A PostgreSQL logical decoder output plugin to deliver data as Protocol Buffers, adapted for Debezium
- The original Decoderbufs Project on which this is based
- The PostgreSQL Team for adding logical decoding support
This code depends on the following libraries and requires them for compilation:
- PostgreSQL 9.6+
- Protobuf-c 1.2+ - used for data serialization
- PostGIS 2.1+ - used for Postgres geometric types support
To build you will need to install PostgreSQL (for pg_config), PostgreSQL server development packages, protobuf-c for the Protocol Buffer support and some PostGIS development packages
# Core build utilities
apt-get update && apt-get install -f -y software-properties-common build-essential pkg-config git postgresql-server-dev-9.6
# PostGIS dependency
apt-get install -f -y libproj-dev liblwgeom-dev
# Protobuf-c dependency (requires a non-stable Debian repo)
add-apt-repository "deb http://ftp.debian.org/debian testing main contrib" && apt-get update
apt-get install -y libprotobuf-c-dev=1.2.1-1+b1
The above are taken from the Debezium docker images.
You just need to make sure the above software packages (or some flavour thereof) are installed for your distro.
Note that the last step from the above sequence is only required for Debian to be able to install libprotobuf-c-dev:1.2.1
If you have all of the prerequisites installed you should be able to just:
make && make install
Once the extension has been installed you just need to enable it and logical replication in postgresql.conf:
# 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)
In addition, permissions will have to be added for the user that connects to the DB to be able to replicate. This can be modified in pg_hba.conf like so:
local replication <youruser> trust
host replication <youruser> 127.0.0.1/32 trust
host replication <youruser> ::1/128 trust
And restart PostgreSQL.
-- can use SQL for demo purposes
select * from pg_create_logical_replication_slot('decoderbufs_demo', 'decoderbufs');
-- DO SOME TABLE MODIFICATIONS (see below about UPDATE/DELETE)
-- peek at WAL changes using decoderbufs debug mode for SQL console
select data from pg_logical_slot_peek_changes('decoderbufs_demo', NULL, NULL, 'debug-mode', '1');
-- get WAL changes using decoderbufs to update the WAL position
select data from pg_logical_slot_get_changes('decoderbufs_demo', NULL, NULL, 'debug-mode', '1');
-- check the WAL position of logical replicators
select * from pg_replication_slots where slot_type = 'logical';
If you're performing an UPDATE/DELETE on your table and you don't see results for those operations from logical decoding, make sure you have set REPLICA IDENTITY appropriately for your use case.
The binary format will be consumed by the Debezium Postgres Connector.
The following table shows how current PostgreSQL type OIDs are mapped to which 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 |
File bug reports and feature requests using Debezium's JIRA and the postgresql-connector component