How to Migrate from Clickhouse to Oracle in PostgreSQL

Galaxy Glossary

How do I migrate data from ClickHouse to Oracle without downtime?

Step-by-step process to export data from ClickHouse and import it into Oracle with minimal downtime.

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Description

Example H2

Example H3

Why move data from ClickHouse to Oracle?

Oracle offers mature PL/SQL, strong ACID compliance, and rich ecosystem features that some enterprises need for transactional workloads, auditing, or vendor policy.Migrating retains historical analytics from ClickHouse while unlocking Oracle's OLTP strengths.

What are the high-level migration steps?

Typical workflow: 1) analyse ClickHouse schemas, 2) map data types to Oracle, 3) export data (CSV, Parquet, or Avro), 4) create matching tables in Oracle, 5) bulk-load files with SQL*Loader or Data Pump, 6) validate counts/checksums, 7) cut over traffic using DB links or ETL.

How do I export ClickHouse data to CSV?

Run SELECT … INTO OUTFILE for each table.Compress for large volumes.

SELECT *
FROM Customers
INTO OUTFILE '/tmp/customers.csv'
FORMAT CSV;

Repeat for Orders, Products, and OrderItems. Store files where Oracle server can read.

How do I create matching tables in Oracle?

Translate ClickHouse data types.Keep primary keys and indexes minimal until after load.

CREATE TABLE customers (
id NUMBER PRIMARY KEY,
name VARCHAR2(100),
email VARCHAR2(255),
created_at TIMESTAMP
);

Repeat for the Orders, Products, and OrderItems tables.

How do I load CSV files into Oracle with SQL*Loader?

Generate a control file per table.

-- customers.ctl
OPTIONS (SKIP=1)
LOAD DATA
INFILE '/tmp/customers.csv'
INTO TABLE customers
FIELDS TERMINATED BY ','
(id, name, email, created_at "TO_TIMESTAMP(:created_at, 'YYYY-MM-DD HH24:MI:SS')")

Execute:

sqlldr userid=system/password control=customers.ctl parallel=true direct=true

SQL*Loader's direct path and parallel flags speed up bulk import.

How do I migrate online with database links?

To minimise downtime, create an ODBC gateway or Oracle Heterogeneous Services DB link to ClickHouse.Then copy deltas after the bulk load.

CREATE DATABASE LINK ch_link CONNECT TO "ch_user" IDENTIFIED BY "pwd"
USING 'clickhouse_dsn';.

INSERT /*+ APPEND */ INTO orders o
SELECT * FROM orders@ch_link
WHERE order_date > TO_DATE('2023-10-01','YYYY-MM-DD');

Schedule incremental jobs until cut-over.

Best practices for zero-downtime migration?

Freeze ClickHouse writes briefly, load final deltas, switch application connection strings, and monitor lag KPIs. Keep both systems running read-only initially for rollback safety.

Common mistakes and how to avoid them

Data-type mismatch: ClickHouse DateTime64 exceeds Oracle TIMESTAMP precision. Map explicitly or round values.

Loading with constraints enabled: Foreign-key checks slow imports.Disable constraints, load, re-enable and validate.

FAQ

Do I need Oracle GoldenGate?

Not required for small datasets; DB links or ETL suffice. GoldenGate simplifies real-time replication at enterprise scale.

How do I verify migration success?

Compare row counts, run checksums per table, and spot-check critical reports in both systems before decomissioning ClickHouse.

Why How to Migrate from Clickhouse to Oracle in PostgreSQL is important

How to Migrate from Clickhouse to Oracle in PostgreSQL Example Usage


-- Copy new orders made after bulk load
INSERT /*+ APPEND */ INTO orders o
SELECT id, customer_id, order_date, total_amount
FROM orders@ch_link
WHERE order_date > TO_DATE('2023-10-01','YYYY-MM-DD');

How to Migrate from Clickhouse to Oracle in PostgreSQL Syntax


-- 1. Export from ClickHouse
SELECT id, name, email, created_at
FROM Customers
INTO OUTFILE '/tmp/customers.csv'
FORMAT CSV;

-- 2. Oracle DDL
CREATE TABLE customers (
  id         NUMBER PRIMARY KEY,
  name       VARCHAR2(100),
  email      VARCHAR2(255),
  created_at TIMESTAMP
);

-- 3. SQL*Loader control file (customers.ctl)
LOAD DATA
INFILE 'customers.csv'
INTO TABLE customers
FIELDS TERMINATED BY ','
(id, name, email, created_at "TO_TIMESTAMP(:created_at, 'YYYY-MM-DD HH24:MI:SS')");

-- 4. Run loader
sqlldr userid=system/password control=customers.ctl parallel=true direct=true;

-- 5. Incremental sync via DB link
CREATE DATABASE LINK ch_link USING 'clickhouse_dsn';
INSERT INTO customers
SELECT * FROM customers@ch_link
WHERE created_at > TO_DATE('2023-10-01','YYYY-MM-DD');

Common Mistakes

Not mapping ClickHouse DateTime64 to Oracle TIMESTAMP. Fix: cast or truncate to supported precision before export.
Leaving foreign-key constraints enabled during bulk load, causing slow imports. Fix: disable, load, then re-enable.