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AWS S3

AWS S3 is an object storage service offering industry-leading scalability, data availability, security, and performance. It is read-only and supports below file formats:

The S3 Wrapper allows you to read data of below formats from S3 within your Postgres database.

  1. CSV - with or without header line
  2. JSON Lines
  3. Parquet

The S3 Wrapper also supports below compression algorithms:

  1. gzip
  2. bzip2
  3. xz
  4. zlib

Note for CSV and JSONL files: currently all columns in S3 files must be defined in the foreign table and their types must be text type.

Note for Parquet files: the whole Parquet file will be loaded into local memory if it is compressed, so keep the file size as small as possible.

Preparation

Before you can query S3, you need to enable the Wrappers extension and store your credentials in Postgres.

Enable Wrappers

Make sure the wrappers extension is installed on your database:

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create extension if not exists wrappers with schema extensions;

Enable the S3 Wrapper

Enable the s3_wrapper FDW:

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create foreign data wrapper s3_wrapper
  handler s3_fdw_handler
  validator s3_fdw_validator;

Store your credentials (optional)

By default, Postgres stores FDW credentials inside pg_catalog.pg_foreign_server in plain text. Anyone with access to this table will be able to view these credentials. Wrappers is designed to work with Vault, which provides an additional level of security for storing credentials. We recommend using Vault to store your credentials.

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-- Save your AWS credential in Vault and retrieve the `key_id`
insert into vault.secrets (name, secret)
values (
  'vault_access_key_id',
  '<access key id>'
)
returning key_id;

insert into vault.secrets (name, secret)
values (
  'vault_secret_access_key',
  '<secret access key>'
)
returning key_id;

Connecting to S3

We need to provide Postgres with the credentials to connect to S3, and any additional options. We can do this using the create server command:

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create server s3_server
  foreign data wrapper s3_wrapper
  options (
    vault_access_key_id '<your vault_access_key_id from above>',
    vault_secret_access_key '<your vault_secret_access_key from above>',
    aws_region 'us-east-1'
  );

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create server s3_server
  foreign data wrapper s3_wrapper
  options (
    aws_access_key_id 'your_aws_access_key_id',
    aws_secret_access_key 'your_aws_secret_access_key',
    aws_region 'us-east-1'
  );

The full list of options are below:

  • aws_access_key_id (required) - Your access key
  • aws_secret_access_key (required) - Your secret key
  • aws_region (required) - The region of your bucket (if providing an endpoint URL with a region in it, make sure that they are the same)
  • endpoint_url (optional) - An optional URL to allow connection to S3-compliant providers (i.e. Wasabi, Cloudflare R2, Backblaze B2, DigitalOcean Spaces)
  • path_style_url (optional) - Whether to use path-style URL access. This is required by some S3-compliant providers. true or false, default is false.

Required S3 permissions

Below S3 permissions are needed:

  • s3:GetObject
  • s3:GetObjectAttributes

If the bucket is versioned, we also need:

  • s3:GetObjectVersion
  • s3:GetObjectVersionAttributes

Connecting to S3-compliant Providers - Supabase Storage

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create server s3_server
  foreign data wrapper s3_wrapper
  options (
    aws_access_key_id '<supabase_storage_access_key>',
    aws_secret_access_key '<supabase_storage_secret_key>',
    aws_region 'eu-central-1',
    endpoint_url 'https://<project_ref>.supabase.co/storage/v1/s3',
    path_style_url 'true'
  );

Connecting to S3-compliant Providers - Wasabi

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create server s3_server
  foreign data wrapper s3_wrapper
  options (
    aws_access_key_id '<your_wasabi_access_key>',
    aws_secret_access_key '<your_wasabi_secret_key>',
    aws_region 'eu-central-1',
    endpoint_url 'https://s3.eu-central-1.wasabisys.com'
  );

Create a schema

We recommend creating a schema to hold all the foreign tables:

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create schema if not exists s3;

Options

The following options are available when creating S3 foreign tables:

  • uri - S3 URI, required. For example, s3://bucket/s3_table.csv
  • format - File format, required. csv, jsonl, or parquet
  • has_header - If the CSV file has header, optional. true or false, default is false
  • compress - Compression algorithm, optional. One of gzip, bzip2, xz, zlib, default is no compression

Entities

CSV Files

This is an object representing CSV files in S3.

