ematix-flow 0.2.0

Move data between databases, files, and streams from Python. 5.87× faster than PySpark. No JVM needed.

ematix-flow

A declarative Python framework for moving and transforming data between databases, files, and streaming sources. Rust + Apache Arrow under the hood.

Status: v0.1.2 on PyPI as ematix-flow. All four surfaces below — declarative pipelines, multi-backend, streaming, stream processing — are shipped and stable.

ematix-flow lets you declare a target table and a load strategy in Python; the framework handles schema evolution, watermarks, restart-safe state, at-least-once delivery, and change-data- capture. Pipelines carry their own schedule="*/5 * * * *" and fire from flow run-due (drop that into cron / a k8s CronJob / GitHub Actions and you have a working pipeline tier with no scheduler service to operate). Plug in Airflow / Dagster / Prefect if you'd rather, by calling each pipeline's .sync() directly. The same primitives power batch loads (Postgres, MySQL, SQLite, DuckDB), file targets (Parquet, CSV, JSON, ORC, Delta Lake — local or S3), and long-running streaming consumers (Kafka, RabbitMQ, GCP Pub/Sub, AWS Kinesis).

The rest of this README walks through how to use it, in the order you'd reach for each feature.

---

Table of contents

1. Install
2. Connections
3. Backends
4. Pipelines
5. Modes
6. Scheduling
7. Streaming pipelines
8. Stream processing
9. Configuration reference
10. CLI
11. Python API
12. Performance and comparisons
13. What's shipped
14. Development
15. License

---

Install

pip install ematix-flow

The core install ships every backend, the flow CLI binary, and the run_pipeline / run_streaming_pipeline Python entrypoints.

Optional extras

Extra	What it adds	Install
df	DataFrame interop helpers (polars / pandas) for to_polars() / to_pandas() materialization.	pip install "ematix-flow[df]" then pip install polars (or pandas).
spark	PySpark interop helpers (to_pyspark() / from_pyspark()). Pulls in PySpark + JVM JDBC. Heavy.	pip install "ematix-flow[spark]"
pyarrow	Required for the streaming-backend pyclass wrappers (KafkaBackend, KinesisBackend, …) when you want batch-by-batch iteration in Python.	pip install pyarrow

The flow binary, run_pipeline, and the typed-Python streaming API work without any extras. To build from source, see Development at the bottom.

---

Connections

Connections are the first thing to set up. Every pipeline references one or more connections by name; ematix-flow resolves that name through a layered chain so you can keep secrets out of code.

Resolution chain

A connection name like "warehouse" resolves through these sources, highest priority first:

1. Env var EMATIX_FLOW_DSN_<NAME> — uppercase the name (EMATIX_FLOW_DSN_WAREHOUSE=postgres://...).
2. Env var EMATIX_FLOW_DSN — only matches the literal name default. Convenient for one-off scripts.
3. ./.ematix-flow.toml in the current directory.
4. ~/.ematix-flow/connections.toml for user-wide defaults.
5. In-process registration — register_connection(...), @ematix.connection, or inline config.connect(url=...).

flow connections list             # what's resolved + from where
flow connections check warehouse  # connect + report

Declaring connections

Three interchangeable forms — pick whichever fits the workflow.

TOML file

# ~/.ematix-flow/connections.toml
[connections.warehouse]
url = "postgres://user:${WAREHOUSE_PASSWORD}@host/wh"

[connections.kafka_prod]
kind = "kafka"
bootstrap_servers = "${KAFKA_BOOTSTRAP}"
group_id = "ematix-flow"

${VAR} interpolation lets secrets stay out of the file.

@ematix.connection decorator

from ematix_flow import ematix

@ematix.connection
class warehouse:
    kind = "postgres"
    url = "${WAREHOUSE_DSN}"          # ${VAR} interpolates at use time

@ematix.connection
class kafka_prod:
    kind = "kafka"
    bootstrap_servers = "${KAFKA_BOOTSTRAP}"
    group_id = "ematix-flow"
    sasl_plain_username = "${KAFKA_USER}"
    sasl_plain_password = "${KAFKA_PASS}"

After import, warehouse and kafka_prod are typed Connection instances registered in the runtime. Pass them by reference, or look them up by name string.

Typed instance + register_connection

from ematix_flow import PostgresConnection, register_connection

warehouse = register_connection(
    PostgresConnection(name="warehouse", url="postgres://localhost/wh"),
)

Useful when the connection has to be built dynamically (e.g. from an environment-driven dict).

