Db2 CDC

The Db2 CDC publisher captures row-level changes (inserts, updates, deletes) from a Db2 database using SQL Replication. Unlike MySQL and PostgreSQL which stream changes via replication protocols, Db2 CDC polls Change Data (CD) tables that are populated by the Db2 capture agent.

Note: Db2 CDC is currently marked as unstable and may undergo API changes in future releases.

Example

from typing import Tuple
import tabsdata as td

conn = td.Db2CdcConn(
    uri="db2://localhost:50000/ecommerce",
    credentials=td.UserPasswordCredentials(
        user=td.EnvironmentSecret("DB2_USER"),
        password=td.EnvironmentSecret("DB2_PASS"),
    ),
)

trigger = td.Db2CdcTrigger(
    conn=conn,
    tables=["ASN.TD_T__ORDERS", "ASN.TD_T__ORDER_ITEMS"],
    start_from="tail",
)

@td.publisher(
    trigger=trigger,
    tables=["orders", "order_items"],
)
def capture_ecommerce(
    orders: list[td.TableFrame],
    order_items: list[td.TableFrame],
) -> Tuple[td.TableFrame, td.TableFrame]:
    return td.concat(orders), td.concat(order_items)

This example publishes CDC data for the orders and order_items tables, capturing only changes that occur after the publisher has been first registered.

After defining the function, register it with a Tabsdata collection and trigger its execution.

Setup

Db2 must be configured to enable CDC before using this publisher. See Db2 Setup to Enable CDC.

Connection: Db2CdcConn

Db2CdcConn defines how to connect to the Db2 server. It accepts a standard Db2 URI and optional credentials.

conn = td.Db2CdcConn(
    uri="db2://localhost:50000/my_database",
    credentials=td.UserPasswordCredentials(
        user=td.EnvironmentSecret("DB2_CDC_USER"),
        password=td.EnvironmentSecret("DB2_CDC_PASSWORD"),
    ),
)

Parameter	Type	Description
uri	str	Db2 connection URI ( db2://host:port/database ). If the port is omitted, defaults to 50000 . If the database is omitted, defaults to "sample" .
credentials	UserPasswordCredentials	None
cx_src_configs_db2	dict	None

Trigger: Db2CdcTrigger

Db2CdcTrigger connects to Db2, polls the specified CD tables for new changes, and stages batches for downstream processing.

trigger = td.Db2CdcTrigger(
    conn=conn,
    tables=["ASN.TD_T__ORDERS", "ASN.TD_T__ORDER_ITEMS"],
    start_from="tail",
)

tables (CD Tables)

Unlike MySQL and PostgreSQL where you specify the source tables directly, the tables parameter in Db2 refers to the CD (Change Data) tables created during capture registration — not the original source tables.

A single source table can be registered for SQL Replication more than once, producing multiple CD tables with different configurations (e.g., different column subsets or capture schemas). By specifying the CD table, you select exactly which registration to consume from.

The connector automatically infers the original source table from the CD table by querying the ASN.ibmsnap_register metadata. Output TableFrames are named after the source tables, not the CD tables.

# Specify CD tables (created by capture registration), not source tables
tables=["ASN.TD_T__ORDERS", "ASN.TD_T__ORDER_ITEMS"]

# The connector resolves these to the original source tables
# (e.g., MY_SCHEMA.ORDERS, MY_SCHEMA.ORDER_ITEMS) automatically.

All CD tables must exist before the trigger starts.

Note: Schema changes on tracked tables are supported, but performing a schema change on a table for which CDC is enabled is a complex administration effort on the Db2 side. The Tabsdata publisher should be stopped while schema changes are being made. Refer to the IBM Db2 documentation for details on managing schema changes with SQL Replication.

start_from

Determines where the connector begins reading from the CD tables. Position is tracked via IBMSNAP_COMMITSEQ values. On subsequent runs, the connector resumes automatically from its last committed position.

Value	Type	Behavior
"head"	str	Start from the earliest available data in the CD tables.
"tail"	str	Start from the current end, capturing only new changes.
CommitSeqPosition(seq="...")	CommitSeqPosition	Resume from a specific commit sequence number (global across all tables).
TableCommitSeqPosition(seqs={...})	TableCommitSeqPosition	Resume from per-table commit sequence numbers.
TimestampPosition(ts=datetime(...))	TimestampPosition	Start from the first change at or after the given timestamp.

