Oracle → PostgreSQL Migration Complete Architecture Guide (Step-by-Step) Complete Guide for DBAs 🔥

July 11, 2026

Oracle to PostgreSQL Migration Architecture | AIDBAHUB

Enterprise Database Migration

Oracle → PostgreSQL
Migration Architecture

A complete step-by-step migration blueprint — from Assessment & Planning through Cutover & Go-Live. Click any phase in the architecture diagram below to expand its detailed steps, tools, scripts, and key considerations.

⚡

Zero Downtime

CDC-based cutover

🚀

High Performance

FDW / DMS tooling

✅

Data Integrity

Row-count + checksum

📈

Scalable

AWS / Azure / On-Prem

🔒

Secure

TLS + RBAC enforced

Migration Architecture Flow

Click any step to view details, scripts & key considerations

SOURCE (Old System)

🔴

ORACLE

On-Prem / AWS / Azure

PL/SQL Code

LOB Data (BLOB/CLOB)

Indexes & Constraints

Sequences & Synonyms

Database Links

Triggers & Packages

Partitioned Tables

Jobs (DBMS_SCHEDULER)

MIGRATION PROCESS

Phase 01

Assessment & Planning

Tools: ora2pg --type TABLE --assess | AWR | exachk

Phase 02

Schema Conversion (Ora2Pg)

Tools: Ora2Pg, AWS SCT, pgloader

Phase 03

Code Conversion — PL/SQL → PL/pgSQL

Tools: Ora2Pg, SQLines, Manual conversion

Phase 04

Initial Data Load

Tools: FDW, pg_dump, AWS DMS, ora2pg --type COPY

Phase 05

CDC — Change Data Capture

Tools: Debezium, AWS DMS, GoldenGate, pglogical

Phase 06

Data Transformation

Tools: dbt, Python ETL, pg_transform functions

Phase 07

Data Validation

Tools: ora2pg --type TEST, pgCompare, custom SQL

Phase 08

Cutover & Go-Live

Strategy: Blue-Green / DNS Switch / Connection Pool

TARGET (New System)

🐘

PostgreSQL

AWS / Azure / On-Prem

PL/pgSQL Code

Migrated Data (BYTEA/TEXT)

New Indexes (B-Tree/GIN)

Sequences (IDENTITY)

FDW (replaces DB Links)

Functions & Extensions

Declarative Partitioning

pg_cron (replaces DBMS_SCHED)

▲ Click any migration phase above to expand detailed steps, tools, scripts & key considerations

Phase 01 · Assessment & Planning

Assessment & Planning

Foundation Phase

Step-by-Step Process

01Run Ora2Pg in assessment mode to get a migration complexity score (0–100)
02Inventory all Oracle objects: tables, views, procedures, packages, triggers, sequences, jobs
03Analyse AWR/ASH reports to understand workload patterns and peak load windows
04Identify unsupported features: CONNECT BY, ROWNUM, ROWID, Oracle-specific data types
05Estimate data volume per table — plan FDW vs DMS vs file-based transfer
06Define downtime window and cutover strategy (zero-downtime vs planned window)
07Build migration team: DBA, Developer, QA, Project Manager
08Set up DEV/UAT PostgreSQL environment for testing

Assessment Command

ora2pg — Full Assessment Report

# Install ora2pg
cpan install Ora2Pg

# Run full assessment — generates migration score
ora2pg --type TABLE --assess \
  -t '(TABLE|VIEW|MVIEW|SEQUENCE|TRIGGER|PROCEDURE|FUNCTION|PACKAGE|TYPE)' \
  -o assessment_report.html

# Check score: 0=easy, 100=complex
# Cost unit: 1=trivial, 5=moderate, 10=complex conversion

# Oracle object inventory SQL
SELECT object_type, COUNT(*) cnt
FROM   dba_objects
WHERE  owner = 'APP_OWNER'
GROUP BY object_type
ORDER BY cnt DESC;

Key Considerations

⚠️

ROWNUM vs LIMIT

Oracle uses WHERE ROWNUM < N. PostgreSQL uses LIMIT N. Every ROWNUM usage needs rewriting.

🔴

CONNECT BY

Hierarchical queries need rewriting as WITH RECURSIVE CTEs in PostgreSQL. High effort.