Credential redaction

Every typed connection redacts secrets in repr() by field-name match (password, secret, secret_access_key, anything matching _password, AMQP URL passwords, etc.). Printing a connection in a notebook will not spill credentials.

Schema Registry as a connection

Avro / Protobuf pipelines reference a Schema Registry the same way:

@ematix.connection
class sr_prod:
    kind = "schema_registry"
    url = "${SR_URL}"

@ematix.connection
class kafka_avro:
    kind = "kafka"
    bootstrap_servers = "${KAFKA_BOOTSTRAP}"
    payload_format = "avro"
    schema_registry = "sr_prod"      # name reference

---

Backends

Every source and target lives behind one Backend trait. Switch a pipeline's target by changing one line.

Backend	Batch source	Streaming source	Target	DDL planning	Strategy executors (append / merge / scd2 / truncate)	CDC target
Postgres	✅	—	✅	✅	✅ (native + COPY BINARY)	✅
MySQL	✅	—	✅	✅	✅ (ON DUPLICATE KEY)	✅
SQLite	✅	—	✅	✅	✅	✅
DuckDB	✅	—	✅	✅	✅	✅
Delta Lake (local + S3)	✅	✅	✅	n/a	✅ (DataFusion-backed MERGE)	✅
Object stores (Parquet / CSV / ORC / JSONL, local + S3)	✅	✅	✅	n/a	append + truncate	— (see Δ.X3)
Kafka	—	✅	✅	n/a	append (cross-backend)	source role only
RabbitMQ	—	✅	✅	n/a	append (cross-backend)	—
GCP Pub/Sub	—	✅	✅	n/a	append (cross-backend)	—
AWS Kinesis	—	✅	✅	n/a	append (cross-backend)	—

Batch source = readable by @ematix.pipeline (the function returns a SQL string; the framework executes it against the source connection). Streaming source = tailable by flow consume / @ematix.streaming_pipeline (long-running consumer with manual offset commit / ack). Target = writable by either pipeline shape. Cross-backend moves stream Apache Arrow batches end-to-end — same-DB pairs take the INSERT … SELECT fast path automatically.

Streaming source guarantees

• Manual offset commit / ack. Pipelines call commit_offsets() on the source only after a durable target write — at-least-once end-to-end. Kafka offsets, RabbitMQ basic_ack, Pub/Sub handler acks, and Kinesis per-shard sequence numbers all flow through the same surface.
• Exactly-once. Kafka producer-side via transactions; consumer-coordinated end-to-end via KafkaToKafkaEosPipeline.
• DLQ. Both app-level (dead_letter_topic routes failed batch rows to a separate target) and broker-level (RabbitMQ x-dead-letter-exchange, Pub/Sub subscription dead_letter_policy).
• Schema Registry. Avro and Protobuf decode/encode via Confluent SR or Apicurio.

Cross-backend reads + writes

When source and target are on the same database, ematix-flow uses an INSERT … SELECT fast path. When they differ, the framework streams Apache Arrow batches between them — no row-by-row serialization, no intermediate file roundtrip. Switching from Postgres → Postgres to Postgres → Delta Lake is a one-line change.

---

Pipelines

A pipeline binds a source query to a target table and a load strategy. The minimum surface:

from typing import Annotated
from ematix_flow import ematix, pk
from ematix_flow.types import BigInt, Text, TimestampTZ

@ematix.connection
class warehouse:
    kind = "postgres"
    url = "${WAREHOUSE_DSN}"

@ematix.table(schema="analytics")
class Events:
    event_id: Annotated[BigInt, pk()]
    name: Text | None
    received_at: TimestampTZ

@ematix.pipeline(
    target=Events,
    target_connection="warehouse",
    schedule="*/5 * * * *",
    mode="append",
)
def ingest_events(conn):
    return "SELECT event_id, name, received_at FROM raw.events"

That's the full file. Run it:

flow run --module my_pipelines ingest_events     # one-shot
flow run-due --module my_pipelines               # cron-style
flow preview --module my_pipelines ingest_events # what would it do?
flow validate --module my_pipelines ingest_events # EXPLAIN against the DB

Tables

@ematix.table declares the target schema. Columns are typed with PEP-593 annotations + markers:

from ematix_flow.normalize import lower, trim, empty_to_null, parse_timestamp
from ematix_flow.types import String

@ematix.table(schema="analytics")
class CustomerDim:
    customer_id: Annotated[BigInt, pk()]                          # primary key
    email: Annotated[String[256] | None, lower(), trim(), empty_to_null()]
    name: Text | None
    updated_at: Annotated[TimestampTZ, parse_timestamp()]

The class name maps to the table name (CustomerDim → customer_dim); override with @ematix.table(schema=..., name="..."). pk() and natural_key() markers control merge keys (see Modes below). Normalization markers (lower, trim, empty_to_null, parse_timestamp, parse_int, regex_replace, default, derive, raw sql) compile to in-database SQL — no Python row loop.