Advanced Configuration

CDC Output Format (cdc_format)

The cdc_format parameter controls how change data is structured in the output TableFrames, configured via CdcFormat.

from tabsdata.connector.cdc.common.typing import CdcFormat

cdc_format=CdcFormat(values_format="columns", flatten_values=True)

Parameter	Type	Default	Description
values_format	"columns"	"struct"	"map"
flatten_values	bool	True	When True , new values are promoted to individual top-level columns instead of being packed into a container column.

Metadata columns (always present)

Every output row includes the following metadata columns regardless of values_format:

Column	Type	Description
@td.cdc.meta.op	str	Operation type: "i" (insert), "u" (update), or "d" (delete).
@td.cdc.meta.tx	str	Transaction identifier from the source database.
@td.cdc.meta.sq	int	Sequence number ordering changes within a transaction.

values_format = "columns"

Each source table column is represented as two explicit output columns — one for the old value and one for the new value:

Column	Description
@td.cdc.data.col.old.<COL_NAME>	Value before the change.
@td.cdc.data.col.new.<COL_NAME>	Value after the change. Present when flatten_values=False .
<COL_NAME>	Value after the change. Present when flatten_values=True (replaces the new prefixed column).

Semantics by operation:

Operation	@td.cdc.data.col.old.<COL_NAME>	New value column
Insert ( i )	null	Inserted data
Update ( u )	Value prior to the update	Value after the update
Delete ( d )	null	Deleted data

values_format = "map"

Old and new values are packed into map columns keyed by table column name:

Column	Type	Description
@td.cdc.data.map.old	Map<str, str>	Old values. Present when flatten_values=False or for old values always.
@td.cdc.data.map.new	Map<str, str>	New values packed as a map. Present when flatten_values=False .
<COL_NAME>	—	New values as individual columns. Present when flatten_values=True (replaces @td.cdc.data.map.new ).

Semantics by operation:

Operation	@td.cdc.data.map.old	New value column(s)
Insert ( i )	null	Inserted data
Update ( u )	Values prior to the update	Values after the update
Delete ( d )	null	Deleted data

values_format = "struct"

Identical to "map" but old and new values are packed into struct fields instead of map columns:

Column	Type	Description
@td.cdc.data.row.old	struct	Old values. Present when flatten_values=False or for old values always.
@td.cdc.data.row.new	struct	New values packed as a struct. Present when flatten_values=False .
<COL_NAME>	—	New values as individual columns. Present when flatten_values=True (replaces @td.cdc.data.row.new ).

Semantics by operation are identical to "map" above.

Output Examples

values_format="columns", flatten_values=True

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	id	username	first_name	last_name	email	@td.cdc.data.col.old.id	@td.cdc.data.col.old.username	@td.cdc.data.col.old.first_name	@td.cdc.data.col.old.last_name	@td.cdc.data.col.old.email
i	225e1410-…:18	1	columns	true	1	deals_1914	Johnny	Woods	replaced1800@gmail.com	null	null	null	null	null
u	225e1410-…:19	1	columns	true	7	filename_2073	Gerardo	Mcintosh	surgery1995@duck.com	7	filename_2073	Maren	Puckett	examinations2009@yahoo.com
d	225e1410-…:20	1	columns	true	2	incl_1972	Emery	Reilly	exposed2025@example.com	null	null	null	null	null

values_format="columns", flatten_values=False

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	@td.cdc.data.col.new.id	@td.cdc.data.col.new.username	@td.cdc.data.col.new.first_name	@td.cdc.data.col.new.last_name	@td.cdc.data.col.new.email	@td.cdc.data.col.old.id	@td.cdc.data.col.old.username	@td.cdc.data.col.old.first_name	@td.cdc.data.col.old.last_name	@td.cdc.data.col.old.email
i	225e1410-…:22	1	columns	false	1	beat_1843	Kathyrn	Stokes	true1875@outlook.com	null	null	null	null	null
u	225e1410-…:23	1	columns	false	7	douglas_1901	Lawrence	Bauer	submission2025@yahoo.com	7	douglas_1901	Hermine	Preston	commodities1921@outlook.com
d	225e1410-…:24	1	columns	false	7	douglas_1901	Lawrence	Bauer	submission2025@yahoo.com	null	null	null	null	null

