How to Migrate from BigQuery to Oracle

Why move data from BigQuery to Oracle?

Teams consolidate analytics and OLTP workloads, cut cloud costs, or join Oracle-only systems. Oracle offers mature ACID transactions, partitioning, and on-prem control.

Which migration paths exist?

Three practical options: 1) CSV/Parquet export + SQL*Loader, 2) BigQuery → Cloud Storage → Oracle External Tables, 3) Oracle Database Gateway for BigQuery with INSERT SELECT over DB Link.

How do I export BigQuery tables efficiently?

Use bq extract with compressed Parquet to Cloud Storage.Parquet preserves data types and is splittable for parallel load.

bq extract --destination_format=PARQUET \
--compression=SNAPPY \
ecommerce.Orders gs://bq_oracle_stage/Orders_*.parquet


How do I create matching Oracle tables?

Map BigQuery types to Oracle equivalents before load. Example: STRING → VARCHAR2, INT64 → NUMBER, TIMESTAMP → TIMESTAMP(6).

CREATE TABLE Orders (
id NUMBER PRIMARY KEY,
customer_id NUMBER REFERENCES Customers(id),
order_date DATE,
total_amount NUMBER(14,2)
);


What is the load command syntax?

SQL*Loader and external tables share a control file syntax.External tables avoid staging into redo logs, saving space.

CREATE TABLE ext_orders
ORGANIZATION EXTERNAL (
TYPE ORACLE_LOADER
DEFAULT DIRECTORY gcs_stage
ACCESS PARAMETERS (
records delimited by newline
preprocessor gcs_parquet
)
LOCATION ('Orders_001.parquet', 'Orders_002.parquet')
)
REJECT LIMIT UNLIMITED;


How do I merge data into live Oracle tables?

Use INSERT APPEND for new tables or MERGE for incremental syncs.

INSERT /*+ APPEND */ INTO Orders SELECT * FROM ext_orders;


Can I migrate in one hop?

Yes.Configure Oracle Database Gateway for BigQuery, create a DB Link, then pull data.

INSERT /*+ PARALLEL(8) */ INTO Orders
SELECT * FROM Orders@BG_LINK;


How do I validate the migration?

Row counts: compare SELECT COUNT(*). Check aggregates like SUM(total_amount).Hash columns for spot checks.

Best practices for large datasets?

Split exports by date, leverage parallel SQL*Loader, disable indexes/constraints during bulk loads, and enable Oracle Direct Path.

Next steps after data load?

Rebuild indexes, gather statistics (DBMS_STATS), recreate views, and port UDFs to PL/SQL.

Common BigQuery-to-Oracle data type mappings

STRING → VARCHAR2(4000), BYTES → RAW, NUMERIC → NUMBER(38,9), BOOL → NUMBER(1), DATE → DATE, STRUCT → JSON.

How to handle partitioned tables?

Create matching Oracle Range or Interval partitions, export each BigQuery partition to its own file, and load in parallel.

Orders partition example

CREATE TABLE Orders (
...
) PARTITION BY RANGE (order_date) (
PARTITION p2023 VALUES LESS THAN (DATE '2024-01-01'),
PARTITION pmax VALUES LESS THAN (MAXVALUE)
);


Automating the workflow?

Wrap export, upload, and load steps in Cloud Build or Airflow, passing file lists to SQL*Loader via templates.

Security considerations?

Encrypt files in transit (gsutil --sse), restrict GCS access, and purge stage files after load.In Oracle, load into staging schema with limited privileges.

Performance tuning tips?

Increase SQL*Loader PARALLEL, use DIRECT=TRUE, and adjust Oracle PGA_AGGREGATE_LIMIT to sustain throughput.

Monitoring progress?

Track Cloud Storage object counters, SQL*Loader log files, and Oracle v$session_longops to estimate time remaining.

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