Source / target wiring

@ematix.pipeline(
    target=CustomerDim,
    source_connection="raw_db",       # if omitted, defaults to target_connection
    target_connection="warehouse",    # required (or set via EMATIX_FLOW_DSN_<NAME>)
    schedule="0 * * * *",
    mode="scd2",
    compare_columns=["email", "name"],
)
def sync_customers(conn):
    # `conn` is the source connection.
    return "SELECT customer_id, email, name, updated_at FROM customers"

Element	Where it's configured
Target table	schema= on @ematix.table + the class name (snake-cased).
Source query	The SQL string returned from the decorated function. Can be a join, subquery, parametrised WHERE, etc.
Connections	source_connection= and target_connection= reference names from the Connections registry.
Source/target separation	Set both to cross databases. ematix-flow auto-switches between same-DB INSERT … SELECT and cross-DB Arrow streaming.

Two function signatures

def sync(conn):  return "SELECT …"   # dynamic SQL: filters, dates, etc.
def sync():      pass                # static — pair with source_table=

The static form skips boilerplate when the source is a single table:

@ematix.pipeline(
    target=CustomerDim,
    target_connection="warehouse",
    source_table="raw.customers",      # framework synthesizes SELECT
    column_map={"target_col": "source_col"},  # optional rename map
    mode="merge",
    schedule="0 * * * *",
)
def sync_customers():
    pass

Multi-target fan-out

One source query, N targets:

from ematix_flow import Target

@ematix.pipeline(
    targets=[
        Target(table=CustomerDim,    connection="warehouse"),
        Target(table=CustomerArchive, connection="lake"),
    ],
    source_connection="raw_db",
    schedule="0 * * * *",
    mode="merge",
)
def sync_customers(conn):
    return "SELECT customer_id, email, name, updated_at FROM customers"

Each target gets its own strategy executor; failures on one target don't block the others (configurable via continue_on_target_failure=True).

---

Modes

The load strategy. Set on @ematix.pipeline(mode=...).

append

Insert all source rows. No deduplication, no updates.

@ematix.pipeline(target=Events, mode="append", schedule="*/5 * * * *")
def ingest(conn):
    return "SELECT event_id, name, received_at FROM raw.events"

Use with incremental=True and a watermark_column= to filter to new rows on each run; ematix-flow tracks the last-loaded watermark in ematix_flow.watermarks.

truncate

TRUNCATE (or DELETE FROM) the target, then load. Useful for small reference / dimension tables that get reloaded fully each run.

merge (a.k.a. scd1)

Insert new rows; update existing rows on PK match. Same as upserting on conflict. Compare columns control which non-key fields participate in the update:

@ematix.pipeline(
    target=CustomerDim,
    mode="merge",
    compare_columns=["email", "name"],   # only update if these change
    schedule="0 * * * *",
)
def sync(conn):
    return "SELECT customer_id, email, name FROM raw.customers"

scd2

Slowly-changing dimension type 2. Closes the previous version of each row and inserts a new one when the compare columns change. ematix-flow auto-augments the table with valid_from, valid_to, is_current, row_hash:

@ematix.pipeline(
    target=CustomerDim,
    mode="scd2",
    compare_columns=["email", "name"],
    event_timestamp_column="updated_at",  # use updated_at as valid_from
    ttl_seconds=86_400 * 30,              # auto-close versions older than 30d
    schedule="0 * * * *",
)
def sync(conn):
    return "SELECT customer_id, email, name, updated_at FROM raw.customers"

How merge keys are resolved

For merge and scd2, keys= is optional. Resolution priority:

1. Explicit keys=("col_a", "col_b") on @ematix.pipeline.
2. __merge_keys__ = ("col_a", "col_b") class dunder on the table.
3. First natural_key() group on the table — for SCD2 where the business key differs from the versioned PK.
4. Columns marked pk().

A UserWarning fires when steps 2 or 3 resolve to keys that differ from pk(). Pass keys= explicitly to silence.

Incremental loads + watermarks

@ematix.pipeline(
    target=Events,
    mode="append",
    incremental=True,
    watermark_column="received_at",    # filter source rows > last watermark
    schedule="*/5 * * * *",
)
def ingest(conn):
    return "SELECT event_id, name, received_at FROM raw.events"

Watermarks live in ematix_flow.watermarks and advance only after a successful target commit — restart-safe.

