PostgreSQL’s COPY command in-depth analysis

PostgreSQL's COPY command

PostgreSQL's COPY command is a core tool for efficient data import and export, and its performance is far beyond conventional INSERT statements. The following is a deep analysis of the COPY command:

A COPY command basics

1.1 Basic syntax comparison

Command Type	Syntax example	Execution location	File access permissions
Server side COPY	`COPY table FROM '/path/';`	Database Server	Requires user permissions for postgres system
Client COPY	`\copy table FROM '';`	Client Machine	Use client user permissions

1.2 Core Function Matrix

Function	COPY FROM	COPY TO
Data loading speed	Ten thousand rows per second	Ten thousand rows per second
Transaction processing	Single transaction operation	Single transaction operation
Binary support	yes	yes
Error handling	Skip the error line	-

2 Advanced usage skills

2.1 Complex data conversion

-- Convert data types when importing
COPY users(id, name, reg_date) 
FROM '/data/' 
WITH (FORMAT csv, HEADER,
      DELIMITER '|',
      NULL 'NULL',
      FORCE_NOT_NULL (id, name),
      ENCODING 'UTF8');

2.2 Conditional Export

-- Export query results
COPY (SELECT * FROM orders WHERE order_date &gt; '2025-01-01') 
TO '/data/recent_orders.csv' 
WITH (FORMAT csv, HEADER);

Three Performance Optimization Solution

3.1 Batch Loading Best Practices

# Use parallel loading (after splitting the file)for i in {1..4}; do
  psql -c "COPY large_table FROM '/data/part$' WITH (FORMAT csv)" &amp;
done
wait

3.2 Key performance parameters

parameter	Recommended value	Influence
`maintenance_work_mem`	1GB+	Improve import sorting efficiency
`max_wal_size`	4GB+	Reduce WAL checkpoints
`synchronous_commit`	off	Disable synchronous submission speed up import

Four Exception handling mechanism

4.1 Error logging

-- Create an error log table
CREATE TABLE import_errors (
    line_num integer,
    error_msg text,
    raw_data text
);
-- Import with error records
BEGIN;
CREATE TEMP TABLE temp_import (LIKE target_table);
COPY temp_import FROM '/data/' 
  WITH (FORMAT csv, HEADER);
INSERT INTO target_table
  SELECT * FROM temp_import
  ON CONFLICT DO NOTHING;
INSERT INTO import_errors
  SELECT pg_copy_log();
COMMIT;

4.2 Binary format processing

# Export binary datapg_dump -t table_name -Fc -f  dbname
# Binary file conversionpg_restore -l  &gt;

5. Monitoring and Maintenance

5.1 Performance monitoring query

-- CheckCOPYOperation history
SELECT query, duration 
FROM pg_stat_statements 
WHERE query LIKE 'COPY%' 
ORDER BY duration DESC;
-- Check the import progress（PostgreSQL 14+）
SELECT pid, query, pg_stat_get_progress_info('COPY') 
FROM pg_stat_activity 
WHERE backend_type = 'client backend';

5.2 Maintenance suggestions

Regularly clean temporary files: COPY operation may generate a large number of WAL logs
Version upgrade verification: COPY behavior may differ in different PostgreSQL versions
Network optimization: Consider compression options when transferring across data centers

The COPY command is the core tool for PostgreSQL data migration. Mastering its advanced usage can significantly improve ETL efficiency. For TB-level data migration, it is recommended:

Reduce I/O with binary format
Parallel loading in combination with table partitions
Disable WAL archive in the maintenance window
Consider using pg_bulkload extension to process hyperscale data

For more details, please check the official documentation:

/docs/17/

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