values_format="struct", flatten_values=True

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	id	username	first_name	last_name	email	@td.cdc.data.row.old
i	225e1410-…:26	1	struct	true	1	loops_1939	Agueda	Duncan	clinical2027@protonmail.com	{null,null,null,null,null}
u	225e1410-…:27	1	struct	true	8	evaluating_1979	Carletta	Deleon	wrapping1938@yandex.com	{8,”evaluating_1979”,”Marlen”,”Estrada”,”hitachi1882@example.org”}
d	225e1410-…:28	1	struct	true	4	majority_1865	Eulah	Whitney	touched1819@yahoo.com	{null,null,null,null,null}

values_format="struct", flatten_values=False

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	@td.cdc.data.row.new	@td.cdc.data.row.old
i	225e1410-…:30	1	struct	false	{1,”processes_2081”,”Leon”,”Pollard”,”browse1909@duck.com”}	{null,null,null,null,null}
u	225e1410-…:31	1	struct	false	{5,”virtually_1823”,”Gavin”,”Macdonald”,”rocky2058@yandex.com”}	{5,”virtually_1823”,”Erich”,”Hood”,”skin2004@gmail.com”}
d	225e1410-…:32	1	struct	false	{7,”thank_1865”,”Lashawna”,”Petty”,”classical2074@yandex.com”}	{null,null,null,null,null}

values_format="map", flatten_values=True

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	id	username	first_name	last_name	email	@td.cdc.data.map.old
i	225e1410-…:34	1	map	true	1	uni_2028	Sandy	Hinton	husband1960@example.org	{“id”:null,”username”:null,”first_name”:null,”last_name”:null,”email”:null}
u	225e1410-…:35	1	map	true	1	uni_2028	Kelle	Noel	see2021@example.com	{“id”:1,”username”:”uni_2028”,”first_name”:”Sandy”,”last_name”:”Hinton”,”email”:”husband1960@example.org”}
d	225e1410-…:36	1	map	true	1	uni_2028	Kelle	Noel	see2021@example.com	{“id”:null,”username”:null,”first_name”:null,”last_name”:null,”email”:null}

values_format="map", flatten_values=False

@td.cdc.meta.op	@td.cdc.meta.tx	@td.cdc.meta.sq	@td.cdc.meta.fmt	@td.cdc.meta.flat	@td.cdc.data.map.new	@td.cdc.data.map.old
i	a4a17b92-…:38	1	map	false	{“id”:1,”username”:”vacancies_2045”,”first_name”:”Tony”,”last_name”:”Oliver”,”email”:”rec1977@yandex.com”}	{“id”:null,”username”:null,”first_name”:null,”last_name”:null,”email”:null}
u	a4a17b92-…:39	1	map	false	{“id”:7,”username”:”strategies_1852”,”first_name”:”Foster”,”last_name”:”Nolan”,”email”:”ambient1829@example.com”}	{“id”:7,”username”:”strategies_1852”,”first_name”:”Doreatha”,”last_name”:”Mclaughlin”,”email”:”buffalo2065@yandex.com”}
d	a4a17b92-…:40	1	map	false	{“id”:8,”username”:”boc_1991”,”first_name”:”Peg”,”last_name”:”Vang”,”email”:”blacks1939@yandex.com”}	{“id”:null,”username”:null,”first_name”:null,”last_name”:null,”email”:null}

Start Position Examples

from tabsdata.connector.cdc.db2.typing import CommitSeqPosition, TableCommitSeqPosition
from tabsdata.connector.cdc.common.typing import TimestampPosition
from datetime import datetime, timezone

# Start from the end — capture only new changes going forward
start_from="tail"

# Start from the beginning of the CD tables
start_from="head"

# Resume from a global commit sequence number
start_from=CommitSeqPosition(seq="00000000000000001234")

# Resume with per-table commit sequence numbers
start_from=TableCommitSeqPosition(seqs={
    "my_schema.orders": "00000000000000001234",
    "my_schema.order_items": "00000000000000001200",
})

# Start from a specific timestamp
start_from=TimestampPosition(ts=datetime(2026, 1, 15, tzinfo=timezone.utc))

Buffer and Trigger Thresholds

The CDC connector uses a two-stage pipeline: changes accumulate in memory (buffer), are flushed to the working directory, then staged to the output location.