Pre- and post-load transforms

from ematix_flow.transforms import deduplicate_by, filter_where

@ematix.pipeline(
    target=Events,
    mode="merge",
    transforms_pre=[
        deduplicate_by(keys=("event_id",), order_by="received_at desc"),
        filter_where("name IS NOT NULL"),
    ],
    transforms_post=[
        "ANALYZE analytics.events",         # raw SQL string
        ematix.transform_ref("update_mart"), # named transform
    ],
    continue_on_failure_post=True,
    schedule="*/5 * * * *",
)
def ingest(conn): ...

transforms_pre compile to in-database SQL ahead of the load. transforms_post each run in their own transaction.

---

Scheduling

Three ways to fire a pipeline.

Cron (schedule= on the decorator)

@ematix.pipeline(target=Events, mode="append", schedule="*/5 * * * *")
def ingest(conn): ...

Then run on any cadence (cron / k8s CronJob / GitHub Actions):

flow run-due --module my_pipelines

run-due fires every pipeline whose schedule expires within the last interval. Idempotent — running it twice in the same window re-fires nothing because watermarks advance only after success.

One-shot

flow run     --module my_pipelines ingest        # run now
flow preview --module my_pipelines ingest        # what would it do? (dry-run, no commit)
flow validate --module my_pipelines ingest       # EXPLAIN against the DB

Programmatic

from my_pipelines import ingest
ingest.sync(keys=("event_id",))     # pipelines expose a `.sync()` method

Useful for tests, notebooks, or wrapping a pipeline inside another orchestrator.

Run history

Every run lands in ematix_flow.run_history with a run_id, status, row counts, error message (if any), and metrics JSON. Inspect via SQL or flow runs list.

---

Streaming pipelines

A long-running consumer that drains a source and writes batches to a target with manual at-least-once offset commits, Prometheus metrics, and exponential-backoff supervised restart.

TOML form

# pipeline.toml
pipeline_name = "events-to-pg"
source_query  = "events"
idle_pause_ms = 500

[source]
kind = "kafka"
bootstrap_servers = "localhost:9092"
group_id = "ematix-flow"

[target]
kind = "postgres"
url  = "postgres://localhost/mydb"

[target.table]
schema = "public"
name   = "events"

Run from Python:

from ematix_flow import run_pipeline
run_pipeline(config="pipeline.toml", metrics_port=9100)

Or from the CLI binary:

flow consume pipeline.toml \
    --metrics-port 9100 \
    --restart-on-error \
    --max-backoff-ms 30000

Typed-Python form (decorator, no TOML)

# my_pipelines.py
from ematix_flow import ematix

@ematix.connection
class kafka_prod:
    kind = "kafka"
    bootstrap_servers = "${KAFKA_BOOTSTRAP}"
    group_id = "ematix-flow"

@ematix.connection
class warehouse:
    kind = "postgres"
    url = "${WAREHOUSE_DSN}"

@ematix.streaming_pipeline(
    name="events_to_pg",
    source=kafka_prod,
    source_query="events",
    target=warehouse,
    target_table=("public", "events"),
)
def events_to_pg():
    pass

flow consume      --module my_pipelines events_to_pg --metrics-port 9100
flow consume-list --module my_pipelines              # show registered pipelines

The framework renders the equivalent TOML internally and hands it to the same Rust runtime — same at-least-once guarantees, same metrics, same supervisor.

Multi-target fan-out

from ematix_flow import Target, ObjectStoreS3Connection

@ematix.connection
class lake:
    kind = "object_store_s3"
    endpoint = "https://s3.amazonaws.com"
    bucket = "ematix-archive"
    region = "us-east-1"
    access_key_id = "${AWS_ACCESS_KEY_ID}"
    secret_access_key = "${AWS_SECRET_ACCESS_KEY}"
    format = "parquet"

@ematix.streaming_pipeline(
    name="events_fanout",
    source=kafka_prod,
    source_query="events",
    targets=[
        Target(connection=warehouse, table=("public", "events")),
        Target(connection=lake, prefix="events/raw", parquet_compression="zstd"),
    ],
)
def events_fanout(): pass

Each target gets its own write path; failures on one don't stop the others (configurable).

---

Stream processing

Stateful transforms layered onto a streaming pipeline.