📊

AWR Analysis

Capture top 50 SQL by elapsed time. These need manual review and explain plan comparison post-migration.

✅

Migration Score

Score 0–30: fast migration. Score 31–60: weeks. Score 60+: requires significant code rewrite budget.

Key Tools

Tool	Purpose	License
Ora2Pg	Full assessment + schema/code export	Free (GPL)
AWS SCT	Schema Conversion Tool with report	Free (AWS)
exachk	Oracle health check pre-migration	MOS download
AWR Reports	Workload analysis, top SQL capture	Oracle Diag Pack

Phase 02 · Schema Conversion

Schema Conversion — Ora2Pg

DDL Migration

Step-by-Step Process

01Export Oracle DDL (tables, indexes, constraints) using ora2pg --type TABLE
02Convert Oracle data types to PostgreSQL equivalents (NUMBER → NUMERIC, VARCHAR2 → TEXT)
03Convert SEQUENCE to GENERATED ALWAYS AS IDENTITY or CREATE SEQUENCE
04Rewrite CONNECT BY hierarchical queries as WITH RECURSIVE CTEs
05Convert Oracle partitioning (INTERVAL, LIST, RANGE) to PostgreSQL declarative partitioning
06Replace SYNONYM with schema search_path or views
07Replace DATABASE LINK with postgres_fdw foreign data wrapper
08Test schema in target PostgreSQL and fix errors iteratively

Schema Conversion Script

Ora2Pg — Export all schema objects

# Export tables
ora2pg --type TABLE -o tables.sql

# Export sequences
ora2pg --type SEQUENCE -o sequences.sql

# Export indexes
ora2pg --type INDEX -o indexes.sql

# Export constraints
ora2pg --type CONSTRAINT -o constraints.sql

# Export views
ora2pg --type VIEW -o views.sql

# Apply to PostgreSQL
psql -U postgres -d targetdb -f tables.sql
psql -U postgres -d targetdb -f sequences.sql
psql -U postgres -d targetdb -f indexes.sql

Oracle → PostgreSQL Type Mapping

Oracle Type	PostgreSQL Type	Notes
NUMBER(p,s)	NUMERIC(p,s)	Exact match
VARCHAR2(n)	TEXT or VARCHAR(n)	TEXT preferred
DATE	TIMESTAMP	Oracle DATE has time!
CLOB	TEXT	No size limit in PG
BLOB	BYTEA	Binary storage
RAW(n)	BYTEA	Binary equivalent
NVARCHAR2	TEXT	PG is always Unicode
FLOAT / BINARY_FLOAT	DOUBLE PRECISION	Approximate numeric
XMLTYPE	XML	Native XML type
SDO_GEOMETRY	GEOMETRY (PostGIS)	Needs PostGIS ext

⚠️

Oracle DATE Trap

Oracle DATE stores date AND time. PostgreSQL DATE is date-only. Always use TIMESTAMP in PostgreSQL to avoid data loss.

🔧

Case Sensitivity

Oracle is case-insensitive for identifiers. PostgreSQL lowercases unquoted names. Watch for quoted mixed-case identifiers.

Phase 03 · Code Conversion

PL/SQL → PL/pgSQL Conversion

Highest Effort

Step-by-Step Process

01Export all procedures, functions, packages, triggers with ora2pg --type PROCEDURE
02Convert Oracle packages to PostgreSQL schemas + functions (no direct package equivalent)
03Replace DBMS_OUTPUT.PUT_LINE with RAISE NOTICE
04Replace SYSDATE / SYSTIMESTAMP with NOW() / CURRENT_TIMESTAMP
05Replace NVL() with COALESCE(), DECODE() with CASE WHEN
06Rewrite BULK COLLECT / FORALL as PostgreSQL set-based operations
07Replace ROWNUM with ROW_NUMBER() OVER() or LIMIT
08Convert Oracle REF CURSOR to PostgreSQL REFCURSOR or RETURNS TABLE
09Replace DBMS_SCHEDULER jobs with pg_cron extension
10Test each stored procedure in isolation with unit tests

