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    PolarDB:decoderbufs

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    PolarDB:decoderbufs

    Last Updated:Oct 27, 2024

    Decoderbufs is a PostgreSQL logical decoder output plug-in for logical replication in the Protocol Buffers format.

    Prerequisites

    • Decoderbufs is supported on the following PolarDB for PostgreSQL clusters:

      • PostgreSQL 14 (revision version 14.5.1.0 or later)

      • PostgreSQL 11 (revision version 1.1.28 or later)

      Note

      You can execute the following statement to view the minor version that is used by PolarDB for PostgreSQL:

      • PostgreSQL 14

        SELECT version();

      • PostgreSQL 11

        SHOW polar_version;

    • Decoderbufs depends on the following libraries:

      • PostgreSQL 9.6 or later

      • Protobuf-c: 1.2 or later for data serialization

      • PostGIS: 2.1 or later to support PostgreSQL Geo type.

    Configuration and usage

    Decoderbufs is automatically loaded by default. You must modify the wal_level parameter to logical.

    Note

    This parameter can be modified in the console. For more information, see Procedure. The cluster restarts after you modify the parameter. Proceed with caution.

    Examples for logical replication:

    1. Create a logical replication slot and set the codec plug-in to decoderbufs. 

      SELECT * FROM pg_create_logical_replication_slot('decoderbufs_demo', 'decoderbufs');

    2. Modify the published table.

    3. View WAL logs by using decoderbufs debug mode. 

      SELECT data FROM pg_logical_slot_peek_changes('decoderbufs_demo', NULL, NULL, 'debug-mode', '1');

    4. Obtain WAL changes by using decoderbufs to update the WAL position. 

      SELECT data FROM pg_logical_slot_get_changes('decoderbufs_demo', NULL, NULL, 'debug-mode', '1');

    5. Check the WAL position of logical replicators. 

      SELECT * FROM pg_replication_slots WHERE slot_type = 'logical';

    Data type mappings

    The following table lists how current PostgreSQL type OIDs are mapped to decoderbuf fields.

    PostgreSQL type OID

    Decoderbuf field

    BOOLOID

    datum_boolean

    INT2OID

    datum_int32

    INT4OID

    datum_int32

    INT8OID

    datum_int64

    OIDOID

    datum_int64

    FLOAT4OID

    datum_float

    FLOAT8OID

    datum_double

    NUMERICOID

    datum_double

    CHAROID

    datum_string

    VARCHAROID

    datum_string

    BPCHAROID

    datum_string

    TEXTOID

    datum_string

    JSONOID

    datum_string

    XMLOID

    datum_string

    UUIDOID

    datum_string

    TIMESTAMPOID

    datum_string

    TIMESTAMPTZOID

    datum_string

    BYTEAOID

    datum_bytes

    POINTOID

    datum_point

    PostGIS geometry

    datum_point

    PostGIS geography

    datum_point