pgpack 0.1.3.1

PGCopy dump packed into LZ4, ZSTD or uncompressed with meta data information packed into zlib.

PGPack format

Storage format for PGCopy dump packed into LZ4, ZSTD or uncompressed with meta data information packed into zlib

PGPack structure

• header b"PGPACK\n\x00" 8 bytes
• unsigned long integer zlib.crc32 for packed metadata 4 bytes
• unsigned long integer zlib packed metadata length 4 bytes
• zlib packed metadata
• unsigned char compression method 1 byte
• unsigned long long integer packed pgcopy data length 8 bytes
• unsigned long long integer unpacked pgcopy data length 8 bytes
• packed pgcopy data

Installation

From pip

pip install pgpack

From local directory

pip install .

From git

pip install git+https://github.com/0xMihalich/pgpack

Metadata format

Metadata for PGCopy dump contained Column names and OID Types

Decompressed metadata structure

list[
    list[
        column number int,
        list[
            column name str,
            column oid int,
            column lengths int,
            column scale int,
            column nested int,
        ]
    ]
]

Compression methods

• NONE (value = 0x02) PGCopy dump without compression
• LZ4 (value = 0x82) PGCopy dump with lz4 compression
• ZSTD (value = 0x90) PGCopy dump with zstd compression

Get ENUM for set compression method

from pgpack import CompressionMethod

compression_method = CompressionMethod.NONE  # no compression
compression_method = CompressionMethod.LZ4  # lz4 compression (default)
compression_method = CompressionMethod.ZSTD  # zstd compression

Class PGPackReader

Initialization parameters

• fileobj - BufferedReader object (file, BytesIO e t.c)

Methods and attributes

• columns - List columns names
• pgtypes - List PGOid for all columns
• pgparam - List PGParam for all columns
• pgcopy - PGCopy object
• header - b"PGPack\n" 8 bytes
• metadata_crc - integer crc32 sign for metadata_zlib object
• metadata_length - integer length metadata_zlib in bytes
• metadata_zlib - zlib packed metadata in bytes
• compression_method - CompressionMethod object
• pgcopy_compressed_length - integer packed pgcopy data length
• pgcopy_data_length - integer unpacked pgcopy data length
• offset_opener - OffsetOpener object
• pgcopy_compressor - File object for reading uncompressed PGCopy data
• to_bytes() - Method for reading uncompressed PGCopy data as bytes
• to_python() - Method for reading uncompressed PGCopy data as list of python objects
• to_pandas() - Method for reading uncompressed PGCopy data as pandas.DataFrame
• to_polars() - Method for reading uncompressed PGCopy data as polars.DataFrame

Class PGPackWriter

Initialization parameters

• fileobj - BufferedReader object (file, BytesIO e t.c)
• compression_method - CompressionMethod object (default is CompressionMethod.LZ4)

Methods and attributes

• columns - List columns names
• pgtypes - List PGOid for all columns
• pgparam - List PGParam for all columns
• metadata_end - Integer, zlib packed metadata end position
• fileobj_end - Integer, packed pgcopy data end position
• pgcopy_compressed_length - integer packed pgcopy data length
• pgcopy_data_length - integer unpacked pgcopy data length
• write_metadata(metadata) - Make first blocks with metadata. Parameter: metadata as bytes
• write_pgcopy(pgcopy) - Make second blocks with pgcopy. Parameter: pgcopy as BufferedReader
• write(metadata, pgcopy) - Write PGPack file. Parameters: metadata as bytes, pgcopy as BufferedReader
• from_python(dtype_data) - Write PGPack file from python objects. Parameter: dtype_data as python object list
• from_pandas(data_frame) - Write PGPack file from pandas.DataFrame. Parameter: data_frame as pandas.DataFrame
• from_polars(data_frame) - Write PGPack file from polars.DataFrame. Parameter: data_frame as polars.DataFrame

Errors

• PGPackError - Base PGPack error
• PGPackHeaderError - Error header signature
• PGPackMetadataCrcError - Error metadata crc32
• PGPackModeError - Error fileobject mode