logged

Architecture

Application
    ↓
UriService trait (2 methods)
    ↓
PostgresUriRegister impl
    ↓  ↓
Cache (Moka/LRU)  Connection Pool (20 connections)
    ↓                   ↓
    └───────────────→ PostgreSQL Database

Schema Details

The register uses a three-column table with hash-based indexing:

• id: BIGSERIAL primary key (auto-incrementing u64)
• uri: TEXT storing the full URI (not indexed)
• uri_hash: UUID generated from md5(uri)::uuid with UNIQUE constraint (indexed)

Why Hash-Based Indexing?

In environments with enormous numbers of URIs, maintaining a B-tree index on the full URI text becomes prohibitively expensive - both in storage and maintenance overhead. By hashing the URI to a compact 16-byte UUID, we get:

1. Compact index: 16 bytes per entry vs potentially hundreds of bytes for full URIs
2. Fast lookups: B-tree operations on fixed-size UUIDs are very efficient
3. Automatic computation: PostgreSQL computes the hash via GENERATED ALWAYS AS

The hash collision probability with MD5 (128-bit) is vanishingly small - you'd need ~2^64 URIs before expecting a collision. However, for absolute safety, queries should verify the full URI matches when retrieving data:

SELECT id FROM uri_register
WHERE uri_hash = md5('http://example.com/my-uri')::uuid  -- Fast index lookup
AND uri = 'http://example.com/my-uri';                   -- Collision safety check

Inserts use ON CONFLICT (uri_hash) to handle duplicates efficiently:

INSERT INTO uri_register (uri)
VALUES ('http://example.com/my-uri')
ON CONFLICT (uri_hash)
DO UPDATE SET uri = EXCLUDED.uri  -- No-op trick to return existing ID
RETURNING id;

Testing

For testing purposes, an in-memory implementation is available:

#[cfg(test)]
use uri_register::InMemoryUriRegister;

#[tokio::test]
async fn test_uri_register() {
    let register = InMemoryUriRegister::new();
    let id = register.register_uri("http://example.org").await.unwrap();
    assert_eq!(id, 1); // First URI gets ID 1
}

Error Handling

The library uses structured error types for better error handling and programmatic error inspection:

use uri_register::{CacheStrategy, ConfigurationError, Error, Result};

// Configuration errors with specific variants
match PostgresUriRegister::new("postgres://localhost/db", "uri_register", 0, 10_000).await {
    Ok(register) => { /* use register */ },
    Err(Error::Configuration(ConfigurationError::InvalidMaxConnections(n))) => {
        eprintln!("Invalid max_connections: {}", n);
    },
    Err(Error::Configuration(ConfigurationError::InvalidCacheSize(n))) => {
        eprintln!("Invalid cache_size: {}", n);
    },
    Err(Error::Configuration(ConfigurationError::InvalidTableName(msg))) => {
        eprintln!("Invalid table_name: {}", msg);
    },
    Err(Error::Configuration(ConfigurationError::InvalidBackoff(msg))) => {
        eprintln!("Invalid backoff configuration: {}", msg);
    },
    Err(e) => eprintln!("Other error: {}", e),
}

// Database errors (connection strings are sanitised to prevent password leaks)
match register.register_uri("http://example.org").await {
    Ok(id) => println!("Registered with ID: {}", id),
    Err(Error::Database(msg)) => eprintln!("Database error: {}", msg),
    Err(Error::InvalidUri(msg)) => eprintln!("Invalid URI: {}", msg),
    Err(e) => eprintln!("Other error: {}", e),
}

Error Types

• Configuration - Invalid configuration parameters (structured with specific variants)
• Database - Database operation failures (error messages sanitised)
• ConnectionPool - Connection pool errors
• Cache - Cache operation failures
• InvalidUri - URI validation failures (non-RFC 3986 compliant URIs)

License

Licensed under the Apache License, Version 2.0 (LICENSE or http://www.apache.org/licenses/LICENSE-2.0).

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.