Buffer thresholds (memory → working directory)

Parameter	Type	Default	Description
buffer_max_rows	int	10,000	Flush to disk when row count in memory reaches this limit.
buffer_max_bytes	int	None	None
buffer_max_sec	float	60.0	Flush to disk when this many seconds have elapsed since the last flush.

Trigger thresholds (working directory → stage location)

Parameter	Type	Default	Description
trigger_max_rows	int	None	None
trigger_max_bytes	int	None	None
trigger_max_sec	float	60.0	Stage when this many seconds have elapsed since the last stage.

Other Parameters

Parameter	Type	Default	Description
poll_interval_sec	float	1.0	Seconds between polling the CD tables for new changes. Directly determines minimum capture latency.
blocking_timeout_sec	float	1.0	Timeout in seconds for blocking reads.
start	datetime	None	None
end	datetime	None	None

Limitations

• TRUNCATE: TRUNCATE TABLE operations are not captured. A truncate on a tracked table will not produce any change events.
• Large/Blob types: BLOB, CLOB, LONGBLOB, BYTEA, and TEXT (in some configurations) column types are not currently supported. Tables containing these types should exclude them from capture or use alternative ingestion methods.
• Static table list: All CD tables in the tables parameter must exist before the trigger starts. The connector does not perform runtime table discovery.

Db2 Setup to Enable CDC

The steps below are provided for convenience. Refer to the IBM Db2 documentation for comprehensive and up-to-date configuration instructions.

Enable Archive Logging

SQL Replication requires archive logging so the capture agent can read the recovery log.

mkdir $HOME/archive
mkdir $HOME/backup

db2 UPDATE DB CFG FOR my_database USING logarchmeth1 disk:$HOME/archive/

db2 BACKUP DB my_database TO $HOME/backup/

A full backup is required after enabling archive logging.

Create ASN Control Tables

The ASN control tables store capture metadata. Create them using the asnclp tool:

asnclp << EOF
SET SERVER CAPTURE TO DB my_database;
SET CAPTURE SCHEMA SOURCE ASN;
CREATE CONTROL TABLES FOR CAPTURE SERVER;
EOF

Start the Capture Agent

asncap capture_server=my_database capture_schema=ASN &

The capture agent runs continuously, reading the recovery log and writing changes to CD tables. It must be running before the connector can capture changes.

Register Tables for Capture

Each source table must be explicitly registered for CDC. Registration creates a corresponding CD table that stores captured changes.

asnclp << EOF
SET SERVER CAPTURE TO DB my_database;
SET CAPTURE SCHEMA SOURCE ASN;
SET RUN SCRIPT NOW STOP ON SQL ERROR ON;
CREATE REGISTRATION (
    my_schema.orders
)
DIFFERENTIAL REFRESH
IMAGE BOTH
PREFIX _
CAPTURE ALL;
EOF

Option	Description
DIFFERENTIAL REFRESH	Only changed rows are captured, not full table snapshots.
IMAGE BOTH	Both before-image and after-image are recorded for updates.
PREFIX _	Before-image column names are prefixed with underscore (e.g., _NAME for the old value of NAME ).
CAPTURE ALL	All column changes are captured.

After registration, insert a CAPSTART signal to activate capture and wait for the capture agent to process it:

INSERT INTO ASN.ibmsnap_signal
    (signal_type, signal_subtype, signal_input_in, signal_state)
VALUES
    ('CMD', 'CAPSTART', 'ASN.MY_SCHEMA_ORDERS', 'P');

-- Verify capture is active (signal_state should become 'C')
SELECT signal_state FROM ASN.ibmsnap_signal
WHERE signal_input_in = 'ASN.MY_SCHEMA_ORDERS';

Create a CDC User

Create a dedicated Db2 user with the privileges required to read the CD tables and ASN metadata:

GRANT SELECT ON TABLE ASN.ibmsnap_register TO USER cdc_user;
GRANT SELECT ON TABLE ASN.TD_T__ORDERS TO USER cdc_user;
GRANT SELECT ON TABLE ASN.TD_T__ORDER_ITEMS TO USER cdc_user;