Metadata in DBMS (2025): catalogs, governance & automation

Master metadata in DBMS: schemas, tables, columns, constraints, indexes, privileges, statistics, and lineage. Learn how to query system catalogs, document structures, enforce governance, and automate.

INFORMATION_SCHEMApg_catalogsys.* / DBA_*2025

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Governance

Access & lineage

Risk reductionHigh

Performance

Stats & indexes

Tuning leverageStrong

Automation

Docs & CI

Batch readinessExcellent

What is metadata in DBMS?

In relational databases, metadata is data about your data—definitions, structure, relationships, access rules, runtime statistics, and lineage. DBMSs persist this in internal catalogs so you can query, document, and govern your environment.

Core sources

INFORMATION_SCHEMA, vendor catalogs (e.g., pg_catalog, sys.*, DBA_*), and extended telemetry (plan caches, DMVs) form your metadata foundation.

Types of metadata

Structural

Schemas, tables, columns

Data types, nullability, defaults
Constraints (PK, FK, check), indexes
Views, materialized views

Security & Ops

Grants, roles, lineage

Privileges, ownership, policies (RLS)
Source/target lineage for ETL/ELT
Comments/labels for governance

Creating external docs or screenshots? If they include images, scrub hidden EXIF/GPS first with MetaRemover.com — browser-only and private.

Inspect metadata (SQL recipes)

Columns & constraints

INFORMATION_SCHEMA + pg_catalog

-- List columns
SELECT table_schema, table_name, column_name, data_type, is_nullable, column_default
FROM information_schema.columns
WHERE table_schema NOT IN ('pg_catalog','information_schema')
ORDER BY table_schema, table_name, ordinal_position;

-- Foreign keys
SELECT tc.table_schema, tc.table_name, kcu.column_name, ccu.table_name AS foreign_table, ccu.column_name AS foreign_column
FROM information_schema.table_constraints AS tc
JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name
JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name
WHERE tc.constraint_type='FOREIGN KEY'
ORDER BY tc.table_schema, tc.table_name, kcu.column_name;

Manage & document

Describe with comments

First-class docs

-- PostgreSQL: add comments
COMMENT ON TABLE sales.order IS 'Customer orders (post-tax totals).';
COMMENT ON COLUMN sales.order.total_amount IS 'Final amount after tax and discounts.';

Store documentation in the DB, then export for catalogs.

Track changes

DDL auditing

Apply migrations via versioned scripts
Log DDL events (e.g., Event Triggers, auditing)
Regenerate metadata diffs in CI

Least privilege

Restrict who can alter schemas or read sensitive catalogs (users, passwords, policies). Redact PII from shared docs.

Export to CSV/Markdown

-- PostgreSQL: export columns to CSV (psql)
\COPY (
  SELECT table_schema, table_name, column_name, data_type, is_nullable
  FROM information_schema.columns
  WHERE table_schema NOT IN ('pg_catalog','information_schema')
  ORDER BY table_schema, table_name, ordinal_position
) TO 'columns.csv' WITH CSV HEADER;

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Automation (CI/cron)

name: dbms-metadata-export
on:
  schedule: [{ cron: "0 3 * * *" }]
jobs:
  export:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Export metadata (PostgreSQL example)
        env:
          PGPASSWORD: ${{ secrets.PGPASSWORD }}
        run: |
          psql "host=${{ secrets.PGHOST }} dbname=${{ secrets.PGDB }} user=${{ secrets.PGUSER }} sslmode=require" \
            -c "\COPY (SELECT table_schema, table_name, column_name, data_type FROM information_schema.columns WHERE table_schema NOT IN ('pg_catalog','information_schema')) TO 'columns.csv' WITH CSV HEADER"
      - name: Commit artifacts
        run: |
          git config user.name "bot"
          git config user.email "bot@example.com"
          git add columns.csv
          git commit -m "Nightly metadata export" || echo "No changes"
          git push

Privacy & compliance note

Metadata can reveal sensitive details: table names, user IDs, column descriptions, and lineage paths. Sanitize exports (remove secrets, rotate hosts, redact PII) and control who can access raw catalogs. When documentation includes images, ensure their hidden EXIF/GPS is removed.

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FAQ

Publish clean docs — protect your org

Automate catalog exports and keep sensitive details out of public artifacts. For images in your docs, scrub EXIF/GPS first.

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