PL/SQL vs PL/pgSQL Mapping

Oracle PL/SQL → PostgreSQL PL/pgSQL

-- ORACLE PL/SQL
CREATE OR REPLACE PROCEDURE get_emp(
  p_id   IN  NUMBER,
  p_name OUT VARCHAR2
) IS
BEGIN
  SELECT ename INTO p_name
  FROM   emp
  WHERE  empno = p_id;
  DBMS_OUTPUT.PUT_LINE(p_name);
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    p_name := 'NOT FOUND';
END;

-- POSTGRESQL PL/pgSQL EQUIVALENT
CREATE OR REPLACE FUNCTION get_emp(
  p_id BIGINT
) RETURNS TEXT
LANGUAGE plpgsql AS $$
DECLARE
  v_name TEXT;
BEGIN
  SELECT ename INTO v_name
  FROM   emp
  WHERE  empno = p_id;
  IF NOT FOUND THEN
    RETURN 'NOT FOUND';
  END IF;
  RAISE NOTICE '%', v_name;
  RETURN v_name;
END;
$$;

🔴

Oracle Packages

No direct equivalent. Split into schemas + functions. Package state (global variables) needs rethinking.

⚡

BULK COLLECT

Replace with set-based SQL. PG processes sets natively — row-by-row loops in PL/pgSQL are slow.

Phase 04 · Initial Data Load

Initial Data Load — FDW / DMS

Bulk Transfer

Step-by-Step Process

01Disable triggers and foreign key constraints on target for load speed
02Drop indexes on target tables before loading (recreate after load)
03Export data from Oracle using ora2pg --type COPY or Oracle Data Pump
04Use COPY command for fast bulk load into PostgreSQL (10x faster than INSERT)
05For large tables (>1TB): use AWS DMS full-load or oracle_fdw parallel fetch
06Load large tables in parallel — split by partition key or ROWID range
07Re-enable constraints, rebuild indexes (use REINDEX CONCURRENTLY)
08Run VACUUM ANALYZE on all loaded tables to update statistics

FDW Initial Load Script

oracle_fdw — Direct Oracle → PostgreSQL Transfer

-- Install oracle_fdw extension
CREATE EXTENSION oracle_fdw;

-- Create foreign server pointing to Oracle
CREATE SERVER oracle_src
  FOREIGN DATA WRAPPER oracle_fdw
  OPTIONS (dbserver '//oracle-host:1521/ORCL');

CREATE USER MAPPING FOR postgres
  SERVER oracle_src
  OPTIONS (user 'oracle_user', password 'secret');

-- Import Oracle table as foreign table
IMPORT FOREIGN SCHEMA "APP_OWNER"
  FROM SERVER oracle_src
  INTO oracle_staging;

-- Transfer data directly (no intermediate files!)
INSERT INTO customers
SELECT * FROM oracle_staging.customers;

-- For large tables: parallel load with ranges
-- Split into parallel psql sessions by ID range
INSERT INTO orders
SELECT * FROM oracle_staging.orders
WHERE  order_id BETWEEN 1 AND 5000000;

Load Strategy Comparison

Method	Speed	Best For
oracle_fdw INSERT...SELECT	Medium	Direct transfer, small-medium tables
ora2pg COPY format	Fast	Any size, file-based
AWS DMS Full Load	Very Fast	AWS-hosted environments
Oracle Data Pump + pg_restore	Medium	Air-gapped networks
pgloader	Fast	Parallel, self-contained

Performance Tuning

PostgreSQL — optimize for bulk load

-- Temporarily increase for load speed
SET maintenance_work_mem = '4GB';
SET max_wal_size = '8GB';

-- Disable WAL logging for initial load (unlogged)
ALTER TABLE big_table SET UNLOGGED;
-- Load data here...
ALTER TABLE big_table SET LOGGED;

-- After load: update statistics
VACUUM ANALYZE customers;
VACUUM ANALYZE orders;

Phase 05 · Change Data Capture

CDC — Change Data Capture

Zero Downtime Key

Step-by-Step Process

01Enable Oracle Supplemental Logging for all migrated tables
02Configure Debezium Oracle connector or AWS DMS CDC task pointing to Oracle LogMiner
03Start CDC AFTER initial load completes — capture all changes from load start SCN
04CDC events stream through Kafka topic (Debezium) or DMS replication instance
05Apply changes to PostgreSQL target: INSERT/UPDATE/DELETE replayed in order
06Monitor replication lag — target must stay within 30 seconds of source
07Run side-by-side validation queries on both databases to verify consistency
08Keep CDC running until cutover day — then flush final changes and switch

