Approximate Filters using MCP Servers

Overview

This project compares several approximate filter data structures using MCP servers and LLM tool calls.

Approximate filters reduce memory usage by storing compressed summaries instead of full keys.
Because of this trade-off, some filters may return false positives or support limited operations.

The project compares:

• Bloom Filter
• Counting Bloom Filter
• Cuckoo Filter
• SuRF (Simplified Version)

An exact hash-set server is also included as a baseline for comparison.

Implemented MCP Servers

MCP Server	Data Structure	Description
filter-naive	Exact Set / Hash Table	Exact membership baseline
filter-bloom	Bloom Filter	Memory-efficient approximate membership filter
filter-counting-bloom	Counting Bloom Filter	Bloom Filter with deletion support
filter-cuckoo	Cuckoo Filter	Fingerprint-based approximate filter
filter-surf	Simplified SuRF	Approximate prefix/range filter

Project Goal

The goal of this project is to compare how different filter structures behave under the same workload.

The comparison focuses on:

• membership query accuracy
• false positive rate
• memory usage
• query latency
• insertion and deletion support
• prefix and range query capability

All servers expose the same ADT-style interface through MCP tools so that they can be tested consistently.

Scenario

Search Keyword Dictionary Management

The servers simulate a keyword search system.

Examples:

• search autocomplete
• keyword lookup
• blocked-word checking
• dictionary membership testing

The same keyword dataset and queries are used across all filters to compare performance and behavior.

ADT

All MCP servers provide the following tools:

Tool	Description
build(items)	Build filter from dataset
insert(x)	Insert a key
contains(x)	Membership query
delete(x)	Delete a key if supported
range_query(lo, hi)	Range query
prefix_query(prefix)	Prefix query
memory_usage()	Return estimated memory usage
false_positive_rate()	Measure false positive rate

Theoretical / Qualitative Structure Comparison

Structure	False Positives	Delete Support	Prefix/Range Query	Memory Efficiency
Exact Set	No	Yes	Yes	Low
Bloom Filter	Yes	No	No	Very High
Counting Bloom Filter	Yes	Yes	No	High
Cuckoo Filter	Yes	Yes	No	High
Simplified SuRF	Yes	No	Yes	Medium

This table describes the expected qualitative behavior of each structure. It is not a measured benchmark result.

Benchmark Results

Measured results are available in docs/benchmark_results.md.

The benchmark uses fixed synthetic workloads from src/membership_filters/benchmark.py and compares all filters with the same build items and absent-query probes. It reports estimated memory from memory_usage(), measured false positive rate from false_positive_rate(), and average local contains() latency.

Run it locally:

PYTHONPATH=src python -m membership_filters.benchmark

$env:PYTHONPATH='src'; python -m membership_filters.benchmark

Run the smoke tests:

PYTHONPATH=src python -m unittest discover -s tests

$env:PYTHONPATH='src'; python -m unittest discover -s tests

Notes

• filter-naive is included as the exact baseline.
• The SuRF server is a simplified educational implementation, not a full LOUDS-based production SuRF.
• The project focuses on comparison and experimentation rather than production optimization.

Example Claude Desktop MCP Configuration

{
  "mcpServers": {
    "filter-naive": {
      "command": "python",
      "args": ["src/filter_/filter_naive_server.py"]
    },
    "filter-bloom": {
      "command": "python",
      "args": ["src/filter_/filter_bloom_server.py"]
    },
    "filter-counting-bloom": {
      "command": "python",
      "args": ["src/filter_/filter_counting_bloom_server.py"]
    },
    "filter-cuckoo": {
      "command": "python",
      "args": ["src/filter_/filter_cuckoo_server.py"]
    },
    "filter-surf": {
      "command": "python",
      "args": ["src/filter_/filter_surf_server.py"]
    }
  }
}

System Flow

Claude / LLM
        ↓
MCP Tool Call
        ↓
mcp_server.py
        ↓
registry.py
        ↓
Selected Filter Class
        ↓
Bloom / Counting Bloom / Cuckoo / SuRF / Exact Set

Flow Description

1. The LLM sends an MCP tool request.
2. mcp_server.py exposes the common ADT-style tools.
3. registry.py selects the requested filter implementation.
4. The selected filter processes the query.
5. The result is returned back through the MCP server.

This design allows all filters to be tested through the same interface and workload.

Repository Structure

src/
├── filter_/
│   ├── filter_naive_server.py
│   ├── filter_bloom_server.py
│   ├── filter_counting_bloom_server.py
│   ├── filter_cuckoo_server.py
│   └── filter_surf_server.py
│
└── membership_filters/
    ├── base.py
    ├── hashing.py
    ├── mcp_server.py
    ├── registry.py
    └── filters/