SQL transforms

Mid-stream SELECT via DataFusion — filter / project / cast / lookup-join. Static lookups load from any backend at startup; refresh_interval_ms per lookup runs a background refresh task.

run_streaming_pipeline(
    name="events-clean",
    source=kafka_prod, source_query="events",
    target=warehouse,  target_table=("public", "events_clean"),
    transform_sql="""
      SELECT s.user_id, s._event_ts, u.tier
      FROM source s
      LEFT JOIN users u ON u.user_id = s.user_id
    """,
    lookups={"users": Lookup(connection=warehouse,
                             query="SELECT user_id, tier FROM dim_users",
                             refresh_interval_ms=60_000)},
)

Aggregating many source rows into one JSON-shaped target row

When the target schema isn't 1:1 with the source — e.g. an option_chain_snapshots(minute, strikes_json) table where every row carries a JSON array of N contracts for that minute — DataFusion's array_agg(named_struct(...)) does the pivot inside a single transform_sql pass. The framework's Postgres write path serializes Arrow List<Struct<...>> straight into a JSONB column, so no staging table or two-stage pipeline is needed.

run_streaming_pipeline(
    name="option-chain-snapshots",
    source=s3,                                # CSV files under a watched prefix
    source_query="raw/options/",
    target=warehouse,                         # postgres
    target_table=("marketdata", "option_chain_snapshots"),
    transform_sql="""
      SELECT
        date_trunc('minute', ts) AS minute,
        array_agg(named_struct(
          'strike', strike,
          'bid',    bid,
          'ask',    ask
        )) AS strikes_json
      FROM source
      WHERE underlying = 'SPXW' AND days_to_expiry = 0
      GROUP BY 1
    """,
)

The mirror table:

CREATE TABLE marketdata.option_chain_snapshots (
  minute        TIMESTAMPTZ NOT NULL,
  strikes_json  JSONB NOT NULL  -- [{"strike": 4500, "bid": 1.25, "ask": 1.30}, ...]
);

Same shape works for MERGE / SCD2 / Truncate strategies via the strategy executor — the JSONB column round-trips like any other type.

For functions DataFusion's stdlib doesn't cover (cumulative-normal CDF, custom hashing, day-count conventions), register a Python scalar UDF — covered in the next section.

Python UDFs (@ematix_flow.udf)

Wrap a Python callable as a DataFusion scalar UDF and call it from transform_sql. Per-batch dispatch through PyArrow zero-copy: one GIL acquisition + PyArrow round-trip per batch (typically thousands of rows), so vectorised numpy / pyarrow.compute inside the callable amortises the overhead.

import math

import numpy as np
import pyarrow as pa

from ematix_flow import run_streaming_pipeline, udf


@udf(args=("Float64", "Float64", "Float64", "Float64", "Float64"),
     returns="Float64")
def bs_call_delta(strike, spot, vol, rate, expiry):
    # All five inputs arrive as PyArrow Float64 Arrays; convert
    # once, do the math vectorised, ship a PyArrow Array back.
    k = strike.to_numpy(zero_copy_only=False)
    s = spot.to_numpy(zero_copy_only=False)
    v = vol.to_numpy(zero_copy_only=False)
    r = rate.to_numpy(zero_copy_only=False)
    t = expiry.to_numpy(zero_copy_only=False)
    d1 = (np.log(s / k) + (r + 0.5 * v * v) * t) / (v * np.sqrt(t))
    cdf = 0.5 * (1.0 + np.vectorize(math.erf)(d1 / np.sqrt(2)))
    return pa.array(cdf, type=pa.float64())


run_streaming_pipeline(
    name="option-chain-with-greeks",
    source=s3, source_query="raw/options/",
    target=warehouse, target_table=("marketdata", "option_chain_snapshots"),
    transform_sql="""
        SELECT
          date_trunc('minute', ts) AS minute,
          array_agg(named_struct(
            'strike', strike,
            'bid',    bid,
            'ask',    ask,
            'delta',  bs_call_delta(strike, spot, vol, rate, expiry)
          )) AS strikes_json
        FROM source
        GROUP BY 1
    """,
    udfs=[bs_call_delta],
)

Argument and return types are DataFusion DataType strings — "Int64", "Float64", "Utf8", "Boolean", etc. Mismatched call sites surface at plan-compile time as DataFusion type errors. Two UDFs registering under the same name is a config-load error — no silent shadowing.