Ref: AWS S3 docs

Operations

Object Select Insert Update Delete Truncate
CSV ✅ ❌ ❌ ❌ ❌

Usage

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create foreign table s3.table_csv (
  name text,
  sex text,
  age text,
  height text,
  weight text
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.csv',
    format 'csv',
    has_header 'true'
  );

Notes

  • All columns must be defined in the foreign table
  • All column types must be text
  • Optional header support via has_header option
  • Supports compression (gzip, bzip2, xz, zlib)

JSON Lines Files

This is an object representing JSONL files in S3.

Ref: JSONL docs

Operations

Object Select Insert Update Delete Truncate
JSONL ✅ ❌ ❌ ❌ ❌

Usage

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create foreign table s3.table_jsonl (
  name text,
  sex text,
  age text,
  height text,
  weight text
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.jsonl',
    format 'jsonl'
  );

Notes

  • All columns must be defined in the foreign table
  • All column types must be text
  • Each line must be a valid JSON object
  • Supports compression (gzip, bzip2, xz, zlib)

Parquet Files

This is an object representing Parquet files in S3.

Ref: Parquet docs

Operations

Object Select Insert Update Delete Truncate
Parquet ✅ ❌ ❌ ❌ ❌

Usage

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create foreign table s3.table_parquet (
  id integer,
  bool_col boolean,
  bigint_col bigint,
  float_col real,
  date_string_col text,
  timestamp_col timestamp
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.parquet',
    format 'parquet'
  );

Notes

  • Not all columns need to be defined in foreign table
  • Column names must match between Parquet file and foreign table
  • Supports various Postgres data types (see Data Types section)
  • Compressed files are loaded entirely into memory
  • Supports compression (gzip, bzip2, xz, zlib)

Query Pushdown Support

This FDW doesn't support query pushdown.

Supported Data Types For Parquet File

The S3 Wrapper uses Parquet file data types from arrow_array::types, below are their mappings to Postgres data types.

Postgres Type Parquet Type
boolean BooleanType
char Int8Type
smallint Int16Type
real Float32Type
integer Int32Type
double precision Float64Type
bigint Int64Type
numeric Float64Type
text ByteArrayType
date Date64Type
timestamp TimestampNanosecondType
timestamptz TimestampNanosecondType

Limitations

This section describes important limitations and considerations when using this FDW:

  • Large result sets experience slower performance due to full data transfer requirement
  • Compressed files are loaded entirely into memory and have additional processing overhead
  • CSV and JSONL columns must be defined as text type only
  • All columns must be defined in foreign tables for CSV and JSONL
  • Column names must match exactly for Parquet files
  • No support for S3 Select or other S3-side filtering
  • Materialized views using these foreign tables may fail during logical backups

Examples

Basic Example

This will create some "foreign table" inside your Postgres database can read data from S3:

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-- CSV file, no compression
create foreign table s3.table_csv (
  name text,
  sex text,
  age text,
  height text,
  weight text
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.csv',
    format 'csv',
    has_header 'true'
  );

-- JSON line file, no compression
create foreign table s3.table_jsonl (
  name text,
  sex text,
  age text,
  height text,
  weight text
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.jsonl',
    format 'jsonl'
  );

-- GZIP compressed CSV file
create foreign table s3.table_csv_gzip (
  name text,
  sex text,
  age text,
  height text,
  weight text
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.csv.gz',
    format 'csv',
    has_header 'true',
    compress 'gzip'
  );

-- Parquet file, no compression
create foreign table s3.table_parquet (
  id integer,
  bool_col boolean,
  bigint_col bigint,
  float_col real,
  date_string_col text,
  timestamp_col timestamp
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.parquet',
    format 'parquet'
  );

-- GZIP compressed Parquet file
create foreign table s3.table_parquet_gz (
  id integer,
  bool_col boolean,
  bigint_col bigint,
  float_col real,
  date_string_col text,
  timestamp_col timestamp
)
  server s3_server
  options (
    uri 's3://bucket/s3_table.parquet.gz',
    format 'parquet',
    compress 'gzip'
  );

Read from Supabase Storage

This example will read a CSV file stored on Supabase Storage. The access information can be found on Supabase Storage settings page.

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create server s3_server
  foreign data wrapper s3_wrapper
  options (
    aws_access_key_id '<access key ID>',
    aws_secret_access_key '<secret access key>',
    aws_region '<region>',
    endpoint_url 'https://<project_ref>.supabase.co/storage/v1/s3',
    path_style_url 'true'
  );

create foreign table s3.supabase_table_csv (
  id text,
  name text
)
  server s3_server
  options (
    uri 's3://mybucket/myfile.csv',
    format 'csv',
    has_header 'true'
  );