PolarDB:Decoderbufs

• Decoderbufs is supported on the PolarDB for PostgreSQL (Compatible with Oracle) clusters that run the following engines:

  • PolarDB for PostgreSQL (Compatible with Oracle) 2.0 (revision version 2.0.14.1.0 or later)

  Note

  You can execute the following statements to view the revision version of a PolarDB for PostgreSQL (Compatible with Oracle) cluster:

  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.

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';

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

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.

You can configure logical replication in the postgresql.conf file.

# MODULES
shared_preload_libraries = 'decoderbufs'

# REPLICATION
wal_level = logical             # minimal, archive, hot_standby, or logical (change requires restart)
max_wal_senders = 8             # max number of walsender processes (change requires restart)
wal_keep_segments = 4           # in logfile segments, 16MB each; 0 disables
#wal_sender_timeout = 60s       # in milliseconds; 0 disables
max_replication_slots = 4       # max number of replication slots (change requires restart)

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';

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