Python aggregate UDFs (@ematix_flow.udaf)

For per-group reductions DataFusion's stdlib doesn't ship (VWAP, custom percentiles, distinct-by-cardinality), decorate a Python class with @udaf and pass it as aggregate_udfs=. The class must expose four methods — update_batch, merge_batch, evaluate, state — mirroring DataFusion's Accumulator trait. PyArrow zero-copy on the inputs, length-1 PyArrow Arrays on the outputs.

import pyarrow as pa
import pyarrow.compute as pc

from ematix_flow import run_streaming_pipeline, udaf


@udaf(args=("Float64", "Float64"),
      state=("Float64", "Float64"),
      returns="Float64", name="vwap")
class Vwap:
    def __init__(self):
        self.num = 0.0
        self.den = 0.0

    def update_batch(self, prices, qtys):
        self.num += pc.sum(pc.multiply(prices, qtys)).as_py() or 0.0
        self.den += pc.sum(qtys).as_py() or 0.0

    def merge_batch(self, num_states, den_states):
        self.num += pc.sum(num_states).as_py() or 0.0
        self.den += pc.sum(den_states).as_py() or 0.0

    def evaluate(self):
        if self.den == 0:
            return pa.array([None], type=pa.float64())
        return pa.array([self.num / self.den], type=pa.float64())

    def state(self):
        return (pa.array([self.num], type=pa.float64()),
                pa.array([self.den], type=pa.float64()))


run_streaming_pipeline(
    name="vwap-per-minute",
    source=kafka_quotes, source_query="quotes",
    target=warehouse, target_table=("marketdata", "vwap_per_minute"),
    transform_sql="""
      SELECT date_trunc('minute', ts) AS minute,
             vwap(price, qty)          AS vwap
      FROM source GROUP BY 1
    """,
    aggregate_udfs=[Vwap],
)

Per-batch dispatch (one GIL acquisition + PyArrow round-trip per batch, accumulator instance survives across batches within a group), vectorise with pyarrow.compute or numpy inside the methods. See the user guide for the full state-shape contract + the pure-Rust escape hatch when GIL contention dominates.

Tumbling / hopping windows

Nine aggregators including HLL+ approximate count_distinct. late_data = "drop" | "reopen" | "dlq", idle-tick emission, per-window max_groups_per_window fail-loud cap.

from ematix_flow import Window, Aggregation

run_streaming_pipeline(
    name="events-per-min",
    source=kafka_prod, source_query="events",
    target=warehouse,  target_table=("public", "events_per_min"),
    transform_sql="SELECT user_id, _event_ts FROM source",
    window=Window(
        kind="tumbling",
        duration_ms=60_000,
        group_by=("user_id",),
        max_groups_per_window=1_000_000,
        aggregations=[Aggregation(agg="count", as_="n")],
    ),
)

Session windows

Gap-based per-key sessions with mandatory max_session_duration_ms hard cap. Out-of-order session merging under Reopen. Mandatory StateStore for restart safety.

from ematix_flow import StateStore

run_streaming_pipeline(
    name="user-sessions",
    source=kafka_prod, source_query="events",
    target=warehouse,  target_table=("public", "user_sessions"),
    transform_sql="SELECT user_id, page, _event_ts FROM source",
    window=Window(
        kind="session",
        gap_ms=300_000,                       # 5-min idle = session boundary
        max_session_duration_ms=86_400_000,   # 24h hard cap
        group_by=("user_id",),
        max_groups_per_window=1_000_000,
        aggregations=[
            Aggregation(agg="count", as_="events"),
            Aggregation(agg="first", column="page", as_="entry_page"),
            Aggregation(agg="last",  column="page", as_="exit_page"),
        ],
    ),
    state_store=StateStore(kind="postgres", url="postgres://localhost/ematix_state"),
)

Stream-stream joins

Keyed time-windowed inner / outer joins. Per-side per-key buffers, watermark-driven retention, retained-buffer reopen for late matches.

from ematix_flow import Join, Source

run_streaming_pipeline(
    name="orders-payments",
    sources=[
        Source(connection=kafka_prod, query="orders"),
        Source(connection=kafka_prod, query="payments"),
    ],
    target=warehouse,
    target_table=("public", "orders_with_payments"),
    join=Join(
        left_source="orders",
        right_source="payments",
        left_keys=("order_id",),
        right_keys=("order_id",),
        time_window_ms=300_000,                # ±5 min symmetric
        # kind="left_outer",                   # or "right_outer" / "full_outer"
        # min_delta_ms=-60_000, max_delta_ms=300_000,  # asymmetric
        # late_data="reopen", allowed_lateness_ms=10_000,
    ),
    state_store=StateStore(kind="postgres", url="postgres://localhost/ematix_state"),
)

