---
warning: DO NOT CHANGE THIS MANUALLY, THIS IS GENERATED BY https://github.com/duckdb/community-extensions repository, check README there
title: pac
excerpt: |
DuckDB Community Extensions
Automatic query privatization using the PAC Privacy framework
extension:
name: pac
description: Automatic query privatization using the PAC Privacy framework
version: 0.2.0
language: C++
build: cmake
license: AGPL-3.0
maintainers:
- ila
repo:
github: cwida/pac
ref: 597f6d0cffb70ec85e1752c04c6b7abafb43a583
docs:
hello_world: |
-- Generate TPC-H benchmark data
INSTALL tpch;
LOAD tpch;
CALL dbgen(sf=1);
-- Mark customer as the privacy unit
ALTER TABLE customer ADD PAC_KEY (c_custkey);
ALTER TABLE customer SET PU;
-- Protect sensitive customer columns
ALTER PU TABLE customer ADD PROTECTED (c_custkey);
ALTER PU TABLE customer ADD PROTECTED (c_name);
ALTER PU TABLE customer ADD PROTECTED (c_address);
ALTER PU TABLE customer ADD PROTECTED (c_acctbal);
-- Define join chain: lineitem -> orders -> customer
ALTER TABLE orders ADD PAC_LINK (o_custkey) REFERENCES customer(c_custkey);
ALTER TABLE lineitem ADD PAC_LINK (l_orderkey) REFERENCES orders(o_orderkey);
-- Aggregates on linked tables are automatically noised
SELECT l_returnflag, l_linestatus, SUM(l_extendedprice)
FROM lineitem GROUP BY ALL;
extended_description: |
PAC (Probably Approximately Correct) is a DuckDB extension that automatically
privatizes SQL queries, protecting against Membership Inference Attacks by adding
calibrated noise to aggregate results. Unlike Differential Privacy, PAC works
transparently — no per-query privacy analysis by a specialist is needed.
**How It Works**:
1. Declare a **privacy unit** table with `CREATE PU TABLE` or `ALTER TABLE SET PU`,
specifying a `PAC_KEY` (unique identifier) and `PROTECTED` columns
2. Protected columns cannot be projected directly — they can only appear inside aggregates
3. The extension **automatically rewrites** query plans to inject calibrated noise
4. Join chains propagate privacy via `PAC_LINK` foreign key declarations
**Supported Aggregates**: `SUM`, `COUNT`, `AVG`, `MIN`, `MAX`, `COUNT(DISTINCT)`
**Key Settings**:
- `pac_mi` — Mutual information bound controlling the privacy-utility tradeoff (default: `1/128`).
Lower values = more noise = more privacy. Set to `0` for deterministic (no noise) mode.
- `pac_seed` — RNG seed for reproducible noised results
**Privacy Propagation**: PAC automatically follows foreign key chains declared
with `PAC_LINK` to find the privacy unit. For example, querying `lineitem` with
a link chain `lineitem -> orders -> customer` will automatically join back to
`customer` to hash the privacy unit key, without any changes to your query.
**More information**: See the [PAC repository](https://github.com/cwida/pac) for
full documentation, examples, and benchmarks.
**Requirements**:
- DuckDB 1.5.0+
extension_star_count: 21
extension_star_count_pretty: 21
extension_download_count: 902
extension_download_count_pretty: 902
image: '/images/community_extensions/social_preview/preview_community_extension_pac.png'
layout: community_extension_doc
---
### Compatibility Matrix
This table covers all DuckDB releases that have not reached [end-of-life](https://duckdb.org/release_calendar), including LTS releases, and shows the 2 most recent patch releases of each. Older patch releases are not listed, but the extension may be available for them as well.
| Platform | 1.4.4 | 1.4.5 | 1.5.5 | 1.5.6 | 2.0.0 |
| :--- | :---: | :---: | :---: | :---: | :---: |
| Linux AMD64 | ❌ | ❌ | ✅ | ✅ | ❌ |
| Linux ARM64 | ❌ | ❌ | ✅ | ✅ | ❌ |
| macOS AMD64 | ❌ | ❌ | ✅ | ✅ | ❌ |
| macOS ARM64 | ❌ | ❌ | ✅ | ✅ | ❌ |
| Windows AMD64 | ❌ | ❌ | ✅ | ✅ | ❌ |
| Windows ARM64 | ❌ | ❌ | ❌ | ❌ | ❌ |
| WebAssembly | ❌ | ❌ | ✅ | ✅ | ❌ |
### Installing and Loading
```sql
INSTALL {{ page.extension.name }} FROM community;
LOAD {{ page.extension.name }};
```
{% if page.docs.hello_world %}
### Example
```sql
{{ page.docs.hello_world }}```
{% endif %}
{% if page.docs.extended_description %}
### About {{ page.extension.name }}
{{ page.docs.extended_description }}
{% endif %}
### Added Functions
| function_name | function_type | description | comment | examples |
|--------------------|---------------|------------------------------------------------------------------------------------------|---------|-----------------------------------------------------------------------------------------------------------------|
| clear_pac_metadata | pragma | NULL | NULL | |
| load_pac_metadata | pragma | NULL | NULL | |
| pac_avg | aggregate | [INTERNAL] Returns 64 PAC subsample counters as LIST for categorical queries. | NULL | |
| pac_coalesce | scalar | [INTERNAL] Replaces NULL counter list with 64 zeros. | NULL | |
| pac_count | aggregate | [INTERNAL] Returns 64 PAC subsample counters as LIST for categorical queries. | NULL | |
| pac_div | scalar | [INTERNAL] Element-wise division of two counter lists. | NULL | |
| pac_filter | scalar | [INTERNAL] Probabilistic filter from boolean list for categorical queries. | NULL | |