Debezium CDC Configuration

Debezium Oracle Connector Config (JSON)

{
  "name": "oracle-migration-cdc",
  "connector.class":
    "io.debezium.connector.oracle.OracleConnector",
  "database.hostname": "oracle-host",
  "database.port": "1521",
  "database.dbname": "ORCL",
  "database.user": "logminer_user",
  "table.include.list":
    "APP.CUSTOMERS,APP.ORDERS,APP.PRODUCTS",
  "snapshot.mode": "schema_only",
  // ^ Use schema_only since initial load done via FDW
  "log.mining.strategy": "online_catalog",
  "database.history.kafka.bootstrap.servers":
    "kafka:9092"
}

CDC Tools Comparison

Tool	Transport	Latency
Debezium	Kafka topics	< 1 second
AWS DMS	DMS replication	Seconds
GoldenGate	Direct / Kafka	Sub-second
pglogical	Logical replication	Sub-second
Striim	Streaming	Sub-second

Oracle Prerequisites

Oracle — Enable supplemental logging

-- Enable at database level
ALTER DATABASE ADD
  SUPPLEMENTAL LOG DATA;

-- Enable for all columns on migrated tables
ALTER TABLE app.customers
  ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;

-- Create LogMiner user for Debezium
CREATE USER logminer_user
  IDENTIFIED BY 'secure_pass';
GRANT LOGMINING TO logminer_user;
GRANT SELECT ON V_$DATABASE TO logminer_user;
GRANT SELECT ON V_$LOG TO logminer_user;

Phase 06 · Data Transformation

Data Transformation

Quality Gate

Step-by-Step Process

01Convert Oracle DATE columns (with time) to TIMESTAMP in PostgreSQL
02Transform CHAR(n) trailing spaces to trimmed TEXT values
03Convert RAW/BLOB binary data to BYTEA format using encode/decode
04Reformat NUMBER(1,0) boolean columns to PostgreSQL BOOLEAN
05Handle NULL semantics — Oracle treats '' as NULL; PostgreSQL does not
06Normalise character encoding — ensure UTF-8 consistency throughout
07Transform NLS date format strings to PostgreSQL to_char format codes

Transformation Queries

PostgreSQL — Common transformation fixes

-- Fix empty string vs NULL (Oracle vs PG difference)
UPDATE customers
SET    middle_name = NULL
WHERE  middle_name = '';

-- Convert NUMBER(1) 0/1 to BOOLEAN
ALTER TABLE users
  ADD COLUMN is_active_bool BOOLEAN;
UPDATE users
  SET is_active_bool = (is_active = 1);
ALTER TABLE users DROP COLUMN is_active;
ALTER TABLE users
  RENAME is_active_bool TO is_active;

-- Trim CHAR(n) trailing spaces
UPDATE products
SET    category = RTRIM(category)
WHERE  category <> RTRIM(category);

Critical Differences to Handle

🔴

Empty String = NULL

Oracle: INSERT '' stores NULL. PostgreSQL: '' is an empty string. All empty string → NULL conversions must be explicit.

📅

Oracle DATE has TIME

Oracle DATE = date + time. PostgreSQL DATE = date only. Always map Oracle DATE to PostgreSQL TIMESTAMP.

🔤

CHAR Padding

Oracle CHAR(10) pads with spaces. PostgreSQL CHAR(10) also pads. But comparisons may differ. Use TEXT and TRIM.

✅

NLS Settings

Oracle NLS_DATE_FORMAT affects implicit date conversions. PostgreSQL uses DateStyle. Set explicitly in session or config.