Change-data-capture

Apply Debezium / Maxwell / custom CDC envelopes to a target table with proper per-op semantics (insert on c, update on u, delete or soft-delete on d):

from ematix_flow import CDC

@ematix.streaming_pipeline(
    name="mirror_customers",
    source=kafka_prod,
    source_query="dbserver1.public.customers",
    target=customer_mirror,
    target_connection=warehouse,
    cdc=CDC(envelope="debezium"),
)
def mirror_customers(): pass

Per-PK idempotency gate (ematix_flow.cdc_idempotency) keeps Kafka redeliveries from double-applying. Schema-evolution policy (Skip / Fail) controls drift behaviour. Hard or soft delete (delete_mode="soft", soft_delete_column="deleted_at"). Supported targets: Postgres, Delta Lake (local + S3), DuckDB, SQLite, MySQL.

Raw object stores (S3 / GCS / Azure Parquet, CSV, JSON) are intentionally not CDC targets — those file formats are immutable, so per-event UPDATE / DELETE has no clean shape. For CDC into object storage, use DeltaS3Backend: Delta sits on top of the same object stores and gives you transactional MERGE for free. The append-only "event log" pattern (one row per change event, materialise current state downstream) remains buildable ad-hoc with the existing transform stage + ObjectStore target.

End-to-end demos:

• examples/cdc-debezium/ — Postgres source → Debezium → Kafka → Postgres mirror.
• examples/cdc-delta/ — same shape but the target is a local Delta Lake table.

Distributed batch SQL (opt-in)

Set engine = "distributed" + peers = [...] and the SQL fans out across a peer-to-peer mesh of flow-worker processes via Apache Arrow Flight. mTLS for the mesh, cross-pod lookup broadcast, no separate cluster service. SQL dialect translator (Spark / DuckDB → DataFusion) makes existing queries portable without rewrites.

---

Configuration reference

Selected knobs that don't fit any single section above. Every knob is reachable from typed Python; most also have a TOML equivalent.

Watermark behaviour

from ematix_flow import Watermark

run_streaming_pipeline(
    ...,
    watermark=Watermark(
        lateness_ms=5_000,           # how late an event can arrive
        source_idleness_ms=120_000,  # advance watermark when source is idle
    ),
)

Per-batch error policy

run_streaming_pipeline(
    ...,
    transform_on_error="dlq",         # "fail" (default) | "drop" | "dlq"
    dead_letter_topic="events-failed",
)

Object-store write options

Target(
    connection=lake,
    prefix="events/raw",
    parquet_compression="zstd",       # or "snappy" / "gzip" / "uncompressed"
)

Target(
    connection=lake,
    prefix="events/csv",
    csv_delimiter=";",
    csv_header=False,
)

The typed-Python boundary catches mis-shaped combos (e.g. setting parquet_compression on a CSV target) before TOML round-trip.

State store

Every stateful transform (sessions, joins) requires a StateStore:

StateStore(
    kind="postgres",
    url="postgres://localhost/ematix_state",
    checkpoint_interval_ms=60_000,    # periodic dirty-state flush cadence
)

In-memory mode is for tests only. Pipeline config-load emits a loud warning if kind="in_memory" is paired with a stateful transform.

Schema Registry + payload format

@ematix.connection
class kafka_avro:
    kind = "kafka"
    bootstrap_servers = "${KAFKA_BOOTSTRAP}"
    payload_format = "avro"           # or "protobuf" / "json"
    schema_registry = "sr_prod"       # name reference

Connection introspection

flow connections list
flow connections check warehouse
flow connections set warehouse url=postgres://...

---

CLI

flow list                # registered pipelines
flow run <name>          # one-shot
flow run-due             # cron-style fire of all due pipelines
flow preview <name>      # dry-run, no commit
flow validate <name>     # EXPLAIN against the target
flow runs list           # recent runs from ematix_flow.run_history
flow connections list / check / set
flow transform list / run

flow consume <toml>      # streaming daemon (TOML form)
flow consume --module my_pipelines <name>   # typed-Python form
flow consume-list --module my_pipelines     # registered streaming pipelines

--module points at any importable Python module. --metrics-port exposes Prometheus metrics. --restart-on-error --max-backoff-ms enables the supervised-restart loop.

---

Python API

For when you want to bypass the pipeline orchestration and use a streaming backend directly — e.g. in a notebook for ad-hoc exploration:

from ematix_flow._core import KafkaBackend

backend = KafkaBackend.open(
    "localhost:9092",
    group_id="ematix-flow",
    payload_format="avro",
    schema_registry_url="http://localhost:8081",
    sasl_plain_username="alice",
    sasl_plain_password="secret",
)
backend.ping()

for batch in backend.iter_arrow_stream("events"):
    process(batch)               # batch is pyarrow.RecordBatch

backend.commit_offsets()         # at-least-once: ack only after success

The same shape works for RabbitMQBackend, PubSubBackend, and KinesisBackend (each in ematix_flow._core).