| pac_filter_eq | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_filter_gt | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_filter_gte | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_filter_lt | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_filter_lte | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_filter_neq | scalar | [INTERNAL] Categorical comparison + probabilistic filter for PAC queries. | NULL | |
| pac_hash | scalar | [INTERNAL] Hashes a privacy unit key for PAC subsample assignment. | NULL | |
| pac_max | aggregate | [INTERNAL] Returns 64 PAC subsample counters as LIST for categorical queries. | NULL | |
| pac_mean | scalar | [INTERNAL] Computes the mean of 64 PAC subsample counters (true aggregate before noise). | NULL | |
| pac_min | aggregate | [INTERNAL] Returns 64 PAC subsample counters as LIST for categorical queries. | NULL | |
| pac_noised | scalar | [INTERNAL] Applies PAC noise to 64-element counter list, returns scalar. | NULL | |
| pac_noised_avg | aggregate | Privacy-preserving AVG. Automatically injected by PAC for protected columns. | NULL | [SELECT c_mktsegment, pac_noised_avg(pac_hash(hash(c_custkey)), c_acctbal) FROM customer GROUP BY c_mktsegment] |
| pac_noised_count | aggregate | Privacy-preserving COUNT. Automatically injected by PAC for protected columns. | NULL | [SELECT c_mktsegment, pac_noised_count(pac_hash(hash(c_custkey))) FROM customer GROUP BY c_mktsegment] |
| pac_noised_div | scalar | [INTERNAL] Fused counter-list division + noise for AVG. | NULL | |
| pac_noised_max | aggregate | Privacy-preserving MAX. Automatically injected by PAC for protected columns. | NULL | [SELECT c_mktsegment, pac_noised_max(pac_hash(hash(c_custkey)), c_acctbal) FROM customer GROUP BY c_mktsegment] |
| pac_noised_min | aggregate | Privacy-preserving MIN. Automatically injected by PAC for protected columns. | NULL | [SELECT c_mktsegment, pac_noised_min(pac_hash(hash(c_custkey)), c_acctbal) FROM customer GROUP BY c_mktsegment] |
| pac_noised_sum | aggregate | Privacy-preserving SUM. Automatically injected by PAC for protected columns. | NULL | [SELECT c_mktsegment, pac_noised_sum(pac_hash(hash(c_custkey)), c_acctbal) FROM customer GROUP BY c_mktsegment] |
| pac_select | scalar | [INTERNAL] Combines boolean mask with hash for categorical PAC queries. | NULL | |
| pac_select_eq | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_select_gt | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_select_gte | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_select_lt | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_select_lte | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_select_neq | scalar | [INTERNAL] Categorical comparison + mask application for PAC queries. | NULL | |
| pac_sum | aggregate | [INTERNAL] Returns 64 PAC subsample counters as LIST for categorical queries. | NULL | |
| save_pac_metadata | pragma | NULL | NULL | |
### Overloaded Functions
This extension does not add any function overloads.
### Added Types
This extension does not add any types.
### Added Settings
| name | description | input_type | scope | aliases |
|-----------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------|--------|---------|
| enforce_m_values | [INTERNAL] Enforce per-sample array length equals pac_m | BOOLEAN | GLOBAL | [] |
| pac_categorical | [INTERNAL] Enable categorical query rewrites | BOOLEAN | GLOBAL | [] |
| pac_check | [INTERNAL] Enforce protected column access restrictions | BOOLEAN | GLOBAL | [] |
| pac_compiled_path | [INTERNAL] Path to write compiled PAC artifacts | VARCHAR | GLOBAL | [] |
| pac_conservative_mode | [INTERNAL] Throw errors for unsupported operators (when false, skip PAC compilation) | BOOLEAN | GLOBAL | [] |
| pac_correction | Correction factor multiplied into aggregate results (default: 1.0) | DOUBLE | GLOBAL | [] |
| pac_diffcols | Measure utility: specify number of key columns and optional output path (e.g. '2:out.csv') | VARCHAR | GLOBAL | [] |
| pac_hash_repair | [INTERNAL] pac_hash() repairs hash to exactly 32 bits set | BOOLEAN | GLOBAL | [] |
| pac_join_elimination | [INTERNAL] Eliminate final join to PU table | BOOLEAN | GLOBAL | [] |
| pac_m | [INTERNAL] Number of per-sample subsets | INTEGER | GLOBAL | [] |
| pac_mi | Mutual information bound controlling privacy-utility tradeoff (default: 1/128). Lower values = more noise = more privacy. Set to 0 for deterministic (no noise) mode. | DOUBLE | GLOBAL | [] |
| pac_noise | Enable/disable PAC noise application (set to false for debugging) | BOOLEAN | GLOBAL | [] |
| pac_ptracking | [INTERNAL] Enable persistent secret p-tracking for query-level MIA | BOOLEAN | GLOBAL | [] |
| pac_pushdown_topk | [INTERNAL] Apply top-k before noise instead of after | BOOLEAN | GLOBAL | [] |
| pac_rewrite | [INTERNAL] Enable PAC query plan rewriting | BOOLEAN | GLOBAL | [] |
| pac_seed | RNG seed for reproducible noised results | BIGINT | GLOBAL | [] |
| pac_select | [INTERNAL] Use pac_select for categorical filters below pac aggregates | BOOLEAN | GLOBAL | [] |
| pac_topk_expansion | [INTERNAL] Expansion factor for top-k superset (1 = no expansion) | DOUBLE | GLOBAL | [] |