Phase 07 · Data Validation

Data Validation

Go/No-Go Gate

Step-by-Step Process

01Row count validation — every table must match exactly between Oracle and PostgreSQL
02Checksum validation — hash aggregate of key columns to detect data corruption
03Business rule validation — run critical business queries on both DBs, compare results
04Referential integrity check — all FK relationships still hold after migration
05Run application regression test suite against PostgreSQL target
06Performance baseline — top 50 critical queries must run within 110% of Oracle time
07UAT (User Acceptance Testing) — business stakeholders validate key reports and workflows
08Sign-off document from all teams before scheduling cutover

Validation Scripts

Row count + checksum validation

-- Oracle: generate row counts
SELECT table_name,
       num_rows -- from stats
FROM   dba_tables
WHERE  owner = 'APP_OWNER'
ORDER BY table_name;

-- PostgreSQL: match row counts
SELECT schemaname, tablename,
       n_live_tup AS est_rows,
       pg_size_pretty(
         pg_total_relation_size(schemaname||'.'||tablename)
       ) AS size
FROM   pg_stat_user_tables
ORDER BY n_live_tup DESC;

-- Exact count comparison query (both DBs)
SELECT
  (SELECT COUNT(*) FROM oracle_staging.customers) AS oracle_cnt,
  (SELECT COUNT(*) FROM customers)                AS pg_cnt,
  (SELECT COUNT(*) FROM oracle_staging.customers)
    - (SELECT COUNT(*) FROM customers)            AS difference;

🚨

STOP if Count Mismatch

ANY row count mismatch must be investigated and resolved before cutover. Zero tolerance for data loss.

📋

Validation Report

Generate a signed validation report. Business, DBA, and Dev leads must sign off before go-live is approved.

Phase 08 · Cutover & Go-Live

Cutover & Go-Live

D-Day

Cutover Runbook — Step by Step

01Schedule maintenance window (even for zero-downtime: plan a 15-min rollback window)
02Freeze application — put app into read-only mode or enable maintenance page
03Wait for CDC lag to reach ZERO — confirm PostgreSQL is 100% caught up
04Run final row count validation across all critical tables
05Stop CDC / Debezium connector — no more changes from Oracle
06Update connection pool / application config to point to PostgreSQL
07Update DNS or load balancer endpoint to PostgreSQL cluster
08Remove maintenance page — release application traffic to PostgreSQL
09Monitor: query performance, error rates, connection counts for 4 hours
10Keep Oracle in READ-ONLY for 48 hours as fallback. Then decommission.

Cutover Strategies

Strategy	Downtime	Risk
Blue-Green Switch	~5 minutes	Low — instant rollback
DNS Cutover	~0 (TTL-based)	Medium — TTL delay
Connection Pool Redirect	Zero	Low — pgBouncer target switch
Feature Flag Rollout	Zero	Very Low — gradual traffic shift

Rollback Plan

Rollback — Switch back to Oracle

-- If rollback needed within 48h of cutover:

-- Step 1: Re-enable Oracle as write target
-- Step 2: Reverse CDC: PostgreSQL → Oracle
--         (Use pglogical or custom triggers)
-- Step 3: Update connection string back to Oracle
-- Step 4: Investigate root cause
-- Step 5: Fix and re-attempt cutover

-- PostgreSQL: check if system is healthy
SELECT count(*), state
FROM   pg_stat_activity
WHERE  datname = current_database()
GROUP BY state;

-- Monitor error rate after cutover
SELECT query, calls, mean_exec_time, stddev_exec_time
FROM   pg_stat_statements
WHERE  mean_exec_time > 1000  -- queries > 1 second
ORDER BY mean_exec_time DESC
LIMIT 20;

Migration Timeline — Typical Schedule

Timeline varies by database size and complexity score

Week 1–2

Assessment

Ora2Pg assessment run
Object inventory
AWR analysis
Team formation
Target env setup

Week 3–4

Schema & Code

DDL conversion
PL/SQL → PL/pgSQL
Package decomposition
Jobs → pg_cron
Dev env testing

Week 5–6

Initial Load

FDW / DMS setup
Full data transfer
Index rebuild
VACUUM ANALYZE
First count check

Week 7–8

CDC & Testing

Debezium CDC live
Regression testing
Performance tuning
UAT round 1
Lag monitoring

Week 9–10

Validation

Full row counts
Checksum validation
Business UAT
Perf benchmarks
Sign-off obtained

Week 11

Cutover

Final rehearsal
Maintenance window
DNS/pool switch
4-hour monitoring
Oracle standby 48h

Key Considerations

Critical factors that determine migration success

📊

Schema Design Differences

PostgreSQL and Oracle handle schema objects differently. Plan for each of these conversions during design phase.

