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d9477a5 Jan 15, 2018
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Postgres Decoderbufs

A PostgreSQL logical decoder output plugin to deliver data as Protocol Buffers, adapted for Debezium

Thanks to

Dependencies

This code depends on the following libraries and requires them for compilation:

Building

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

Debian

# 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.

Other Linux distributions

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.

Usage

-- 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.

Type Mappings

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

Support

File bug reports and feature requests using Debezium's JIRA and the postgresql-connector component