For polars / pandas / pyspark interop after a pipeline run, see the Install extras and the docs/USER_GUIDE.md walkthrough.

---

Performance and comparisons

ematix-flow uses DataFusion for in-process SQL and Apache Arrow for cross-backend I/O. Single-node TPC-H benchmarks (M3 Pro):

Suite	Geomean speedup vs PySpark local[*]	Range
TPC-H SF=1 (22 queries)	5.87×	1.78× to 16.74×
TPC-H SF=10 (representative subset)	3.3×	—

22/22 PASS on TPC-H SF=1; 103/103 PASS on the canonical Apache Spark TPC-DS plan-time audit (Spark dialect → DataFusion via the built-in translator).

Distributed batch SQL across multiple ematix-flow processes is available via the bundled flow-worker peer mesh. Cross-host scaling claims are honestly framed as deferred — there's no cluster hardware in this project's runway.

Full methodology, hardware, and per-query numbers: docs/BENCHMARKS.md.

How it compares

If you're running…	…ematix-flow replaces…
One-off pandas / SQL scripts	Adds correctness guarantees (watermarks, atomic state, schema evolution) without the operational weight of Airflow + Spark.
Airflow + dbt	Handles the load logic and streaming sources without a scheduler tier. Cron / k8s CronJob / GitHub Actions all fire flow run-due — no Airflow worker, no scheduler stub, no DAG plumbing.
Kafka Connect + Debezium + custom sinks	First-class CDC source mode dispatches per-op transactionally to your existing target. No JVM connectors to operate.
PySpark Structured Streaming (single-node)	Same SQL surface (DataFusion + Spark dialect translator), 5.87× faster geomean, no cluster manager, no JVM.

---

What's shipped

All four surfaces are stable. See docs/ROADMAP.md for the consolidated "what's left" punch list (release polish, deferred-feature extensions, open design questions).

Test surface (workspace-wide, every PR)

• 459 Rust core unit tests
• 124 Rust CLI unit tests + 27 backend-config scaffold round-trip tests across all 10 backends + distributed + TLS config
• ~80 Rust testcontainers integration tests (Docker-gated)
• 376 default Python tests + ~196 testcontainers-gated Python tests
• 22-query TPC-H audit: 22/22 PASS at SF=1
• 103-query TPC-DS Spark-dialect audit: 103/103 PASS plan-time

clippy + fmt clean on stable Rust; cargo audit green against RustSec; ruff + bandit + pip-audit green on the Python side.

Phase plans (for the curious)

• docs/PRD.md — original v0.1 product spec
• docs/IMPLEMENTATION_PLAN.md — Phases 0–14
• docs/MULTI_BACKEND_PLAN.md — Phases 30–38 (multi-DB + streaming + CLI)
• docs/ERGONOMICS_PLAN.md — decorator API design
• docs/SQL_TRANSFORMS_PLAN.md — Phase 39 stream-processing umbrella
• docs/PHASE_39_4_WINDOWS.md — tumbling + hopping windows
• docs/PHASE_39_5_SESSIONS.md — session windows + StateStore
• docs/PHASE_39_5B_JOINS.md — keyed time-windowed stream-stream join
• docs/PHASE_DELTA_CDC_PLAN.md — CDC source mode

→ Full step-by-step walkthrough: docs/USER_GUIDE.md. → Runnable examples: examples/ (one per strategy + streaming + windowed + session + join + CDC). → Cutting a release: docs/RELEASE.md.

---

Development

# Build the Rust workspace (core + CLI + Python extension crate)
cargo build --release

# Build + install the Python extension into a venv
python -m venv .venv && source .venv/bin/activate
pip install maturin
maturin develop --release

# The flow consume binary is built into target/release/flow
target/release/flow --help

# Run tests
cargo test --workspace --lib              # default (no Docker)
cargo test --workspace -- --ignored       # Docker integration tests
                                          # (Kafka, RabbitMQ, Pub/Sub
                                          # emulator, Kinesis via
                                          # LocalStack, MinIO,
                                          # Schema Registry, etc.)

pytest                                    # default Python suite
pytest -m integration                     # full integration (Docker)
pytest -m spark                           # opt-in Spark E2E

---

License

Apache-2.0