Oracle PACKAGES → PostgreSQL schemas + grouped functions
Oracle SYNONYMS → search_path or views
Oracle DATABASE LINKS → postgres_fdw extension
Oracle ROWID → PostgreSQL ctid (not recommended for app use)
Oracle GLOBAL TEMP TABLE → PostgreSQL temp tables (different scope)

⚡

Performance Tuning After Migration

PostgreSQL's query planner differs from Oracle CBO. Queries that were fast in Oracle may need index or query tuning.

Run VACUUM ANALYZE immediately after data load
Review top 50 AWR queries — recreate execution plans
Set work_mem per query type (joins, sorts)
Use pg_stat_statements to find slow queries post-migration
Tune shared_buffers (25% RAM), effective_cache_size (75% RAM)

🔄

Transaction & Locking Differences

PostgreSQL uses MVCC — readers never block writers. But locking semantics differ in important ways.

Oracle READ COMMITTED ≈ PostgreSQL READ COMMITTED (similar)
Oracle uses row-level locking; PG uses page-level for some ops
PostgreSQL DDL (ALTER TABLE) takes AccessExclusiveLock — plan carefully
Use SKIP LOCKED for queue-style applications
Dead tuples accumulate — autovacuum must be properly configured

🔒

Security & Authentication

Map Oracle user/role model to PostgreSQL's role-based access control system.

Oracle PROFILE → PostgreSQL pg_hba.conf + scram-sha-256
Oracle VPD (Row-Level Security) → PostgreSQL RLS policies
Oracle Fine-Grained Auditing → pgaudit extension
Oracle Transparent Data Encryption → PostgreSQL TDE (pg_tde ext) or filesystem encryption
Map Oracle CONNECT role to PostgreSQL LOGIN privilege

✅

Data Validation Strategy

Never skip data validation. A systematic approach ensures zero data loss and business continuity.

Level 1: Row counts per table (automated, every 6 hours during CDC)
Level 2: Checksum on key columns (MD5 aggregate comparison)
Level 3: Business rule validation (report outputs match exactly)
Level 4: Application regression test suite (>95% pass rate required)
Level 5: UAT sign-off by business stakeholders

🛠️

Essential PostgreSQL Extensions

Install these extensions immediately after setting up the target PostgreSQL instance.

oracle_fdw — connect to Oracle during migration and for FDW
pg_cron — replace Oracle DBMS_SCHEDULER jobs
pgaudit — audit logging for compliance (replaces Oracle FGA)
pg_stat_statements — query performance monitoring
pg_partman — automatic partition management
PostGIS — if Oracle SDO_GEOMETRY spatial data exists

🚨

High-Risk Conversion Items

These Oracle features require the most manual effort and testing. Allocate 3x more time than expected.

CONNECT BY PRIOR → WITH RECURSIVE (complex rewrites)
Oracle PACKAGES with package-level variables (state)
BULK COLLECT / FORALL bulk operations
Oracle-specific analytic functions (FIRST_VALUE IGNORE NULLS etc.)
Oracle MERGE statement → PostgreSQL INSERT ON CONFLICT
DBMS_CRYPTO / UTL_FILE / UTL_HTTP → extension alternatives

📋

Rollback & Contingency Planning

Always have a tested rollback plan. The ability to roll back gives confidence to proceed with cutover.

Keep Oracle in READ-ONLY for minimum 48 hours post-cutover
Define clear rollback triggers: error rate >5%, response time >3x baseline
Test rollback procedure in full rehearsal before real cutover
Reverse CDC capability: PostgreSQL → Oracle (for data written post-cutover)
Maintain application dual-write capability for first 24 hours if possible

