Postgres Decoderbufs

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

Thanks to

• The original Decoderbufs Project on which this is based
• The PostgreSQL Team for adding logical decoding support

Dependencies

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

Building

postgres-decoderbufs has to be built from source after installing required dependencies. The required dependencies are first PostgreSQL (for pg_config), PostgreSQL server development packages, protobuf-c for the Protocol Buffer support and some PostGIS development packages.

Installing Dependencies

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

When updating the ProtoBuf definition, also install the ProtoBuf C compiler:

apt-get install -y protobuf-c-compiler=1.2.*

The above are taken from the Debezium container 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

Getting the source code

If you have all of the above prerequisites installed, clone this git repo to build from source:

git clone https://github.com/debezium/postgres-decoderbufs.git
cd postgres-decoderbufs

Optional: Re-generating ProtoBuf code

This is only needed after changes to the ProtoBuf definition (_proto/pg_logicaldec.proto):

cd proto
protoc-c --c_out=../src/proto pg_logicaldec.proto
cd ..

Commit the generated files to git then.

Building and installing decoderbufs

If you have multiple Postgres versions installed, you can select which version to install decoderbufs into by altering your $PATH to point to the right version. Then make and make install for each version. Here is an example:

# Install for Postgres 9.6 if I have multiple local versions
export PATH=/usr/lib/postgresql/9.6/bin:$PATH
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