Python package to read, parse and convert PostgreSQL logical decoding messages to change data capture messages. Built using psycopg2's logical replication support objects, PostgreSQL's pgoutput plugin and Pydantic.
Uses python >= 3.8
Developed on PostgreSQL 12 for now.
Warning: this is a prototype and not production tested
$ pip install pypgoutput- Replication messages are consumed via psycopg2's replication connection. https://www.psycopg.org/docs/extras.html#replication-support-objects
- The binary messages from pgoutput logical decoding are parsed in the
decoders.pymodule. - Parsed messages are converted to change events and yieled from the
LogicalReplicationReader - Change events are nested Pydantic models where the tuple data (before/after) schema is dynamically generated depending on the table being processed.
First, setup a publication and a logical replication slot in the source database.
CREATE PUBLICATION test_pub FOR ALL TABLES;
SELECT * FROM pg_create_logical_replication_slot('test_slot', 'pgoutput');Second, run the script to collect the changes:
import os
import pypgoutput
HOST = os.environ.get("PGHOST")
PORT = os.environ.get("PGPORT")
DATABASE_NAME = os.environ.get("PGDATABASE")
USER = os.environ.get("PGUSER")
PASSWORD = os.environ.get("PGPASSWORD")
cdc_reader = pypgoutput.LogicalReplicationReader(
publication_name="test_pub",
slot_name="test_slot",
host=HOST,
database=DATABASE_NAME,
port=PORT,
user=USER,
password=PASSWORD,
)
for message in cdc_reader:
print(message.json(indent=2))
cdc_reader.stop()Generate some change messages
CREATE TABLE public.readme (id integer primary key, created_at timestamptz default now());
INSERT INTO public.readme (id) SELECT data FROM generate_series(1, 3) AS data;Output:
{
"op": "I",
"message_id": "4606b12b-ab41-41e6-9717-7ce92f8a9857",
"lsn": 23530912,
"transaction": {
"tx_id": 499,
"begin_lsn": 23531416,
"commit_ts": "2022-01-14T17:22:10.298334+00:00"
},
"table_schema": {
"column_definitions": [
{
"name": "id",
"part_of_pkey": true,
"type_id": 23,
"type_name": "integer",
"optional": false
},
{
"name": "created_at",
"part_of_pkey": false,
"type_id": 1184,
"type_name": "timestamp with time zone",
"optional": true
}
],
"db": "test_db",
"schema_name": "public",
"table": "readme",
"relation_id": 16403
},
"before": null,
"after": {
"id": 1,
"created_at": "2022-01-14T17:22:10.296740+00:00"
}
}
{
"op": "I",
"message_id": "1ede0643-42b6-4bb1-8a98-8e4ca10c7915",
"lsn": 23531144,
"transaction": {
"tx_id": 499,
"begin_lsn": 23531416,
"commit_ts": "2022-01-14T17:22:10.298334+00:00"
},
"table_schema": {
"column_definitions": [
{
"name": "id",
"part_of_pkey": true,
"type_id": 23,
"type_name": "integer",
"optional": false
},
{
"name": "created_at",
"part_of_pkey": false,
"type_id": 1184,
"type_name": "timestamp with time zone",
"optional": true
}
],
"db": "test_db",
"schema_name": "public",
"table": "readme",
"relation_id": 16403
},
"before": null,
"after": {
"id": 2,
"created_at": "2022-01-14T17:22:10.296740+00:00"
}
}
{
"op": "I",
"message_id": "fb477de5-8281-4102-96ee-649a838d38f2",
"lsn": 23531280,
"transaction": {
"tx_id": 499,
"begin_lsn": 23531416,
"commit_ts": "2022-01-14T17:22:10.298334+00:00"
},
"table_schema": {
"column_definitions": [
{
"name": "id",
"part_of_pkey": true,
"type_id": 23,
"type_name": "integer",
"optional": false
},
{
"name": "created_at",
"part_of_pkey": false,
"type_id": 1184,
"type_name": "timestamp with time zone",
"optional": true
}
],
"db": "test_db",
"schema_name": "public",
"table": "readme",
"relation_id": 16403
},
"before": null,
"after": {
"id": 3,
"created_at": "2022-01-14T17:22:10.296740+00:00"
}
}- Preference to use the built in pgoutput plugin. Some plugins are not available in managed database services such as RDS or cannot be updated to a new version.
- The pgoutput plugin includes useful metadata such as relid.
- logical decoding: https://www.postgresql.org/docs/12/logicaldecoding.html
- message specification: https://www.postgresql.org/docs/12/protocol-logicalrep-message-formats.html
- postgres publication: https://www.postgresql.org/docs/12/sql-createpublication.html
- psycopg2 replication support: https://www.psycopg.org/docs/extras.html#replication-support-objects
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