Oracle → PostgreSQL Object Mapping

Complete reference for every Oracle object type

Oracle Object	PostgreSQL Equivalent	Effort & Notes
TABLE	TABLE	Low — Ora2Pg auto-converts types
INDEX	INDEX (B-Tree / GIN / GiST)	Low — same concept, different type options
SEQUENCE	SEQUENCE / IDENTITY column	Low — GENERATED ALWAYS AS IDENTITY preferred
VIEW	VIEW	Low — mostly auto-converts
MVIEW	MATERIALIZED VIEW	Medium — refresh syntax differs slightly
PROCEDURE	FUNCTION (PL/pgSQL)	Medium — syntax differences, no PRAGMA
FUNCTION	FUNCTION (PL/pgSQL)	Medium — RETURN vs RETURNS keyword
PACKAGE	SCHEMA + grouped FUNCTIONs	High — no direct equivalent; package state lost
TRIGGER	TRIGGER + FUNCTION	Medium — PG triggers call a separate function
SYNONYM	search_path / VIEW / ALTER TABLE SET SCHEMA	Medium — per use-case
DATABASE LINK	postgres_fdw FOREIGN SERVER	Medium — FDW setup required
PARTITION (RANGE/LIST)	Declarative PARTITION BY RANGE/LIST	Medium — syntax different, INTERVAL → pg_partman
DBMS_SCHEDULER JOB	pg_cron extension	Medium — cron syntax, different approach
DBMS_OUTPUT	RAISE NOTICE / RAISE LOG	Low — simple replacement
CONNECT BY PRIOR	WITH RECURSIVE CTE	High — complete query rewrite needed
ROWNUM	LIMIT / ROW_NUMBER() OVER()	Medium — pattern-specific rewrite
DECODE()	CASE WHEN ... THEN ... END	Low — straightforward replacement
NVL(a,b)	COALESCE(a,b)	Low — direct replacement
SYSDATE	NOW() / CURRENT_TIMESTAMP	Low — direct replacement
SUBSTR(s,1,n)	SUBSTRING(s,1,n) or SUBSTR(s,1,n)	Low — PostgreSQL supports both
TO_CHAR(date,'fmt')	TO_CHAR(date,'fmt') — format codes differ	Medium — format string differences (MM vs MM is same, but MI vs MM for minutes)
MERGE INTO	INSERT ... ON CONFLICT DO UPDATE	Medium — syntax completely different
BULK COLLECT / FORALL	Set-based SQL / UNNEST()	High — redesign as set operations
VPD (Fine-Grained Security)	Row-Level Security (RLS)	Medium — different implementation approach
Oracle Text (Full-Text)	tsvector / tsquery / GIN index	Medium — native PG full-text search

Migration Checklist

Click each item to mark as complete — track your progress

✦ Pre-Migration

✓

Ora2Pg assessment completed — migration score documented

✓

All Oracle objects inventoried (tables, procs, packages, triggers)

✓

AWR top 50 SQL captured and reviewed

✓

Target PostgreSQL instance provisioned and configured

✓

Extensions installed: oracle_fdw, pg_cron, pgaudit, pg_stat_statements

✓

Migration team identified and roles assigned

✓

Rollback plan documented and tested

✓

Cutover strategy agreed (Blue-Green / DNS / Pool)

✓

Oracle supplemental logging enabled

✓

Schema conversion completed and tested on DEV environment

✓

PL/SQL → PL/pgSQL conversion done and unit tested

✓

pg_hba.conf and postgresql.conf tuned for production load

✦ Migration & Go-Live

✓

Initial full data load completed successfully

✓

All indexes rebuilt and VACUUM ANALYZE run on all tables

✓

CDC / Debezium running — lag monitored < 30 seconds

✓

Row count validation passed for ALL tables

✓

Checksum validation passed for all critical tables

✓

Application regression test suite: >95% pass rate

✓

UAT completed — business stakeholders signed off

✓

Performance benchmarks within 110% of Oracle baseline

✓

Cutover rehearsal completed — timed and documented

✓

Cutover executed — app traffic on PostgreSQL

✓

4-hour post-cutover monitoring completed — no critical issues

✓

Oracle kept in READ-ONLY for 48h then decommissioned

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Saturday, July 11, 2026

Oracle → PostgreSQL Migration Complete Architecture Guide (Step-by-Step) Complete Guide for DBAs 🔥

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Oracle → PostgreSQL Migration Complete Architecture Guide (Step-by-Step) Complete Guide for DBAs 🔥

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Oracle → PostgreSQL
Migration Architecture